Fixed #16187 -- refactored ORM lookup system

Allowed users to specify which lookups or transforms ("nested lookus")
are available for fields. The implementation is now class based.

Squashed commit of the following:

commit fa7a7195f1952a9c8dea7f6e89ee13f81757eda7
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Jan 18 10:53:24 2014 +0200

    Added lookup registration API docs

commit eb1c8ce164325e0d8641f14202e12486c70efdb6
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Tue Jan 14 18:59:36 2014 +0200

    Release notes and other minor docs changes

commit 11501c29c9352d17f22f3a0f59d3b805913dedcc
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sun Jan 12 20:53:03 2014 +0200

    Forgot to add custom_lookups tests in prev commit

commit 83173b960ea7eb2b24d573f326be59948df33536
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sun Jan 12 19:59:12 2014 +0200

    Renamed Extract -> Transform

commit 3b18d9f3a1bcdd93280f79654eba0efa209377bd
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sun Jan 12 19:51:53 2014 +0200

    Removed suggestion of temporary lookup registration from docs

commit 21d0c7631c161fc0c67911480be5d3f13f1afa68
Merge: 2509006 f2dc442
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sun Jan 12 09:38:23 2014 -0800

    Merge pull request #2 from mjtamlyn/lookups_3

    Reworked custom lookups docs.

commit f2dc4429a1da04c858364972eea57a35a868dab4
Author: Marc Tamlyn <marc.tamlyn@gmail.com>
Date:   Sun Jan 12 13:15:05 2014 +0000

    Reworked custom lookups docs.

    Mostly just formatting and rewording, but also replaced the example
    using ``YearExtract`` to  use an example which is unlikely to ever be
    possible directly in the ORM.

commit 250900650628d1f11beadb22814abd666029fb81
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sun Jan 12 13:19:13 2014 +0200

    Removed unused import

commit 4fba5dfaa022653ffa72497258ffd8f8b7476f92
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Jan 11 22:34:41 2014 +0200

    Added docs to index

commit 6d53963f375c77a1f287833b19b976d23f36c30b
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Jan 11 22:10:24 2014 +0200

    Dead code removal

commit f9cc0390078e21f1ea5a7bc1f15b09f8f6b0904d
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Jan 11 19:00:43 2014 +0200

    A new try for docs

commit 33aa18a6e3c831930bda0028222a26f9c1d96e66
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Jan 11 14:57:12 2014 +0200

    Renamed get_cols to get_group_by_cols

commit c7d5f8661b7d364962bed2e6f81161c1b4f1bcc3
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Jan 11 14:45:53 2014 +0200

    Altered query string customization for backends vendors

    The new way is trying to call first method 'as_' + connection.vendor.
    If that doesn't exist, then call as_sql().

    Also altered how lookup registration is done. There is now
    RegisterLookupMixin class that is used by Field, Extract and
    sql.Aggregate. This allows one to register lookups for extracts and
    aggregates in the same way lookup registration is done for fields.

commit 90e7004ec14e15503f828cc9bde2a7dab593814d
Merge: 66649ff f7c2c0a
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Jan 11 13:21:01 2014 +0200

    Merge branch 'master' into lookups_3

commit 66649ff891c7c73c7eecf6038c9a6802611b5d8a
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Jan 11 13:16:01 2014 +0200

    Some rewording in docs

commit 31b8faa62714b4b6b6057a9f5cc106c4dd73caab
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sun Dec 29 15:52:29 2013 +0200

    Cleanup based on review comments

commit 1016159f34674c0df871ed891cde72be8340bb5d
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Dec 28 18:37:04 2013 +0200

    Proof-of-concept fix for #16731

    Implemented only for SQLite and PostgreSQL, and only for startswith
    and istartswith lookups.

commit 193cd097ca8f2cc6a911e57b8e3fb726f96ee6a6
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Dec 28 17:57:58 2013 +0200

    Fixed #11722 -- iexact=F() produced invalid SQL

commit 08ed3c3b49e100ed9019831e770c25c8f61b70f9
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Dec 21 23:59:52 2013 +0200

    Made Lookup and Extract available from django.db.models

commit b99c8d83c972786c6fcd0e84c9e5cb08c1368300
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Dec 21 23:06:29 2013 +0200

    Fixed review notes by Loic

commit 049eebc0703c151127f4f0265beceea7b8b39e72
Merge: ed8fab7 b80a835
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Dec 21 22:53:10 2013 +0200

    Merge branch 'master' into lookups_3

    Conflicts:
    	django/db/models/fields/__init__.py
    	django/db/models/sql/compiler.py
    	django/db/models/sql/query.py
    	tests/null_queries/tests.py

commit ed8fab7fe8867ff3eb801c3697a426478387bb2f
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Dec 21 22:47:23 2013 +0200

    Made Extracts aware of full lookup path

commit 27a57b7aed91b2f346abc4a77da838bffa17c727
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sun Dec 1 21:10:11 2013 +0200

    Removed debugger import

commit 074e0f5aca0572e368c11e6d2c73c9026e7d63d7
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sun Dec 1 21:02:16 2013 +0200

    GIS lookup support added

commit 760e28e72bae475b442b026650969b0d182dbe53
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sun Dec 1 20:04:31 2013 +0200

    Removed usage of Constraint, used Lookup instead

commit eac47766844b90e7d3269e7a8c012eee34ec0093
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sun Dec 1 02:22:30 2013 +0200

    Minor cleanup of Lookup API

commit 2adf50428d59a783078b0da3d5d035106640c899
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sun Dec 1 02:14:19 2013 +0200

    Added documentation, polished implementation

commit 32c04357a87e3727a34f8c5e6ec0114d1fbbb303
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Nov 30 23:10:15 2013 +0200

    Avoid OrderedDict creation on lookup aggregate check

commit 7c8b3a32cc17b4dbca160921d48125f1631e0df4
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Sat Nov 30 23:04:34 2013 +0200

    Implemented nested lookups

    But there is no support of using lookups outside filtering yet.

commit 4d219d4cdef21d9c14e5d6b9299d583d1975fcba
Author: Anssi Kääriäinen <akaariai@gmail.com>
Date:   Wed Nov 27 22:07:30 2013 +0200

    Initial implementation of custom lookups

django/contrib/contenttypes/generic.py

@@ -12,7 +12,7 @@ from django.db import models, router, transaction, DEFAULT_DB_ALIAS
 from django.db.models import signals
 from django.db.models.fields.related import ForeignObject, ForeignObjectRel
 from django.db.models.related import PathInfo
-from django.db.models.sql.where import Constraint
+from django.db.models.sql.datastructures import Col
 from django.forms import ModelForm, ALL_FIELDS
 from django.forms.models import (BaseModelFormSet, modelformset_factory,
     modelform_defines_fields)
@@ -236,7 +236,8 @@ class GenericRelation(ForeignObject):
         field = self.rel.to._meta.get_field_by_name(self.content_type_field_name)[0]
         contenttype_pk = self.get_content_type().pk
         cond = where_class()
-        cond.add((Constraint(remote_alias, field.column, field), 'exact', contenttype_pk), 'AND')
+        lookup = field.get_lookup('exact')(Col(remote_alias, field, field), contenttype_pk)
+        cond.add(lookup, 'AND')
         return cond
 
     def bulk_related_objects(self, objs, using=DEFAULT_DB_ALIAS):

django/contrib/gis/db/backends/mysql/operations.py

@@ -49,9 +49,7 @@ class MySQLOperations(DatabaseOperations, BaseSpatialOperations):
         return placeholder
 
     def spatial_lookup_sql(self, lvalue, lookup_type, value, field, qn):
-        alias, col, db_type = lvalue
-
-        geo_col = '%s.%s' % (qn(alias), qn(col))
+        geo_col, db_type = lvalue
 
         lookup_info = self.geometry_functions.get(lookup_type, False)
         if lookup_info:

django/contrib/gis/db/backends/oracle/operations.py

@@ -231,10 +231,7 @@ class OracleOperations(DatabaseOperations, BaseSpatialOperations):
 
     def spatial_lookup_sql(self, lvalue, lookup_type, value, field, qn):
         "Returns the SQL WHERE clause for use in Oracle spatial SQL construction."
-        alias, col, db_type = lvalue
-
-        # Getting the quoted table name as `geo_col`.
-        geo_col = '%s.%s' % (qn(alias), qn(col))
+        geo_col, db_type = lvalue
 
         # See if a Oracle Geometry function matches the lookup type next
         lookup_info = self.geometry_functions.get(lookup_type, False)

django/contrib/gis/db/backends/postgis/operations.py

@@ -478,10 +478,7 @@ class PostGISOperations(DatabaseOperations, BaseSpatialOperations):
         (alias, col, db_type), the lookup type string, lookup value, and
         the geometry field.
         """
-        alias, col, db_type = lvalue
-
-        # Getting the quoted geometry column.
-        geo_col = '%s.%s' % (qn(alias), qn(col))
+        geo_col, db_type = lvalue
 
         if lookup_type in self.geometry_operators:
             if field.geography and not lookup_type in self.geography_operators:

django/contrib/gis/db/backends/spatialite/operations.py

@@ -324,10 +324,7 @@ class SpatiaLiteOperations(DatabaseOperations, BaseSpatialOperations):
         [a tuple of (alias, column, db_type)], lookup type, lookup
         value, the model field, and the quoting function.
         """
-        alias, col, db_type = lvalue
-
-        # Getting the quoted field as `geo_col`.
-        geo_col = '%s.%s' % (qn(alias), qn(col))
+        geo_col, db_type = lvalue
 
         if lookup_type in self.geometry_functions:
             # See if a SpatiaLite geometry function matches the lookup type.

django/contrib/gis/db/models/constants.py

@@ -0,0 +1,15 @@
+from django.db.models.sql.constants import QUERY_TERMS
+
+GIS_LOOKUPS = {
+    'bbcontains', 'bboverlaps', 'contained', 'contains',
+    'contains_properly', 'coveredby', 'covers', 'crosses', 'disjoint',
+    'distance_gt', 'distance_gte', 'distance_lt', 'distance_lte',
+    'dwithin', 'equals', 'exact',
+    'intersects', 'overlaps', 'relate', 'same_as', 'touches', 'within',
+    'left', 'right', 'overlaps_left', 'overlaps_right',
+    'overlaps_above', 'overlaps_below',
+    'strictly_above', 'strictly_below'
+}
+ALL_TERMS = GIS_LOOKUPS | QUERY_TERMS
+
+__all__ = ['ALL_TERMS', 'GIS_LOOKUPS']

django/contrib/gis/db/models/fields.py

@@ -2,6 +2,8 @@ from django.db.models.fields import Field
 from django.db.models.sql.expressions import SQLEvaluator
 from django.utils.translation import ugettext_lazy as _
 from django.contrib.gis import forms
+from django.contrib.gis.db.models.constants import GIS_LOOKUPS
+from django.contrib.gis.db.models.lookups import GISLookup
 from django.contrib.gis.db.models.proxy import GeometryProxy
 from django.contrib.gis.geometry.backend import Geometry, GeometryException
 from django.utils import six
@@ -284,6 +286,10 @@ class GeometryField(Field):
         """
         return connection.ops.get_geom_placeholder(self, value)
 
+for lookup_name in GIS_LOOKUPS:
+    lookup = type(lookup_name, (GISLookup,), {'lookup_name': lookup_name})
+    GeometryField.register_lookup(lookup)
+
 
 # The OpenGIS Geometry Type Fields
 class PointField(GeometryField):

django/contrib/gis/db/models/lookups.py

@@ -0,0 +1,28 @@
+from django.db.models.lookups import Lookup
+from django.db.models.sql.expressions import SQLEvaluator
+
+
+class GISLookup(Lookup):
+    def as_sql(self, qn, connection):
+        from django.contrib.gis.db.models.sql import GeoWhereNode
+        # We use the same approach as was used by GeoWhereNode. It would
+        # be a good idea to upgrade GIS to use similar code that is used
+        # for other lookups.
+        if isinstance(self.rhs, SQLEvaluator):
+            # Make sure the F Expression destination field exists, and
+            # set an `srid` attribute with the same as that of the
+            # destination.
+            geo_fld = GeoWhereNode._check_geo_field(self.rhs.opts, self.rhs.expression.name)
+            if not geo_fld:
+                raise ValueError('No geographic field found in expression.')
+            self.rhs.srid = geo_fld.srid
+        db_type = self.lhs.output_type.db_type(connection=connection)
+        params = self.lhs.output_type.get_db_prep_lookup(
+            self.lookup_name, self.rhs, connection=connection)
+        lhs_sql, lhs_params = self.process_lhs(qn, connection)
+        # lhs_params not currently supported.
+        assert not lhs_params
+        data = (lhs_sql, db_type)
+        spatial_sql, spatial_params = connection.ops.spatial_lookup_sql(
+            data, self.lookup_name, self.rhs, self.lhs.output_type, qn)
+        return spatial_sql, spatial_params + params

django/contrib/gis/db/models/sql/query.py

@@ -1,6 +1,7 @@
 from django.db import connections
 from django.db.models.query import sql
 
+from django.contrib.gis.db.models.constants import ALL_TERMS
 from django.contrib.gis.db.models.fields import GeometryField
 from django.contrib.gis.db.models.sql import aggregates as gis_aggregates
 from django.contrib.gis.db.models.sql.conversion import AreaField, DistanceField, GeomField
@@ -9,19 +10,6 @@ from django.contrib.gis.geometry.backend import Geometry
 from django.contrib.gis.measure import Area, Distance
 
 
-ALL_TERMS = set([
-    'bbcontains', 'bboverlaps', 'contained', 'contains',
-    'contains_properly', 'coveredby', 'covers', 'crosses', 'disjoint',
-    'distance_gt', 'distance_gte', 'distance_lt', 'distance_lte',
-    'dwithin', 'equals', 'exact',
-    'intersects', 'overlaps', 'relate', 'same_as', 'touches', 'within',
-    'left', 'right', 'overlaps_left', 'overlaps_right',
-    'overlaps_above', 'overlaps_below',
-    'strictly_above', 'strictly_below'
-])
-ALL_TERMS.update(sql.constants.QUERY_TERMS)
-
-
 class GeoQuery(sql.Query):
     """
     A single spatial SQL query.

django/db/backends/__init__.py

@@ -673,6 +673,9 @@ class BaseDatabaseFeatures(object):
     # What kind of error does the backend throw when accessing closed cursor?
     closed_cursor_error_class = ProgrammingError
 
+    # Does 'a' LIKE 'A' match?
+    has_case_insensitive_like = True
+
     def __init__(self, connection):
         self.connection = connection
 

django/db/backends/postgresql_psycopg2/base.py

@@ -62,6 +62,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_combined_alters = True
     nulls_order_largest = True
     closed_cursor_error_class = InterfaceError
+    has_case_insensitive_like = False
 
 
 class DatabaseWrapper(BaseDatabaseWrapper):
@@ -83,6 +84,11 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         'iendswith': 'LIKE UPPER(%s)',
     }
 
+    pattern_ops = {
+        'startswith': "LIKE %s || '%%%%'",
+        'istartswith': "LIKE UPPER(%s) || '%%%%'",
+    }
+
     Database = Database
 
     def __init__(self, *args, **kwargs):

django/db/backends/sqlite3/base.py

@@ -334,6 +334,11 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         'iendswith': "LIKE %s ESCAPE '\\'",
     }
 
+    pattern_ops = {
+        'startswith': "LIKE %s || '%%%%'",
+        'istartswith': "LIKE UPPER(%s) || '%%%%'",
+    }
+
     Database = Database
 
     def __init__(self, *args, **kwargs):

django/db/models/__init__.py

@@ -17,6 +17,7 @@ from django.db.models.fields.related import (  # NOQA
 from django.db.models.fields.proxy import OrderWrt  # NOQA
 from django.db.models.deletion import (  # NOQA
     CASCADE, PROTECT, SET, SET_NULL, SET_DEFAULT, DO_NOTHING, ProtectedError)
+from django.db.models.lookups import Lookup, Transform  # NOQA
 from django.db.models import signals  # NOQA
 
 

django/db/models/aggregates.py

@@ -15,10 +15,11 @@ def refs_aggregate(lookup_parts, aggregates):
     default annotation names we must check each prefix of the lookup_parts
     for match.
     """
-    for i in range(len(lookup_parts) + 1):
-        if LOOKUP_SEP.join(lookup_parts[0:i]) in aggregates:
-            return True
-    return False
+    for n in range(len(lookup_parts) + 1):
+        level_n_lookup = LOOKUP_SEP.join(lookup_parts[0:n])
+        if level_n_lookup in aggregates:
+            return aggregates[level_n_lookup], lookup_parts[n:]
+    return False, ()
 
 
 class Aggregate(object):

django/db/models/fields/__init__.py

@@ -11,6 +11,7 @@ from itertools import tee
 
 from django.apps import apps
 from django.db import connection
+from django.db.models.lookups import default_lookups, RegisterLookupMixin
 from django.db.models.query_utils import QueryWrapper
 from django.conf import settings
 from django import forms
@@ -80,7 +81,7 @@ def _empty(of_cls):
 
 
 @total_ordering
-class Field(object):
+class Field(RegisterLookupMixin):
     """Base class for all field types"""
 
     # Designates whether empty strings fundamentally are allowed at the
@@ -101,6 +102,7 @@ class Field(object):
         'unique': _('%(model_name)s with this %(field_label)s '
                     'already exists.'),
     }
+    class_lookups = default_lookups.copy()
 
     # Generic field type description, usually overridden by subclasses
     def _description(self):
@@ -514,8 +516,7 @@ class Field(object):
             except ValueError:
                 raise ValueError("The __year lookup type requires an integer "
                                  "argument")
-
-        raise TypeError("Field has invalid lookup: %s" % lookup_type)
+        return self.get_prep_value(value)
 
     def get_db_prep_lookup(self, lookup_type, value, connection,
                            prepared=False):
@@ -564,6 +565,8 @@ class Field(object):
                 return connection.ops.year_lookup_bounds_for_date_field(value)
             else:
                 return [value]          # this isn't supposed to happen
+        else:
+            return [value]
 
     def has_default(self):
         """

django/db/models/fields/related.py

@@ -5,9 +5,11 @@ from django.db.backends import utils
 from django.db.models import signals, Q
 from django.db.models.fields import (AutoField, Field, IntegerField,
     PositiveIntegerField, PositiveSmallIntegerField, FieldDoesNotExist)
+from django.db.models.lookups import IsNull
 from django.db.models.related import RelatedObject, PathInfo
 from django.db.models.query import QuerySet
 from django.db.models.deletion import CASCADE
+from django.db.models.sql.datastructures import Col
 from django.utils.encoding import smart_text
 from django.utils import six
 from django.utils.deprecation import RenameMethodsBase
@@ -987,6 +989,11 @@ class ForeignObjectRel(object):
         # example custom multicolumn joins currently have no remote field).
         self.field_name = None
 
+    def get_lookup_constraint(self, constraint_class, alias, targets, sources, lookup_type,
+                              raw_value):
+        return self.field.get_lookup_constraint(constraint_class, alias, targets, sources,
+                                                lookup_type, raw_value)
+
 
 class ManyToOneRel(ForeignObjectRel):
     def __init__(self, field, to, field_name, related_name=None, limit_choices_to=None,
@@ -1193,14 +1200,16 @@ class ForeignObject(RelatedField):
         pathinfos = [PathInfo(from_opts, opts, (opts.pk,), self.rel, not self.unique, False)]
         return pathinfos
 
-    def get_lookup_constraint(self, constraint_class, alias, targets, sources, lookup_type,
+    def get_lookup_constraint(self, constraint_class, alias, targets, sources, lookups,
                               raw_value):
-        from django.db.models.sql.where import SubqueryConstraint, Constraint, AND, OR
+        from django.db.models.sql.where import SubqueryConstraint, AND, OR
         root_constraint = constraint_class()
         assert len(targets) == len(sources)
+        if len(lookups) > 1:
+            raise exceptions.FieldError('Relation fields do not support nested lookups')
+        lookup_type = lookups[0]
 
         def get_normalized_value(value):
-
             from django.db.models import Model
             if isinstance(value, Model):
                 value_list = []
@@ -1221,28 +1230,27 @@ class ForeignObject(RelatedField):
                                                    [source.name for source in sources], raw_value),
                                 AND)
         elif lookup_type == 'isnull':
-            root_constraint.add(
-                (Constraint(alias, targets[0].column, targets[0]), lookup_type, raw_value), AND)
+            root_constraint.add(IsNull(Col(alias, targets[0], sources[0]), raw_value), AND)
         elif (lookup_type == 'exact' or (lookup_type in ['gt', 'lt', 'gte', 'lte']
                                          and not is_multicolumn)):
             value = get_normalized_value(raw_value)
-            for index, source in enumerate(sources):
+            for target, source, val in zip(targets, sources, value):
+                lookup_class = target.get_lookup(lookup_type)
                 root_constraint.add(
-                    (Constraint(alias, targets[index].column, sources[index]), lookup_type,
-                     value[index]), AND)
+                    lookup_class(Col(alias, target, source), val), AND)
         elif lookup_type in ['range', 'in'] and not is_multicolumn:
             values = [get_normalized_value(value) for value in raw_value]
             value = [val[0] for val in values]
-            root_constraint.add(
-                (Constraint(alias, targets[0].column, sources[0]), lookup_type, value), AND)
+            lookup_class = targets[0].get_lookup(lookup_type)
+            root_constraint.add(lookup_class(Col(alias, targets[0], sources[0]), value), AND)
         elif lookup_type == 'in':
             values = [get_normalized_value(value) for value in raw_value]
             for value in values:
                 value_constraint = constraint_class()
-                for index, target in enumerate(targets):
-                    value_constraint.add(
-                        (Constraint(alias, target.column, sources[index]), 'exact', value[index]),
-                        AND)
+                for source, target, val in zip(sources, targets, value):
+                    lookup_class = target.get_lookup('exact')
+                    lookup = lookup_class(Col(alias, target, source), val)
+                    value_constraint.add(lookup, AND)
                 root_constraint.add(value_constraint, OR)
         else:
             raise TypeError('Related Field got invalid lookup: %s' % lookup_type)

django/db/models/lookups.py

@@ -0,0 +1,317 @@
+from copy import copy
+import inspect
+
+from django.conf import settings
+from django.utils import timezone
+from django.utils.functional import cached_property
+
+
+class RegisterLookupMixin(object):
+    def get_lookup(self, lookup_name):
+        try:
+            return self.class_lookups[lookup_name]
+        except KeyError:
+            # To allow for inheritance, check parent class class lookups.
+            for parent in inspect.getmro(self.__class__):
+                if not 'class_lookups' in parent.__dict__:
+                    continue
+                if lookup_name in parent.class_lookups:
+                    return parent.class_lookups[lookup_name]
+        except AttributeError:
+            # This class didn't have any class_lookups
+            pass
+        if hasattr(self, 'output_type'):
+            return self.output_type.get_lookup(lookup_name)
+        return None
+
+    @classmethod
+    def register_lookup(cls, lookup):
+        if not 'class_lookups' in cls.__dict__:
+            cls.class_lookups = {}
+        cls.class_lookups[lookup.lookup_name] = lookup
+
+    @classmethod
+    def _unregister_lookup(cls, lookup):
+        """
+        Removes given lookup from cls lookups. Meant to be used in
+        tests only.
+        """
+        del cls.class_lookups[lookup.lookup_name]
+
+
+class Transform(RegisterLookupMixin):
+    def __init__(self, lhs, lookups):
+        self.lhs = lhs
+        self.init_lookups = lookups[:]
+
+    def as_sql(self, qn, connection):
+        raise NotImplementedError
+
+    @cached_property
+    def output_type(self):
+        return self.lhs.output_type
+
+    def relabeled_clone(self, relabels):
+        return self.__class__(self.lhs.relabeled_clone(relabels))
+
+    def get_group_by_cols(self):
+        return self.lhs.get_group_by_cols()
+
+
+class Lookup(RegisterLookupMixin):
+    lookup_name = None
+
+    def __init__(self, lhs, rhs):
+        self.lhs, self.rhs = lhs, rhs
+        self.rhs = self.get_prep_lookup()
+
+    def get_prep_lookup(self):
+        return self.lhs.output_type.get_prep_lookup(self.lookup_name, self.rhs)
+
+    def get_db_prep_lookup(self, value, connection):
+        return (
+            '%s', self.lhs.output_type.get_db_prep_lookup(
+                self.lookup_name, value, connection, prepared=True))
+
+    def process_lhs(self, qn, connection, lhs=None):
+        lhs = lhs or self.lhs
+        return qn.compile(lhs)
+
+    def process_rhs(self, qn, connection, rhs=None):
+        value = rhs or self.rhs
+        # Due to historical reasons there are a couple of different
+        # ways to produce sql here. get_compiler is likely a Query
+        # instance, _as_sql QuerySet and as_sql just something with
+        # as_sql. Finally the value can of course be just plain
+        # Python value.
+        if hasattr(value, 'get_compiler'):
+            value = value.get_compiler(connection=connection)
+        if hasattr(value, 'as_sql'):
+            sql, params = qn.compile(value)
+            return '(' + sql + ')', params
+        if hasattr(value, '_as_sql'):
+            sql, params = value._as_sql(connection=connection)
+            return '(' + sql + ')', params
+        else:
+            return self.get_db_prep_lookup(value, connection)
+
+    def relabeled_clone(self, relabels):
+        new = copy(self)
+        new.lhs = new.lhs.relabeled_clone(relabels)
+        if hasattr(new.rhs, 'relabeled_clone'):
+            new.rhs = new.rhs.relabeled_clone(relabels)
+        return new
+
+    def get_group_by_cols(self):
+        cols = self.lhs.get_group_by_cols()
+        if hasattr(self.rhs, 'get_group_by_cols'):
+            cols.extend(self.rhs.get_group_by_cols())
+        return cols
+
+    def as_sql(self, qn, connection):
+        raise NotImplementedError
+
+
+class BuiltinLookup(Lookup):
+    def as_sql(self, qn, connection):
+        lhs_sql, params = self.process_lhs(qn, connection)
+        field_internal_type = self.lhs.output_type.get_internal_type()
+        db_type = self.lhs.output_type
+        lhs_sql = connection.ops.field_cast_sql(db_type, field_internal_type) % lhs_sql
+        lhs_sql = connection.ops.lookup_cast(self.lookup_name) % lhs_sql
+        rhs_sql, rhs_params = self.process_rhs(qn, connection)
+        params.extend(rhs_params)
+        operator_plus_rhs = self.get_rhs_op(connection, rhs_sql)
+        return '%s %s' % (lhs_sql, operator_plus_rhs), params
+
+    def get_rhs_op(self, connection, rhs):
+        return connection.operators[self.lookup_name] % rhs
+
+
+default_lookups = {}
+
+
+class Exact(BuiltinLookup):
+    lookup_name = 'exact'
+default_lookups['exact'] = Exact
+
+
+class IExact(BuiltinLookup):
+    lookup_name = 'iexact'
+default_lookups['iexact'] = IExact
+
+
+class Contains(BuiltinLookup):
+    lookup_name = 'contains'
+default_lookups['contains'] = Contains
+
+
+class IContains(BuiltinLookup):
+    lookup_name = 'icontains'
+default_lookups['icontains'] = IContains
+
+
+class GreaterThan(BuiltinLookup):
+    lookup_name = 'gt'
+default_lookups['gt'] = GreaterThan
+
+
+class GreaterThanOrEqual(BuiltinLookup):
+    lookup_name = 'gte'
+default_lookups['gte'] = GreaterThanOrEqual
+
+
+class LessThan(BuiltinLookup):
+    lookup_name = 'lt'
+default_lookups['lt'] = LessThan
+
+
+class LessThanOrEqual(BuiltinLookup):
+    lookup_name = 'lte'
+default_lookups['lte'] = LessThanOrEqual
+
+
+class In(BuiltinLookup):
+    lookup_name = 'in'
+
+    def get_db_prep_lookup(self, value, connection):
+        params = self.lhs.output_type.get_db_prep_lookup(
+            self.lookup_name, value, connection, prepared=True)
+        if not params:
+            # TODO: check why this leads to circular import
+            from django.db.models.sql.datastructures import EmptyResultSet
+            raise EmptyResultSet
+        placeholder = '(' + ', '.join('%s' for p in params) + ')'
+        return (placeholder, params)
+
+    def get_rhs_op(self, connection, rhs):
+        return 'IN %s' % rhs
+default_lookups['in'] = In
+
+
+class PatternLookup(BuiltinLookup):
+    def get_rhs_op(self, connection, rhs):
+        # Assume we are in startswith. We need to produce SQL like:
+        #     col LIKE %s, ['thevalue%']
+        # For python values we can (and should) do that directly in Python,
+        # but if the value is for example reference to other column, then
+        # we need to add the % pattern match to the lookup by something like
+        #     col LIKE othercol || '%%'
+        # So, for Python values we don't need any special pattern, but for
+        # SQL reference values we need the correct pattern added.
+        value = self.rhs
+        if (hasattr(value, 'get_compiler') or hasattr(value, 'as_sql')
+                or hasattr(value, '_as_sql')):
+            return connection.pattern_ops[self.lookup_name] % rhs
+        else:
+            return super(PatternLookup, self).get_rhs_op(connection, rhs)
+
+
+class StartsWith(PatternLookup):
+    lookup_name = 'startswith'
+default_lookups['startswith'] = StartsWith
+
+
+class IStartsWith(PatternLookup):
+    lookup_name = 'istartswith'
+default_lookups['istartswith'] = IStartsWith
+
+
+class EndsWith(BuiltinLookup):
+    lookup_name = 'endswith'
+default_lookups['endswith'] = EndsWith
+
+
+class IEndsWith(BuiltinLookup):
+    lookup_name = 'iendswith'
+default_lookups['iendswith'] = IEndsWith
+
+
+class Between(BuiltinLookup):
+    def get_rhs_op(self, connection, rhs):
+        return "BETWEEN %s AND %s" % (rhs, rhs)
+
+
+class Year(Between):
+    lookup_name = 'year'
+default_lookups['year'] = Year
+
+
+class Range(Between):
+    lookup_name = 'range'
+default_lookups['range'] = Range
+
+
+class DateLookup(BuiltinLookup):
+
+    def process_lhs(self, qn, connection):
+        lhs, params = super(DateLookup, self).process_lhs(qn, connection)
+        tzname = timezone.get_current_timezone_name() if settings.USE_TZ else None
+        sql, tz_params = connection.ops.datetime_extract_sql(self.extract_type, lhs, tzname)
+        return connection.ops.lookup_cast(self.lookup_name) % sql, tz_params
+
+    def get_rhs_op(self, connection, rhs):
+        return '= %s' % rhs
+
+
+class Month(DateLookup):
+    lookup_name = 'month'
+    extract_type = 'month'
+default_lookups['month'] = Month
+
+
+class Day(DateLookup):
+    lookup_name = 'day'
+    extract_type = 'day'
+default_lookups['day'] = Day
+
+
+class WeekDay(DateLookup):
+    lookup_name = 'week_day'
+    extract_type = 'week_day'
+default_lookups['week_day'] = WeekDay
+
+
+class Hour(DateLookup):
+    lookup_name = 'hour'
+    extract_type = 'hour'
+default_lookups['hour'] = Hour
+
+
+class Minute(DateLookup):
+    lookup_name = 'minute'
+    extract_type = 'minute'
+default_lookups['minute'] = Minute
+
+
+class Second(DateLookup):
+    lookup_name = 'second'
+    extract_type = 'second'
+default_lookups['second'] = Second
+
+
+class IsNull(BuiltinLookup):
+    lookup_name = 'isnull'
+
+    def as_sql(self, qn, connection):
+        sql, params = qn.compile(self.lhs)
+        if self.rhs:
+            return "%s IS NULL" % sql, params
+        else:
+            return "%s IS NOT NULL" % sql, params
+default_lookups['isnull'] = IsNull
+
+
+class Search(BuiltinLookup):
+    lookup_name = 'search'
+default_lookups['search'] = Search
+
+
+class Regex(BuiltinLookup):
+    lookup_name = 'regex'
+default_lookups['regex'] = Regex
+
+
+class IRegex(BuiltinLookup):
+    lookup_name = 'iregex'
+default_lookups['iregex'] = IRegex

django/db/models/sql/aggregates.py

@@ -4,6 +4,7 @@ Classes to represent the default SQL aggregate functions
 import copy
 
 from django.db.models.fields import IntegerField, FloatField
+from django.db.models.lookups import RegisterLookupMixin
 
 
 __all__ = ['Aggregate', 'Avg', 'Count', 'Max', 'Min', 'StdDev', 'Sum', 'Variance']
@@ -14,7 +15,7 @@ ordinal_aggregate_field = IntegerField()
 computed_aggregate_field = FloatField()
 
 
-class Aggregate(object):
+class Aggregate(RegisterLookupMixin):
     """
     Default SQL Aggregate.
     """
@@ -93,6 +94,13 @@ class Aggregate(object):
 
         return self.sql_template % substitutions, params
 
+    def get_group_by_cols(self):
+        return []
+
+    @property
+    def output_type(self):
+        return self.field
+
 
 class Avg(Aggregate):
     is_computed = True

django/db/models/sql/compiler.py

@@ -45,7 +45,7 @@ class SQLCompiler(object):
         if self.query.select_related and not self.query.related_select_cols:
             self.fill_related_selections()
 
-    def quote_name_unless_alias(self, name):
+    def __call__(self, name):
         """
         A wrapper around connection.ops.quote_name that doesn't quote aliases
         for table names. This avoids problems with some SQL dialects that treat
@@ -61,6 +61,22 @@ class SQLCompiler(object):
         self.quote_cache[name] = r
         return r
 
+    def quote_name_unless_alias(self, name):
+        """
+        A wrapper around connection.ops.quote_name that doesn't quote aliases
+        for table names. This avoids problems with some SQL dialects that treat
+        quoted strings specially (e.g. PostgreSQL).
+        """
+        return self(name)
+
+    def compile(self, node):
+        vendor_impl = getattr(
+            node, 'as_' + self.connection.vendor, None)
+        if vendor_impl:
+            return vendor_impl(self, self.connection)
+        else:
+            return node.as_sql(self, self.connection)
+
     def as_sql(self, with_limits=True, with_col_aliases=False):
         """
         Creates the SQL for this query. Returns the SQL string and list of
@@ -88,11 +104,9 @@ class SQLCompiler(object):
         # docstring of get_from_clause() for details.
         from_, f_params = self.get_from_clause()
 
-        qn = self.quote_name_unless_alias
-
-        where, w_params = self.query.where.as_sql(qn=qn, connection=self.connection)
-        having, h_params = self.query.having.as_sql(qn=qn, connection=self.connection)
-        having_group_by = self.query.having.get_cols()
+        where, w_params = self.compile(self.query.where)
+        having, h_params = self.compile(self.query.having)
+        having_group_by = self.query.having.get_group_by_cols()
         params = []
         for val in six.itervalues(self.query.extra_select):
             params.extend(val[1])
@@ -180,7 +194,7 @@ class SQLCompiler(object):
         (without the table names) are given unique aliases. This is needed in
         some cases to avoid ambiguity with nested queries.
         """
-        qn = self.quote_name_unless_alias
+        qn = self
         qn2 = self.connection.ops.quote_name
         result = ['(%s) AS %s' % (col[0], qn2(alias)) for alias, col in six.iteritems(self.query.extra_select)]
         params = []
@@ -213,7 +227,7 @@ class SQLCompiler(object):
                         aliases.add(r)
                         col_aliases.add(col[1])
                 else:
-                    col_sql, col_params = col.as_sql(qn, self.connection)
+                    col_sql, col_params = self.compile(col)
                     result.append(col_sql)
                     params.extend(col_params)
 
@@ -229,7 +243,7 @@ class SQLCompiler(object):
 
         max_name_length = self.connection.ops.max_name_length()
         for alias, aggregate in self.query.aggregate_select.items():
-            agg_sql, agg_params = aggregate.as_sql(qn, self.connection)
+            agg_sql, agg_params = self.compile(aggregate)
             if alias is None:
                 result.append(agg_sql)
             else:
@@ -267,7 +281,7 @@ class SQLCompiler(object):
         result = []
         if opts is None:
             opts = self.query.get_meta()
-        qn = self.quote_name_unless_alias
+        qn = self
         qn2 = self.connection.ops.quote_name
         aliases = set()
         only_load = self.deferred_to_columns()
@@ -319,7 +333,7 @@ class SQLCompiler(object):
         Note that this method can alter the tables in the query, and thus it
         must be called before get_from_clause().
         """
-        qn = self.quote_name_unless_alias
+        qn = self
         qn2 = self.connection.ops.quote_name
         result = []
         opts = self.query.get_meta()
@@ -352,7 +366,7 @@ class SQLCompiler(object):
             ordering = (self.query.order_by
                         or self.query.get_meta().ordering
                         or [])
-        qn = self.quote_name_unless_alias
+        qn = self
         qn2 = self.connection.ops.quote_name
         distinct = self.query.distinct
         select_aliases = self._select_aliases
@@ -490,7 +504,7 @@ class SQLCompiler(object):
         ordering and distinct must be done first.
         """
         result = []
-        qn = self.quote_name_unless_alias
+        qn = self
         qn2 = self.connection.ops.quote_name
         first = True
         from_params = []
@@ -508,8 +522,7 @@ class SQLCompiler(object):
                 extra_cond = join_field.get_extra_restriction(
                     self.query.where_class, alias, lhs)
                 if extra_cond:
-                    extra_sql, extra_params = extra_cond.as_sql(
-                        qn, self.connection)
+                    extra_sql, extra_params = self.compile(extra_cond)
                     extra_sql = 'AND (%s)' % extra_sql
                     from_params.extend(extra_params)
                 else:
@@ -541,7 +554,7 @@ class SQLCompiler(object):
         """
         Returns a tuple representing the SQL elements in the "group by" clause.
         """
-        qn = self.quote_name_unless_alias
+        qn = self
         result, params = [], []
         if self.query.group_by is not None:
             select_cols = self.query.select + self.query.related_select_cols
@@ -560,7 +573,7 @@ class SQLCompiler(object):
                 if isinstance(col, (list, tuple)):
                     sql = '%s.%s' % (qn(col[0]), qn(col[1]))
                 elif hasattr(col, 'as_sql'):
-                    sql, col_params = col.as_sql(qn, self.connection)
+                    self.compile(col)
                 else:
                     sql = '(%s)' % str(col)
                 if sql not in seen:
@@ -784,7 +797,7 @@ class SQLCompiler(object):
         return result
 
     def as_subquery_condition(self, alias, columns, qn):
-        inner_qn = self.quote_name_unless_alias
+        inner_qn = self
         qn2 = self.connection.ops.quote_name
         if len(columns) == 1:
             sql, params = self.as_sql()
@@ -895,9 +908,9 @@ class SQLDeleteCompiler(SQLCompiler):
         """
         assert len(self.query.tables) == 1, \
             "Can only delete from one table at a time."
-        qn = self.quote_name_unless_alias
+        qn = self
         result = ['DELETE FROM %s' % qn(self.query.tables[0])]
-        where, params = self.query.where.as_sql(qn=qn, connection=self.connection)
+        where, params = self.compile(self.query.where)
         if where:
             result.append('WHERE %s' % where)
         return ' '.join(result), tuple(params)
@@ -913,7 +926,7 @@ class SQLUpdateCompiler(SQLCompiler):
         if not self.query.values:
             return '', ()
         table = self.query.tables[0]
-        qn = self.quote_name_unless_alias
+        qn = self
         result = ['UPDATE %s' % qn(table)]
         result.append('SET')
         values, update_params = [], []
@@ -933,7 +946,7 @@ class SQLUpdateCompiler(SQLCompiler):
                 val = SQLEvaluator(val, self.query, allow_joins=False)
             name = field.column
             if hasattr(val, 'as_sql'):
-                sql, params = val.as_sql(qn, self.connection)
+                sql, params = self.compile(val)
                 values.append('%s = %s' % (qn(name), sql))
                 update_params.extend(params)
             elif val is not None:
@@ -944,7 +957,7 @@ class SQLUpdateCompiler(SQLCompiler):
         if not values:
             return '', ()
         result.append(', '.join(values))
-        where, params = self.query.where.as_sql(qn=qn, connection=self.connection)
+        where, params = self.compile(self.query.where)
         if where:
             result.append('WHERE %s' % where)
         return ' '.join(result), tuple(update_params + params)
@@ -1024,11 +1037,11 @@ class SQLAggregateCompiler(SQLCompiler):
         parameters.
         """
         if qn is None:
-            qn = self.quote_name_unless_alias
+            qn = self
 
         sql, params = [], []
         for aggregate in self.query.aggregate_select.values():
-            agg_sql, agg_params = aggregate.as_sql(qn, self.connection)
+            agg_sql, agg_params = self.compile(aggregate)
             sql.append(agg_sql)
             params.extend(agg_params)
         sql = ', '.join(sql)

django/db/models/sql/datastructures.py

@@ -5,18 +5,27 @@ the SQL domain.
 
 
 class Col(object):
-    def __init__(self, alias, col):
-        self.alias = alias
-        self.col = col
+    def __init__(self, alias, target, source):
+        self.alias, self.target, self.source = alias, target, source
 
     def as_sql(self, qn, connection):
-        return '%s.%s' % (qn(self.alias), self.col), []
+        return "%s.%s" % (qn(self.alias), qn(self.target.column)), []
 
-    def prepare(self):
-        return self
+    @property
+    def output_type(self):
+        return self.source
 
     def relabeled_clone(self, relabels):
-        return self.__class__(relabels.get(self.alias, self.alias), self.col)
+        return self.__class__(relabels.get(self.alias, self.alias), self.target, self.source)
+
+    def get_group_by_cols(self):
+        return [(self.alias, self.target.column)]
+
+    def get_lookup(self, name):
+        return self.output_type.get_lookup(name)
+
+    def prepare(self):
+        return self
 
 
 class EmptyResultSet(Exception):

django/db/models/sql/expressions.py

@@ -24,11 +24,11 @@ class SQLEvaluator(object):
                                    (change_map.get(col[0], col[0]), col[1])))
         return clone
 
-    def get_cols(self):
+    def get_group_by_cols(self):
         cols = []
         for node, col in self.cols:
-            if hasattr(node, 'get_cols'):
-                cols.extend(node.get_cols())
+            if hasattr(node, 'get_group_by_cols'):
+                cols.extend(node.get_group_by_cols())
             elif isinstance(col, tuple):
                 cols.append(col)
         return cols

django/db/models/sql/query.py

@@ -19,6 +19,7 @@ from django.db.models.constants import LOOKUP_SEP
 from django.db.models.aggregates import refs_aggregate
 from django.db.models.expressions import ExpressionNode
 from django.db.models.fields import FieldDoesNotExist
+from django.db.models.lookups import Transform
 from django.db.models.query_utils import Q
 from django.db.models.related import PathInfo
 from django.db.models.sql import aggregates as base_aggregates_module
@@ -1028,13 +1029,16 @@ class Query(object):
         # Add the aggregate to the query
         aggregate.add_to_query(self, alias, col=col, source=source, is_summary=is_summary)
 
-    def prepare_lookup_value(self, value, lookup_type, can_reuse):
+    def prepare_lookup_value(self, value, lookups, can_reuse):
+        # Default lookup if none given is exact.
+        if len(lookups) == 0:
+            lookups = ['exact']
         # Interpret '__exact=None' as the sql 'is NULL'; otherwise, reject all
         # uses of None as a query value.
         if value is None:
-            if lookup_type not in ('exact', 'iexact'):
+            if lookups[-1] not in ('exact', 'iexact'):
                 raise ValueError("Cannot use None as a query value")
-            lookup_type = 'isnull'
+            lookups[-1] = 'isnull'
             value = True
         elif callable(value):
             warnings.warn(
@@ -1055,40 +1059,54 @@ class Query(object):
         # stage. Using DEFAULT_DB_ALIAS isn't nice, but it is the best we
         # can do here. Similar thing is done in is_nullable(), too.
         if (connections[DEFAULT_DB_ALIAS].features.interprets_empty_strings_as_nulls and
-                lookup_type == 'exact' and value == ''):
+                lookups[-1] == 'exact' and value == ''):
             value = True
-            lookup_type = 'isnull'
-        return value, lookup_type
+            lookups[-1] = ['isnull']
+        return value, lookups
 
     def solve_lookup_type(self, lookup):
         """
         Solve the lookup type from the lookup (eg: 'foobar__id__icontains')
         """
-        lookup_type = 'exact'  # Default lookup type
-        lookup_parts = lookup.split(LOOKUP_SEP)
-        num_parts = len(lookup_parts)
-        if (len(lookup_parts) > 1 and lookup_parts[-1] in self.query_terms
-                and (not self._aggregates or lookup not in self._aggregates)):
-            # Traverse the lookup query to distinguish related fields from
-            # lookup types.
-            lookup_model = self.model
-            for counter, field_name in enumerate(lookup_parts):
-                try:
-                    lookup_field = lookup_model._meta.get_field(field_name)
-                except FieldDoesNotExist:
-                    # Not a field. Bail out.
-                    lookup_type = lookup_parts.pop()
-                    break
-                # Unless we're at the end of the list of lookups, let's attempt
-                # to continue traversing relations.
-                if (counter + 1) < num_parts:
-                    try:
-                        lookup_model = lookup_field.rel.to
-                    except AttributeError:
-                        # Not a related field. Bail out.
-                        lookup_type = lookup_parts.pop()
-                        break
-        return lookup_type, lookup_parts
+        lookup_splitted = lookup.split(LOOKUP_SEP)
+        if self._aggregates:
+            aggregate, aggregate_lookups = refs_aggregate(lookup_splitted, self.aggregates)
+            if aggregate:
+                return aggregate_lookups, (), aggregate
+        _, field, _, lookup_parts = self.names_to_path(lookup_splitted, self.get_meta())
+        field_parts = lookup_splitted[0:len(lookup_splitted) - len(lookup_parts)]
+        if len(lookup_parts) == 0:
+            lookup_parts = ['exact']
+        elif len(lookup_parts) > 1:
+            if not field_parts:
+                raise FieldError(
+                    'Invalid lookup "%s" for model %s".' %
+                    (lookup, self.get_meta().model.__name__))
+        return lookup_parts, field_parts, False
+
+    def build_lookup(self, lookups, lhs, rhs):
+        lookups = lookups[:]
+        while lookups:
+            lookup = lookups[0]
+            next = lhs.get_lookup(lookup)
+            if next:
+                if len(lookups) == 1:
+                    # This was the last lookup, so return value lookup.
+                    if issubclass(next, Transform):
+                        lookups.append('exact')
+                        lhs = next(lhs, lookups)
+                    else:
+                        return next(lhs, rhs)
+                else:
+                    lhs = next(lhs, lookups)
+            # A field's get_lookup() can return None to opt for backwards
+            # compatibility path.
+            elif len(lookups) > 2:
+                raise FieldError(
+                    "Unsupported lookup for field '%s'" % lhs.output_type.name)
+            else:
+                return None
+            lookups = lookups[1:]
 
     def build_filter(self, filter_expr, branch_negated=False, current_negated=False,
                      can_reuse=None, connector=AND):
@@ -1118,21 +1136,24 @@ class Query(object):
         is responsible for unreffing the joins used.
         """
         arg, value = filter_expr
-        lookup_type, parts = self.solve_lookup_type(arg)
-        if not parts:
+        if not arg:
             raise FieldError("Cannot parse keyword query %r" % arg)
+        lookups, parts, reffed_aggregate = self.solve_lookup_type(arg)
 
         # Work out the lookup type and remove it from the end of 'parts',
         # if necessary.
-        value, lookup_type = self.prepare_lookup_value(value, lookup_type, can_reuse)
+        value, lookups = self.prepare_lookup_value(value, lookups, can_reuse)
         used_joins = getattr(value, '_used_joins', [])
 
         clause = self.where_class()
-        if self._aggregates:
-            for alias, aggregate in self.aggregates.items():
-                if alias in (parts[0], LOOKUP_SEP.join(parts)):
-                    clause.add((aggregate, lookup_type, value), AND)
-                    return clause, []
+        if reffed_aggregate:
+            condition = self.build_lookup(lookups, reffed_aggregate, value)
+            if not condition:
+                # Backwards compat for custom lookups
+                assert len(lookups) == 1
+                condition = (reffed_aggregate, lookups[0], value)
+            clause.add(condition, AND)
+            return clause, []
 
         opts = self.get_meta()
         alias = self.get_initial_alias()
@@ -1154,11 +1175,31 @@ class Query(object):
         targets, alias, join_list = self.trim_joins(sources, join_list, path)
 
         if hasattr(field, 'get_lookup_constraint'):
-            constraint = field.get_lookup_constraint(self.where_class, alias, targets, sources,
-                                                     lookup_type, value)
+            # For now foreign keys get special treatment. This should be
+            # refactored when composite fields lands.
+            condition = field.get_lookup_constraint(self.where_class, alias, targets, sources,
+                                                    lookups, value)
+            lookup_type = lookups[-1]
         else:
-            constraint = (Constraint(alias, targets[0].column, field), lookup_type, value)
-        clause.add(constraint, AND)
+            assert(len(targets) == 1)
+            col = Col(alias, targets[0], field)
+            condition = self.build_lookup(lookups, col, value)
+            if not condition:
+                # Backwards compat for custom lookups
+                if lookups[0] not in self.query_terms:
+                    raise FieldError(
+                        "Join on field '%s' not permitted. Did you "
+                        "misspell '%s' for the lookup type?" %
+                        (col.output_type.name, lookups[0]))
+                if len(lookups) > 1:
+                    raise FieldError("Nested lookup '%s' not supported." %
+                                     LOOKUP_SEP.join(lookups))
+                condition = (Constraint(alias, targets[0].column, field), lookups[0], value)
+                lookup_type = lookups[-1]
+            else:
+                lookup_type = condition.lookup_name
+
+        clause.add(condition, AND)
 
         require_outer = lookup_type == 'isnull' and value is True and not current_negated
         if current_negated and (lookup_type != 'isnull' or value is False):
@@ -1175,7 +1216,8 @@ class Query(object):
                 # (col IS NULL OR col != someval)
                 #   <=>
                 # NOT (col IS NOT NULL AND col = someval).
-                clause.add((Constraint(alias, targets[0].column, None), 'isnull', False), AND)
+                lookup_class = targets[0].get_lookup('isnull')
+                clause.add(lookup_class(Col(alias, targets[0], sources[0]), False), AND)
         return clause, used_joins if not require_outer else ()
 
     def add_filter(self, filter_clause):
@@ -1189,7 +1231,7 @@ class Query(object):
         if not self._aggregates:
             return False
         if not isinstance(obj, Node):
-            return (refs_aggregate(obj[0].split(LOOKUP_SEP), self.aggregates)
+            return (refs_aggregate(obj[0].split(LOOKUP_SEP), self.aggregates)[0]
                     or (hasattr(obj[1], 'contains_aggregate')
                         and obj[1].contains_aggregate(self.aggregates)))
         return any(self.need_having(c) for c in obj.children)
@@ -1277,7 +1319,7 @@ class Query(object):
         needed_inner = joinpromoter.update_join_types(self)
         return target_clause, needed_inner
 
-    def names_to_path(self, names, opts, allow_many):
+    def names_to_path(self, names, opts, allow_many=True, fail_on_missing=False):
         """
         Walks the names path and turns them PathInfo tuples. Note that a
         single name in 'names' can generate multiple PathInfos (m2m for
@@ -1297,9 +1339,10 @@ class Query(object):
             try:
                 field, model, direct, m2m = opts.get_field_by_name(name)
             except FieldDoesNotExist:
-                available = opts.get_all_field_names() + list(self.aggregate_select)
-                raise FieldError("Cannot resolve keyword %r into field. "
-                                 "Choices are: %s" % (name, ", ".join(available)))
+                # We didn't found the current field, so move position back
+                # one step.
+                pos -= 1
+                break
             # Check if we need any joins for concrete inheritance cases (the
             # field lives in parent, but we are currently in one of its
             # children)
@@ -1334,15 +1377,14 @@ class Query(object):
                 final_field = field
                 targets = (field,)
                 break
+        if pos == -1 or (fail_on_missing and pos + 1 != len(names)):
+            self.raise_field_error(opts, name)
+        return path, final_field, targets, names[pos + 1:]
 
-        if pos != len(names) - 1:
-            if pos == len(names) - 2:
-                raise FieldError(
-                    "Join on field %r not permitted. Did you misspell %r for "
-                    "the lookup type?" % (name, names[pos + 1]))
-            else:
-                raise FieldError("Join on field %r not permitted." % name)
-        return path, final_field, targets
+    def raise_field_error(self, opts, name):
+        available = opts.get_all_field_names() + list(self.aggregate_select)
+        raise FieldError("Cannot resolve keyword %r into field. "
+                         "Choices are: %s" % (name, ", ".join(available)))
 
     def setup_joins(self, names, opts, alias, can_reuse=None, allow_many=True):
         """
@@ -1371,8 +1413,9 @@ class Query(object):
         """
         joins = [alias]
         # First, generate the path for the names
-        path, final_field, targets = self.names_to_path(
-            names, opts, allow_many)
+        path, final_field, targets, rest = self.names_to_path(
+            names, opts, allow_many, fail_on_missing=True)
+
         # Then, add the path to the query's joins. Note that we can't trim
         # joins at this stage - we will need the information about join type
         # of the trimmed joins.
@@ -1387,8 +1430,6 @@ class Query(object):
             alias = self.join(
                 connection, reuse=reuse, nullable=nullable, join_field=join.join_field)
             joins.append(alias)
-        if hasattr(final_field, 'field'):
-            final_field = final_field.field
         return final_field, targets, opts, joins, path
 
     def trim_joins(self, targets, joins, path):
@@ -1451,17 +1492,19 @@ class Query(object):
         # nothing
         alias, col = query.select[0].col
         if self.is_nullable(query.select[0].field):
-            query.where.add((Constraint(alias, col, query.select[0].field), 'isnull', False), AND)
+            lookup_class = query.select[0].field.get_lookup('isnull')
+            lookup = lookup_class(Col(alias, query.select[0].field, query.select[0].field), False)
+            query.where.add(lookup, AND)
         if alias in can_reuse:
-            pk = query.select[0].field.model._meta.pk
+            select_field = query.select[0].field
+            pk = select_field.model._meta.pk
             # Need to add a restriction so that outer query's filters are in effect for
             # the subquery, too.
             query.bump_prefix(self)
-            query.where.add(
-                (Constraint(query.select[0].col[0], pk.column, pk),
-                 'exact', Col(alias, pk.column)),
-                AND
-            )
+            lookup_class = select_field.get_lookup('exact')
+            lookup = lookup_class(Col(query.select[0].col[0], pk, pk),
+                                  Col(alias, pk, pk))
+            query.where.add(lookup, AND)
 
         condition, needed_inner = self.build_filter(
             ('%s__in' % trimmed_prefix, query),

django/db/models/sql/subqueries.py

@@ -5,12 +5,12 @@ Query subclasses which provide extra functionality beyond simple data retrieval.
 from django.conf import settings
 from django.core.exceptions import FieldError
 from django.db import connections
+from django.db.models.query_utils import Q
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.fields import DateField, DateTimeField, FieldDoesNotExist
 from django.db.models.sql.constants import GET_ITERATOR_CHUNK_SIZE, SelectInfo
 from django.db.models.sql.datastructures import Date, DateTime
 from django.db.models.sql.query import Query
-from django.db.models.sql.where import AND, Constraint
 from django.utils import six
 from django.utils import timezone
 
@@ -42,10 +42,10 @@ class DeleteQuery(Query):
         if not field:
             field = self.get_meta().pk
         for offset in range(0, len(pk_list), GET_ITERATOR_CHUNK_SIZE):
-            where = self.where_class()
-            where.add((Constraint(None, field.column, field), 'in',
-                       pk_list[offset:offset + GET_ITERATOR_CHUNK_SIZE]), AND)
-            self.do_query(self.get_meta().db_table, where, using=using)
+            self.where = self.where_class()
+            self.add_q(Q(
+                **{field.attname + '__in': pk_list[offset:offset + GET_ITERATOR_CHUNK_SIZE]}))
+            self.do_query(self.get_meta().db_table, self.where, using=using)
 
     def delete_qs(self, query, using):
         """
@@ -80,9 +80,8 @@ class DeleteQuery(Query):
                     SelectInfo((self.get_initial_alias(), pk.column), None)
                 ]
                 values = innerq
-            where = self.where_class()
-            where.add((Constraint(None, pk.column, pk), 'in', values), AND)
-            self.where = where
+            self.where = self.where_class()
+            self.add_q(Q(pk__in=values))
         self.get_compiler(using).execute_sql(None)
 
 
@@ -113,13 +112,10 @@ class UpdateQuery(Query):
                 related_updates=self.related_updates.copy(), **kwargs)
 
     def update_batch(self, pk_list, values, using):
-        pk_field = self.get_meta().pk
         self.add_update_values(values)
         for offset in range(0, len(pk_list), GET_ITERATOR_CHUNK_SIZE):
             self.where = self.where_class()
-            self.where.add((Constraint(None, pk_field.column, pk_field), 'in',
-                            pk_list[offset:offset + GET_ITERATOR_CHUNK_SIZE]),
-                           AND)
+            self.add_q(Q(pk__in=pk_list[offset: offset + GET_ITERATOR_CHUNK_SIZE]))
             self.get_compiler(using).execute_sql(None)
 
     def add_update_values(self, values):

django/db/models/sql/where.py

@@ -5,6 +5,7 @@ Code to manage the creation and SQL rendering of 'where' constraints.
 import collections
 import datetime
 from itertools import repeat
+import warnings
 
 from django.conf import settings
 from django.db.models.fields import DateTimeField, Field
@@ -101,7 +102,7 @@ class WhereNode(tree.Node):
         for child in self.children:
             try:
                 if hasattr(child, 'as_sql'):
-                    sql, params = child.as_sql(qn=qn, connection=connection)
+                    sql, params = qn.compile(child)
                 else:
                     # A leaf node in the tree.
                     sql, params = self.make_atom(child, qn, connection)
@@ -152,16 +153,16 @@ class WhereNode(tree.Node):
                 sql_string = '(%s)' % sql_string
         return sql_string, result_params
 
-    def get_cols(self):
+    def get_group_by_cols(self):
         cols = []
         for child in self.children:
-            if hasattr(child, 'get_cols'):
-                cols.extend(child.get_cols())
+            if hasattr(child, 'get_group_by_cols'):
+                cols.extend(child.get_group_by_cols())
             else:
                 if isinstance(child[0], Constraint):
                     cols.append((child[0].alias, child[0].col))
-                if hasattr(child[3], 'get_cols'):
-                    cols.extend(child[3].get_cols())
+                if hasattr(child[3], 'get_group_by_cols'):
+                    cols.extend(child[3].get_group_by_cols())
         return cols
 
     def make_atom(self, child, qn, connection):
@@ -174,6 +175,9 @@ class WhereNode(tree.Node):
         Returns the string for the SQL fragment and the parameters to use for
         it.
         """
+        warnings.warn(
+            "The make_atom() method will be removed in Django 1.9. Use Lookup class instead.",
+            PendingDeprecationWarning)
         lvalue, lookup_type, value_annotation, params_or_value = child
         field_internal_type = lvalue.field.get_internal_type() if lvalue.field else None
 
@@ -193,13 +197,13 @@ class WhereNode(tree.Node):
             field_sql, field_params = self.sql_for_columns(lvalue, qn, connection, field_internal_type), []
         else:
             # A smart object with an as_sql() method.
-            field_sql, field_params = lvalue.as_sql(qn, connection)
+            field_sql, field_params = qn.compile(lvalue)
 
         is_datetime_field = value_annotation is datetime.datetime
         cast_sql = connection.ops.datetime_cast_sql() if is_datetime_field else '%s'
 
         if hasattr(params, 'as_sql'):
-            extra, params = params.as_sql(qn, connection)
+            extra, params = qn.compile(params)
             cast_sql = ''
         else:
             extra = ''
@@ -282,6 +286,8 @@ class WhereNode(tree.Node):
             if hasattr(child, 'relabel_aliases'):
                 # For example another WhereNode
                 child.relabel_aliases(change_map)
+            elif hasattr(child, 'relabeled_clone'):
+                self.children[pos] = child.relabeled_clone(change_map)
             elif isinstance(child, (list, tuple)):
                 # tuple starting with Constraint
                 child = (child[0].relabeled_clone(change_map),) + child[1:]
@@ -347,10 +353,13 @@ class Constraint(object):
     pre-process itself prior to including in the WhereNode.
     """
     def __init__(self, alias, col, field):
+        warnings.warn(
+            "The Constraint class will be removed in Django 1.9. Use Lookup class instead.",
+            PendingDeprecationWarning)
         self.alias, self.col, self.field = alias, col, field
 
     def prepare(self, lookup_type, value):
-        if self.field:
+        if self.field and not hasattr(value, 'as_sql'):
             return self.field.get_prep_lookup(lookup_type, value)
         return value
 

docs/howto/custom-model-fields.txt

@@ -662,6 +662,12 @@ Django filter lookups: ``exact``, ``iexact``, ``contains``, ``icontains``,
 ``endswith``, ``iendswith``, ``range``, ``year``, ``month``, ``day``,
 ``isnull``, ``search``, ``regex``, and ``iregex``.
 
+.. versionadded:: 1.7
+
+    If you are using :doc:`Custom lookups </ref/models/custom-lookups>` the
+    ``lookup_type`` can be any ``lookup_name`` used by the project's custom
+    lookups.
+
 Your method must be prepared to handle all of these ``lookup_type`` values and
 should raise either a ``ValueError`` if the ``value`` is of the wrong sort (a
 list when you were expecting an object, for example) or a ``TypeError`` if

docs/index.txt

@@ -81,7 +81,8 @@ manipulating the data of your Web application. Learn more about it below:
   :doc:`Transactions <topics/db/transactions>` |
   :doc:`Aggregation <topics/db/aggregation>` |
   :doc:`Custom fields <howto/custom-model-fields>` |
-  :doc:`Multiple databases <topics/db/multi-db>`
+  :doc:`Multiple databases <topics/db/multi-db>` |
+  :doc:`Custom lookups <ref/models/custom-lookups>`
 
 * **Other:**
   :doc:`Supported databases <ref/databases>` |

docs/ref/models/custom-lookups.txt

@@ -0,0 +1,336 @@
+==============
+Custom lookups
+==============
+
+.. versionadded:: 1.7
+
+.. module:: django.db.models.lookups
+   :synopsis: Custom lookups
+
+.. currentmodule:: django.db.models
+
+By default Django offers a wide variety of :ref:`built-in lookups
+<field-lookups>` for filtering (for example, ``exact`` and ``icontains``). This
+documentation explains how to write custom lookups and how to alter the working
+of existing lookups.
+
+A simple Lookup example
+~~~~~~~~~~~~~~~~~~~~~~~
+
+Let's start with a simple custom lookup. We will write a custom lookup ``ne``
+which works opposite to ``exact``. ``Author.objects.filter(name__ne='Jack')``
+will translate to the SQL::
+
+  "author"."name" <> 'Jack'
+
+This SQL is backend independent, so we don't need to worry about different
+databases.
+
+There are two steps to making this work. Firstly we need to implement the
+lookup, then we need to tell Django about it. The implementation is quite
+straightforward::
+
+  from django.db.models import Lookup
+
+  class NotEqual(Lookup):
+      lookup_name = 'ne'
+
+      def as_sql(self, qn, connection):
+          lhs, lhs_params = self.process_lhs(qn, connection)
+          rhs, rhs_params = self.process_rhs(qn, connection)
+          params = lhs_params + rhs_params
+          return '%s <> %s' % (lhs, rhs), params
+
+To register the ``NotEqual`` lookup we will just need to call
+``register_lookup`` on the field class we want the lookup to be available. In
+this case, the lookup makes sense on all ``Field`` subclasses, so we register
+it with ``Field`` directly::
+
+  from django.db.models.fields import Field
+  Field.register_lookup(NotEqual)
+
+We can now use ``foo__ne`` for any field ``foo``. You will need to ensure that
+this registration happens before you try to create any querysets using it. You
+could place the implementation in a ``models.py`` file, or register the lookup
+in the ``ready()`` method of an ``AppConfig``.
+
+Taking a closer look at the implementation, the first required attribute is
+``lookup_name``. This allows the ORM to understand how to interpret ``name__ne``
+and use ``NotEqual`` to generate the SQL. By convention, these names are always
+lowercase strings containing only letters, but the only hard requirement is
+that it must not contain the string ``__``.
+
+A ``Lookup`` works against two values, ``lhs`` and ``rhs``, standing for
+left-hand side and right-hand side. The left-hand side is usually a field
+reference, but it can be anything implementing the :ref:`query expression API
+<query-expression>`. The right-hand is the value given by the user. In the
+example ``Author.objects.filter(name__ne='Jack')``, the left-hand side is a
+reference to the ``name`` field of the ``Author`` model, and ``'Jack'`` is the
+right-hand side.
+
+We call ``process_lhs`` and ``process_rhs`` to convert them into the values we
+need for SQL. In the above example, ``process_lhs`` returns
+``('"author"."name"', [])`` and ``process_rhs`` returns ``('"%s"', ['Jack'])``.
+In this example there were no parameters for the left hand side, but this would
+depend on the object we have, so we still need to include them in the
+parameters we return.
+
+Finally we combine the parts into a SQL expression with ``<>``, and supply all
+the parameters for the query. We then return a tuple containing the generated
+SQL string and the parameters.
+
+A simple transformer example
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The custom lookup above is great, but in some cases you may want to be able to
+chain lookups together. For example, let's suppose we are building an
+application where we want to make use of the ``abs()`` operator.
+We have an ``Experiment`` model which records a start value, end value and the
+change (start - end). We would like to find all experiments where the change
+was equal to a certain amount (``Experiment.objects.filter(change__abs=27)``),
+or where it did not exceede a certain amount
+(``Experiment.objects.filter(change__abs__lt=27)``).
+
+.. note::
+    This example is somewhat contrived, but it demonstrates nicely the range of
+    functionality which is possible in a database backend independent manner,
+    and without duplicating functionality already in Django.
+
+We will start by writing a ``AbsoluteValue`` transformer. This will use the SQL
+function ``ABS()`` to transform the value before comparison::
+
+  from django.db.models import Transform
+
+  class AbsoluteValue(Transform):
+      lookup_name = 'abs'
+
+      def as_sql(self, qn, connection):
+          lhs, params = qn.compile(self.lhs)
+          return "ABS(%s)" % lhs, params
+
+Next, lets register it for ``IntegerField``::
+
+  from django.db.models import IntegerField
+  IntegerField.register_lookup(AbsoluteValue)
+
+We can now run the queris we had before.
+``Experiment.objects.filter(change__abs=27)`` will generate the following SQL::
+
+    SELECT ... WHERE ABS("experiments"."change") = 27
+
+By using ``Transform`` instead of ``Lookup`` it means we are able to chain
+further lookups afterwards. So
+``Experiment.objects.filter(change__abs__lt=27)`` will generate the following
+SQL::
+
+    SELECT ... WHERE ABS("experiments"."change") < 27
+
+Subclasses of ``Transform`` usually only operate on the left-hand side of the
+expression. Further lookups will work on the transformed value. Note that in
+this case where there is no other lookup specified, Django interprets
+``change__abs=27`` as ``change__abs__exact=27``.
+
+When looking for which lookups are allowable after the ``Transform`` has been
+applied, Django uses the ``output_type`` attribute. We didn't need to specify
+this here as it didn't change, but supposing we were applying ``AbsoluteValue``
+to some field which represents a more complex type (for example a point
+relative to an origin, or a complex number) then we may have wanted to specify
+``output_type = FloatField``, which will ensure that further lookups like
+``abs__lte`` behave as they would for a ``FloatField``.
+
+Writing an efficient abs__lt lookup
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When using the above written ``abs`` lookup, the SQL produced will not use
+indexes efficiently in some cases. In particular, when we use
+``change__abs__lt=27``, this is equivalent to ``change__gt=-27`` AND
+``change__lt=27``. (For the ``lte`` case we could use the SQL ``BETWEEN``).
+
+So we would like ``Experiment.objects.filter(change__abs__lt=27)`` to generate
+the following SQL::
+
+    SELECT .. WHERE "experiments"."change" < 27 AND "experiments"."change" > -27
+
+The implementation is::
+
+  from django.db.models import Lookup
+
+  class AbsoluteValueLessThan(Lookup):
+      lookup_name = 'lt'
+
+      def as_sql(self, qn, connection):
+          lhs, lhs_params = qn.compile(self.lhs.lhs)
+          rhs, rhs_params = self.process_rhs(qn, connection)
+          params = lhs_params + rhs_params + lhs_params + rhs_params
+          return '%s > %s AND %s < -%s % (lhs, rhs, lhs, rhs), params
+
+  AbsoluteValue.register_lookup(AbsoluteValueLessThan)
+
+There are a couple of notable things going on. First, ``AbsoluteValueLessThan``
+isn't calling ``process_lhs()``. Instead it skips the transformation of the
+``lhs`` done by ``AbsoluteValue`` and uses the original ``lhs``. That is, we
+want to get ``27`` not ``ABS(27)``. Referring directly to ``self.lhs.lhs`` is
+safe as ``AbsoluteValueLessThan`` can be accessed only from the
+``AbsoluteValue`` lookup, that is the ``lhs`` is always an instance of
+``AbsoluteValue``.
+
+Notice also that  as both sides are used multiple times in the query the params
+need to contain ``lhs_params`` and ``rhs_params`` multiple times.
+
+The final query does the inversion (``27`` to ``-27``) directly in the
+database. The reason for doing this is that if the self.rhs is something else
+than a plain integer value (for example an ``F()`` reference) we can't do the
+transformations in Python.
+
+.. note::
+    In fact, most lookups with ``__abs`` could be implemented as range queries
+    like this, and on most database backend it is likely to be more sensible to
+    do so as you can make use of the indexes. However with PostgreSQL you may
+    want to add an index on ``abs(change)`` which would allow these queries to
+    be very efficient.
+
+Writing alternative implemenatations for existing lookups
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Sometimes different database vendors require different SQL for the same
+operation. For this example we will rewrite a custom implementation for
+MySQL for the NotEqual operator. Instead of ``<>`` we will be using ``!=``
+operator. (Note that in reality almost all databases support both, including
+all the official databases supported by Django).
+
+We can change the behaviour on a specific backend by creating a subclass of
+``NotEqual`` with a ``as_mysql`` method::
+
+  class MySQLNotEqual(NotEqual):
+      def as_mysql(self, qn, connection):
+          lhs, lhs_params = self.process_lhs(qn, connection)
+          rhs, rhs_params = self.process_rhs(qn, connection)
+          params = lhs_params + rhs_params
+          return '%s != %s' % (lhs, rhs), params
+  Field.register_lookup(MySQLNotExact)
+
+We can then register it with ``Field``. It takes the place of the original
+``NotEqual`` class as it has 
+
+When compiling a query, Django first looks for ``as_%s % connection.vendor``
+methods, and then falls back to ``as_sql``. The vendor names for the in-built
+backends are ``sqlite``, ``postgresql``, ``oracle`` and ``mysql``.
+
+.. _query-expression:
+
+The Query Expression API
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+A lookup can assume that the lhs responds to the query expression API.
+Currently direct field references, aggregates and ``Transform`` instances respond
+to this API.
+
+.. method:: as_sql(qn, connection)
+
+    Responsible for producing the query string and parameters for the
+    expression. The ``qn`` has a ``compile()`` method that can be used to
+    compile other expressions. The ``connection`` is the connection used to
+    execute the query.
+
+    Calling expression.as_sql() directly is usually incorrect - instead
+    qn.compile(expression) should be used. The qn.compile() method will take
+    care of calling vendor-specific methods of the expression.
+
+.. method:: get_lookup(lookup_name)
+
+    The ``get_lookup()`` method is used to fetch lookups. By default the
+    lookup is fetched from the expression's output type in the same way
+    described in registering and fetching lookup documentation below.
+    It is possible to override this method to alter that behaviour.
+
+.. method:: as_vendorname(qn, connection)
+
+    Works like ``as_sql()`` method. When an expression is compiled by
+    ``qn.compile()``, Django will first try to call ``as_vendorname()``, where
+    vendorname is the vendor name of the backend used for executing the query.
+    The vendorname is one of ``postgresql``, ``oracle``, ``sqlite`` or
+    ``mysql`` for Django's built-in backends.
+
+.. attribute:: output_type
+
+    The ``output_type`` attribute is used by the ``get_lookup()`` method to check for
+    lookups. The output_type should be a field.
+
+Note that this documentation lists only the public methods of the API.
+
+Lookup reference
+~~~~~~~~~~~~~~~~
+
+.. class:: Lookup
+
+    In addition to the attributes and methods below, lookups also support
+    ``as_sql`` and ``as_vendorname`` from the query expression API.
+
+.. attribute:: lhs
+
+    The ``lhs`` (left-hand side) of a lookup tells us what we are comparing the
+    rhs to. It is an object which implements the query expression API. This is
+    likely to be a field, an aggregate or a subclass of ``Transform``.
+
+.. attribute:: rhs
+
+    The ``rhs`` (right-hand side) of a lookup is the value we are comparing the
+    left hand side to. It may be a plain value, or something which compiles
+    into SQL, for example an ``F()`` object or a ``Queryset``.
+
+.. attribute:: lookup_name
+
+    This class level attribute is used when registering lookups. It determines
+    the name used in queries to trigger this lookup. For example, ``contains``
+    or ``exact``. This should not contain the string ``__``.
+
+.. method:: process_lhs(qn, connection)
+
+    This returns a tuple of ``(lhs_string, lhs_params)``. In some cases you may
+    wish to compile ``lhs`` directly in your ``as_sql`` methods using
+    ``qn.compile(self.lhs)``.
+
+.. method:: process_rhs(qn, connection)
+
+    Behaves the same as ``process_lhs`` but acts on the right-hand side.
+
+Transform reference
+~~~~~~~~~~~~~~~~~~~
+
+.. class:: Transform
+
+    In addition to implementing the query expression API Transforms have the
+    following methods and attributes.
+
+.. attribute:: lhs
+
+    The ``lhs`` (left-hand-side) of a transform contains the value to be
+    transformed. The ``lhs`` implements the query expression API.
+
+.. attribute:: lookup_name
+
+    This class level attribute is used when registering lookups. It determines
+    the name used in queries to trigger this lookup. For example, ``year``
+    or ``dayofweek``. This should not contain the string ``__``.
+
+.. _lookup-registration-api:
+
+Registering and fetching lookups
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The lookup registration API is explained below.
+
+.. classmethod:: register_lookup(lookup)
+
+    Registers the Lookup or Transform for the class. For example
+    ``DateField.register_lookup(YearExact)`` will register ``YearExact`` for
+    all ``DateFields`` in the project, but also for fields that are instances
+    of a subclass of ``DateField`` (for example ``DateTimeField``).
+
+.. method:: get_lookup(lookup_name)
+
+    Django uses ``get_lookup(lookup_name)`` to fetch lookups or transforms.
+    The implementation of ``get_lookup()`` fetches lookups or transforms
+    registered for the current class based on their lookup_name attribute.
+
+The lookup registration API is available for ``Transform`` and ``Field`` classes.

docs/ref/models/fields.txt

@@ -343,6 +343,13 @@ underscores to spaces. See :ref:`Verbose field names <verbose-field-names>`.
 A list of validators to run for this field. See the :doc:`validators
 documentation </ref/validators>` for more information.
 
+Registering and fetching lookups
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``Field`` implements the :ref:`lookup registration API <lookup-registration-api>`.
+The API can be used to customize which lookups are available for a field class, and
+how lookups are fetched from a field.
+
 .. _model-field-types:
 
 Field types

docs/ref/models/index.txt

@@ -13,3 +13,4 @@ Model API reference. For introductory material, see :doc:`/topics/db/models`.
    instances
    querysets
    queries
+   custom-lookups

docs/ref/models/querysets.txt

@@ -1995,6 +1995,9 @@ specified as keyword arguments to the ``QuerySet`` methods :meth:`filter()`,
 For an introduction, see :ref:`models and database queries documentation
 <field-lookups-intro>`.
 
+Django's inbuilt lookups are listed below. It is also possible to write
+:doc:`custom lookups </ref/models/custom-lookups>` for model fields.
+
 .. fieldlookup:: exact
 
 exact

docs/releases/1.7.txt

@@ -180,6 +180,27 @@ for the following, instead of backend specific behavior.
     finally:
         c.close()
 
+Custom lookups
+~~~~~~~~~~~~~~
+
+It is now possible to write custom lookups and transforms for the ORM.
+Custom lookups work just like Django's inbuilt lookups (e.g. ``lte``,
+``icontains``) while transforms are a new concept.
+
+The :class:`django.db.models.Lookup` class provides a way to add lookup
+operators for model fields. As an example it is possible to add ``day_lte``
+opertor for ``DateFields``.
+
+The :class:`django.db.models.Transform` class allows transformations of
+database values prior to the final lookup. For example it is possible to
+write a ``year`` transform that extracts year from the field's value.
+Transforms allow for chaining. After the ``year`` transform has been added
+to ``DateField`` it is possible to filter on the transformed value, for
+example ``qs.filter(author__birthdate__year__lte=1981)``.
+
+For more information about both custom lookups and transforms refer to
+:doc:`custom lookups </ref/models/custom-lookups>` documentation.
+
 Minor features
 ~~~~~~~~~~~~~~
 

tests/aggregation/tests.py

@@ -443,7 +443,7 @@ class BaseAggregateTestCase(TestCase):
         vals = Author.objects.filter(pk=1).aggregate(Count("friends__id"))
         self.assertEqual(vals, {"friends__id__count": 2})
 
-        books = Book.objects.annotate(num_authors=Count("authors__name")).filter(num_authors__ge=2).order_by("pk")
+        books = Book.objects.annotate(num_authors=Count("authors__name")).filter(num_authors__exact=2).order_by("pk")
         self.assertQuerysetEqual(
             books, [
                 "The Definitive Guide to Django: Web Development Done Right",

tests/custom_lookups/models.py

@@ -0,0 +1,13 @@
+from django.db import models
+from django.utils.encoding import python_2_unicode_compatible
+
+
+@python_2_unicode_compatible
+class Author(models.Model):
+    name = models.CharField(max_length=20)
+    age = models.IntegerField(null=True)
+    birthdate = models.DateField(null=True)
+    average_rating = models.FloatField(null=True)
+
+    def __str__(self):
+        return self.name

tests/custom_lookups/tests.py

@@ -0,0 +1,279 @@
+from datetime import date
+import unittest
+
+from django.test import TestCase
+from .models import Author
+from django.db import models
+from django.db import connection
+
+
+class Div3Lookup(models.Lookup):
+    lookup_name = 'div3'
+
+    def as_sql(self, qn, connection):
+        lhs, params = self.process_lhs(qn, connection)
+        rhs, rhs_params = self.process_rhs(qn, connection)
+        params.extend(rhs_params)
+        return '%s %%%% 3 = %s' % (lhs, rhs), params
+
+
+class Div3Transform(models.Transform):
+    lookup_name = 'div3'
+
+    def as_sql(self, qn, connection):
+        lhs, lhs_params = qn.compile(self.lhs)
+        return '%s %%%% 3' % (lhs,), lhs_params
+
+
+class YearTransform(models.Transform):
+    lookup_name = 'year'
+
+    def as_sql(self, qn, connection):
+        lhs_sql, params = qn.compile(self.lhs)
+        return connection.ops.date_extract_sql('year', lhs_sql), params
+
+    @property
+    def output_type(self):
+        return models.IntegerField()
+
+
+class YearExact(models.lookups.Lookup):
+    lookup_name = 'exact'
+
+    def as_sql(self, qn, connection):
+        # We will need to skip the extract part, and instead go
+        # directly with the originating field, that is self.lhs.lhs
+        lhs_sql, lhs_params = self.process_lhs(qn, connection, self.lhs.lhs)
+        rhs_sql, rhs_params = self.process_rhs(qn, connection)
+        # Note that we must be careful so that we have params in the
+        # same order as we have the parts in the SQL.
+        params = lhs_params + rhs_params + lhs_params + rhs_params
+        # We use PostgreSQL specific SQL here. Note that we must do the
+        # conversions in SQL instead of in Python to support F() references.
+        return ("%(lhs)s >= (%(rhs)s || '-01-01')::date "
+                "AND %(lhs)s <= (%(rhs)s || '-12-31')::date" %
+                {'lhs': lhs_sql, 'rhs': rhs_sql}, params)
+YearTransform.register_lookup(YearExact)
+
+
+class YearLte(models.lookups.LessThanOrEqual):
+    """
+    The purpose of this lookup is to efficiently compare the year of the field.
+    """
+
+    def as_sql(self, qn, connection):
+        # Skip the YearTransform above us (no possibility for efficient
+        # lookup otherwise).
+        real_lhs = self.lhs.lhs
+        lhs_sql, params = self.process_lhs(qn, connection, real_lhs)
+        rhs_sql, rhs_params = self.process_rhs(qn, connection)
+        params.extend(rhs_params)
+        # Build SQL where the integer year is concatenated with last month
+        # and day, then convert that to date. (We try to have SQL like:
+        #     WHERE somecol <= '2013-12-31')
+        # but also make it work if the rhs_sql is field reference.
+        return "%s <= (%s || '-12-31')::date" % (lhs_sql, rhs_sql), params
+YearTransform.register_lookup(YearLte)
+
+
+# We will register this class temporarily in the test method.
+
+
+class InMonth(models.lookups.Lookup):
+    """
+    InMonth matches if the column's month is the same as value's month.
+    """
+    lookup_name = 'inmonth'
+
+    def as_sql(self, qn, connection):
+        lhs, lhs_params = self.process_lhs(qn, connection)
+        rhs, rhs_params = self.process_rhs(qn, connection)
+        # We need to be careful so that we get the params in right
+        # places.
+        params = lhs_params + rhs_params + lhs_params + rhs_params
+        return ("%s >= date_trunc('month', %s) and "
+                "%s < date_trunc('month', %s) + interval '1 months'" %
+                (lhs, rhs, lhs, rhs), params)
+
+
+class LookupTests(TestCase):
+    def test_basic_lookup(self):
+        a1 = Author.objects.create(name='a1', age=1)
+        a2 = Author.objects.create(name='a2', age=2)
+        a3 = Author.objects.create(name='a3', age=3)
+        a4 = Author.objects.create(name='a4', age=4)
+        models.IntegerField.register_lookup(Div3Lookup)
+        try:
+            self.assertQuerysetEqual(
+                Author.objects.filter(age__div3=0),
+                [a3], lambda x: x
+            )
+            self.assertQuerysetEqual(
+                Author.objects.filter(age__div3=1).order_by('age'),
+                [a1, a4], lambda x: x
+            )
+            self.assertQuerysetEqual(
+                Author.objects.filter(age__div3=2),
+                [a2], lambda x: x
+            )
+            self.assertQuerysetEqual(
+                Author.objects.filter(age__div3=3),
+                [], lambda x: x
+            )
+        finally:
+            models.IntegerField._unregister_lookup(Div3Lookup)
+
+    @unittest.skipUnless(connection.vendor == 'postgresql', "PostgreSQL specific SQL used")
+    def test_birthdate_month(self):
+        a1 = Author.objects.create(name='a1', birthdate=date(1981, 2, 16))
+        a2 = Author.objects.create(name='a2', birthdate=date(2012, 2, 29))
+        a3 = Author.objects.create(name='a3', birthdate=date(2012, 1, 31))
+        a4 = Author.objects.create(name='a4', birthdate=date(2012, 3, 1))
+        models.DateField.register_lookup(InMonth)
+        try:
+            self.assertQuerysetEqual(
+                Author.objects.filter(birthdate__inmonth=date(2012, 1, 15)),
+                [a3], lambda x: x
+            )
+            self.assertQuerysetEqual(
+                Author.objects.filter(birthdate__inmonth=date(2012, 2, 1)),
+                [a2], lambda x: x
+            )
+            self.assertQuerysetEqual(
+                Author.objects.filter(birthdate__inmonth=date(1981, 2, 28)),
+                [a1], lambda x: x
+            )
+            self.assertQuerysetEqual(
+                Author.objects.filter(birthdate__inmonth=date(2012, 3, 12)),
+                [a4], lambda x: x
+            )
+            self.assertQuerysetEqual(
+                Author.objects.filter(birthdate__inmonth=date(2012, 4, 1)),
+                [], lambda x: x
+            )
+        finally:
+            models.DateField._unregister_lookup(InMonth)
+
+    def test_div3_extract(self):
+        models.IntegerField.register_lookup(Div3Transform)
+        try:
+            a1 = Author.objects.create(name='a1', age=1)
+            a2 = Author.objects.create(name='a2', age=2)
+            a3 = Author.objects.create(name='a3', age=3)
+            a4 = Author.objects.create(name='a4', age=4)
+            baseqs = Author.objects.order_by('name')
+            self.assertQuerysetEqual(
+                baseqs.filter(age__div3=2),
+                [a2], lambda x: x)
+            self.assertQuerysetEqual(
+                baseqs.filter(age__div3__lte=3),
+                [a1, a2, a3, a4], lambda x: x)
+            self.assertQuerysetEqual(
+                baseqs.filter(age__div3__in=[0, 2]),
+                [a2, a3], lambda x: x)
+        finally:
+            models.IntegerField._unregister_lookup(Div3Transform)
+
+
+class YearLteTests(TestCase):
+    def setUp(self):
+        models.DateField.register_lookup(YearTransform)
+        self.a1 = Author.objects.create(name='a1', birthdate=date(1981, 2, 16))
+        self.a2 = Author.objects.create(name='a2', birthdate=date(2012, 2, 29))
+        self.a3 = Author.objects.create(name='a3', birthdate=date(2012, 1, 31))
+        self.a4 = Author.objects.create(name='a4', birthdate=date(2012, 3, 1))
+
+    def tearDown(self):
+        models.DateField._unregister_lookup(YearTransform)
+
+    @unittest.skipUnless(connection.vendor == 'postgresql', "PostgreSQL specific SQL used")
+    def test_year_lte(self):
+        baseqs = Author.objects.order_by('name')
+        self.assertQuerysetEqual(
+            baseqs.filter(birthdate__year__lte=2012),
+            [self.a1, self.a2, self.a3, self.a4], lambda x: x)
+        self.assertQuerysetEqual(
+            baseqs.filter(birthdate__year=2012),
+            [self.a2, self.a3, self.a4], lambda x: x)
+
+        self.assertNotIn('BETWEEN', str(baseqs.filter(birthdate__year=2012).query))
+        self.assertQuerysetEqual(
+            baseqs.filter(birthdate__year__lte=2011),
+            [self.a1], lambda x: x)
+        # The non-optimized version works, too.
+        self.assertQuerysetEqual(
+            baseqs.filter(birthdate__year__lt=2012),
+            [self.a1], lambda x: x)
+
+    @unittest.skipUnless(connection.vendor == 'postgresql', "PostgreSQL specific SQL used")
+    def test_year_lte_fexpr(self):
+        self.a2.age = 2011
+        self.a2.save()
+        self.a3.age = 2012
+        self.a3.save()
+        self.a4.age = 2013
+        self.a4.save()
+        baseqs = Author.objects.order_by('name')
+        self.assertQuerysetEqual(
+            baseqs.filter(birthdate__year__lte=models.F('age')),
+            [self.a3, self.a4], lambda x: x)
+        self.assertQuerysetEqual(
+            baseqs.filter(birthdate__year__lt=models.F('age')),
+            [self.a4], lambda x: x)
+
+    def test_year_lte_sql(self):
+        # This test will just check the generated SQL for __lte. This
+        # doesn't require running on PostgreSQL and spots the most likely
+        # error - not running YearLte SQL at all.
+        baseqs = Author.objects.order_by('name')
+        self.assertIn(
+            '<= (2011 || ', str(baseqs.filter(birthdate__year__lte=2011).query))
+        self.assertIn(
+            '-12-31', str(baseqs.filter(birthdate__year__lte=2011).query))
+
+    def test_postgres_year_exact(self):
+        baseqs = Author.objects.order_by('name')
+        self.assertIn(
+            '= (2011 || ', str(baseqs.filter(birthdate__year=2011).query))
+        self.assertIn(
+            '-12-31', str(baseqs.filter(birthdate__year=2011).query))
+
+    def test_custom_implementation_year_exact(self):
+        try:
+            # Two ways to add a customized implementation for different backends:
+            # First is MonkeyPatch of the class.
+            def as_custom_sql(self, qn, connection):
+                lhs_sql, lhs_params = self.process_lhs(qn, connection, self.lhs.lhs)
+                rhs_sql, rhs_params = self.process_rhs(qn, connection)
+                params = lhs_params + rhs_params + lhs_params + rhs_params
+                return ("%(lhs)s >= str_to_date(concat(%(rhs)s, '-01-01'), '%%%%Y-%%%%m-%%%%d') "
+                        "AND %(lhs)s <= str_to_date(concat(%(rhs)s, '-12-31'), '%%%%Y-%%%%m-%%%%d')" %
+                        {'lhs': lhs_sql, 'rhs': rhs_sql}, params)
+            setattr(YearExact, 'as_' + connection.vendor, as_custom_sql)
+            self.assertIn(
+                'concat(',
+                str(Author.objects.filter(birthdate__year=2012).query))
+        finally:
+            delattr(YearExact, 'as_' + connection.vendor)
+        try:
+            # The other way is to subclass the original lookup and register the subclassed
+            # lookup instead of the original.
+            class CustomYearExact(YearExact):
+                # This method should be named "as_mysql" for MySQL, "as_postgresql" for postgres
+                # and so on, but as we don't know which DB we are running on, we need to use
+                # setattr.
+                def as_custom_sql(self, qn, connection):
+                    lhs_sql, lhs_params = self.process_lhs(qn, connection, self.lhs.lhs)
+                    rhs_sql, rhs_params = self.process_rhs(qn, connection)
+                    params = lhs_params + rhs_params + lhs_params + rhs_params
+                    return ("%(lhs)s >= str_to_date(CONCAT(%(rhs)s, '-01-01'), '%%%%Y-%%%%m-%%%%d') "
+                            "AND %(lhs)s <= str_to_date(CONCAT(%(rhs)s, '-12-31'), '%%%%Y-%%%%m-%%%%d')" %
+                            {'lhs': lhs_sql, 'rhs': rhs_sql}, params)
+            setattr(CustomYearExact, 'as_' + connection.vendor, CustomYearExact.as_custom_sql)
+            YearTransform.register_lookup(CustomYearExact)
+            self.assertIn(
+                'CONCAT(',
+                str(Author.objects.filter(birthdate__year=2012).query))
+        finally:
+            YearTransform._unregister_lookup(CustomYearExact)
+            YearTransform.register_lookup(YearExact)

tests/expressions/tests.py

@@ -3,7 +3,7 @@ from __future__ import unicode_literals
 from django.core.exceptions import FieldError
 from django.db.models import F
 from django.db import transaction
-from django.test import TestCase
+from django.test import TestCase, skipIfDBFeature
 from django.utils import six
 
 from .models import Company, Employee
@@ -224,6 +224,25 @@ class ExpressionsTests(TestCase):
         acme.num_employees = F("num_employees") + 16
         self.assertRaises(TypeError, acme.save)
 
+    def test_ticket_11722_iexact_lookup(self):
+        Employee.objects.create(firstname="John", lastname="Doe")
+        Employee.objects.create(firstname="Test", lastname="test")
+
+        queryset = Employee.objects.filter(firstname__iexact=F('lastname'))
+        self.assertQuerysetEqual(queryset, ["<Employee: Test test>"])
+
+    @skipIfDBFeature('has_case_insensitive_like')
+    def test_ticket_16731_startswith_lookup(self):
+        Employee.objects.create(firstname="John", lastname="Doe")
+        e2 = Employee.objects.create(firstname="Jack", lastname="Jackson")
+        e3 = Employee.objects.create(firstname="Jack", lastname="jackson")
+        self.assertQuerysetEqual(
+            Employee.objects.filter(lastname__startswith=F('firstname')),
+            [e2], lambda x: x)
+        self.assertQuerysetEqual(
+            Employee.objects.filter(lastname__istartswith=F('firstname')).order_by('pk'),
+            [e2, e3], lambda x: x)
+
     def test_ticket_18375_join_reuse(self):
         # Test that reverse multijoin F() references and the lookup target
         # the same join. Pre #18375 the F() join was generated first, and the

tests/null_queries/tests.py

@@ -45,9 +45,6 @@ class NullQueriesTests(TestCase):
         # Can't use None on anything other than __exact and __iexact
         self.assertRaises(ValueError, Choice.objects.filter, id__gt=None)
 
-        # Can't use None on anything other than __exact and __iexact
-        self.assertRaises(ValueError, Choice.objects.filter, foo__gt=None)
-
         # Related managers use __exact=None implicitly if the object hasn't been saved.
         p2 = Poll(question="How?")
         self.assertEqual(repr(p2.choice_set.all()), '[]')

tests/queries/tests.py

@@ -2632,8 +2632,15 @@ class WhereNodeTest(TestCase):
         def as_sql(self, qn, connection):
             return 'dummy', []
 
+    class MockCompiler(object):
+        def compile(self, node):
+            return node.as_sql(self, connection)
+
+        def __call__(self, name):
+            return connection.ops.quote_name(name)
+
     def test_empty_full_handling_conjunction(self):
-        qn = connection.ops.quote_name
+        qn = WhereNodeTest.MockCompiler()
         w = WhereNode(children=[EverythingNode()])
         self.assertEqual(w.as_sql(qn, connection), ('', []))
         w.negate()
@@ -2658,7 +2665,7 @@ class WhereNodeTest(TestCase):
         self.assertEqual(w.as_sql(qn, connection), ('', []))
 
     def test_empty_full_handling_disjunction(self):
-        qn = connection.ops.quote_name
+        qn = WhereNodeTest.MockCompiler()
         w = WhereNode(children=[EverythingNode()], connector='OR')
         self.assertEqual(w.as_sql(qn, connection), ('', []))
         w.negate()
@@ -2685,7 +2692,7 @@ class WhereNodeTest(TestCase):
         self.assertEqual(w.as_sql(qn, connection), ('NOT (dummy)', []))
 
     def test_empty_nodes(self):
-        qn = connection.ops.quote_name
+        qn = WhereNodeTest.MockCompiler()
         empty_w = WhereNode()
         w = WhereNode(children=[empty_w, empty_w])
         self.assertEqual(w.as_sql(qn, connection), (None, []))