django/docs/ref/exceptions.txt

=================
Django Exceptions
=================

Django raises some of its own exceptions as well as standard Python exceptions.

Django Core Exceptions
======================

.. module:: django.core.exceptions
    :synopsis: Django core exceptions

Django core exception classes are defined in ``django.core.exceptions``.

``AppRegistryNotReady``
-----------------------

.. exception:: AppRegistryNotReady

    This exception is raised when attempting to use models before the :ref:`app
    loading process <app-loading-process>`, which initializes the ORM, is
    complete.

``ObjectDoesNotExist``
----------------------

.. exception:: ObjectDoesNotExist

    The base class for :exc:`~django.db.models.Model.DoesNotExist` exceptions;
    a ``try/except`` for ``ObjectDoesNotExist`` will catch
    :exc:`~django.db.models.Model.DoesNotExist` exceptions for all models.

    See :meth:`~django.db.models.query.QuerySet.get()` for further information
    on :exc:`ObjectDoesNotExist` and :exc:`~django.db.models.Model.DoesNotExist`.

``EmptyResultSet``
------------------

.. exception:: EmptyResultSet

    ``EmptyResultSet`` may be raised during query generation if a query won't
    return any results. Most Django projects won't encounter this exception,
    but it might be useful for implementing custom lookups and expressions.

``FieldDoesNotExist``
---------------------

.. exception:: FieldDoesNotExist

    The ``FieldDoesNotExist`` exception is raised by a model's
    ``_meta.get_field()`` method when the requested field does not exist on the
    model or on the model's parents.

``MultipleObjectsReturned``
---------------------------

.. exception:: MultipleObjectsReturned

    The :exc:`MultipleObjectsReturned` exception is raised by a query if only
    one object is expected, but multiple objects are returned. A base version
    of this exception is provided in :mod:`django.core.exceptions`; each model
    class contains a subclassed version that can be used to identify the
    specific object type that has returned multiple objects.

    See :meth:`~django.db.models.query.QuerySet.get()` for further information.

``SuspiciousOperation``
-----------------------

.. exception:: SuspiciousOperation

    The :exc:`SuspiciousOperation` exception is raised when a user has
    performed an operation that should be considered suspicious from a security
    perspective, such as tampering with a session cookie. Subclasses of
    ``SuspiciousOperation`` include:

    * ``DisallowedHost``
    * ``DisallowedModelAdminLookup``
    * ``DisallowedModelAdminToField``
    * ``DisallowedRedirect``
    * ``InvalidSessionKey``
    * ``RequestDataTooBig``
    * ``SuspiciousFileOperation``
    * ``SuspiciousMultipartForm``
    * ``SuspiciousSession``
    * ``TooManyFieldsSent``

    If a ``SuspiciousOperation`` exception reaches the WSGI handler level it is
    logged at the ``Error`` level and results in
    a :class:`~django.http.HttpResponseBadRequest`. See the :doc:`logging
    documentation </topics/logging/>` for more information.

``PermissionDenied``
--------------------

.. exception:: PermissionDenied

    The :exc:`PermissionDenied` exception is raised when a user does not have
    permission to perform the action requested.

``ViewDoesNotExist``
--------------------

.. exception:: ViewDoesNotExist

    The :exc:`ViewDoesNotExist` exception is raised by
    :mod:`django.urls` when a requested view does not exist.

``MiddlewareNotUsed``
---------------------

.. exception:: MiddlewareNotUsed

    The :exc:`MiddlewareNotUsed` exception is raised when a middleware is not
    used in the server configuration.

``ImproperlyConfigured``
------------------------

.. exception:: ImproperlyConfigured

    The :exc:`ImproperlyConfigured` exception is raised when Django is
    somehow improperly configured -- for example, if a value in ``settings.py``
    is incorrect or unparseable.

``FieldError``
--------------

.. exception:: FieldError

    The :exc:`FieldError` exception is raised when there is a problem with a
    model field. This can happen for several reasons:

    - A field in a model clashes with a field of the same name from an
      abstract base class
    - An infinite loop is caused by ordering
    - A keyword cannot be parsed from the filter parameters
    - A field cannot be determined from a keyword in the query
      parameters
    - A join is not permitted on the specified field
    - A field name is invalid
    - A query contains invalid order_by arguments

``ValidationError``
-------------------

.. exception:: ValidationError

    The :exc:`ValidationError` exception is raised when data fails form or
    model field validation. For more information about validation, see
    :doc:`Form and Field Validation </ref/forms/validation>`,
    :ref:`Model Field Validation <validating-objects>` and the
    :doc:`Validator Reference </ref/validators>`.

``NON_FIELD_ERRORS``
~~~~~~~~~~~~~~~~~~~~

.. data:: NON_FIELD_ERRORS

``ValidationError``\s that don't belong to a particular field in a form
or model are classified as ``NON_FIELD_ERRORS``. This constant is used
as a key in dictionaries that otherwise map fields to their respective
list of errors.

``RequestAborted``
------------------

.. exception:: RequestAborted

    .. versionadded:: 3.0

    The :exc:`RequestAborted` exception is raised when a HTTP body being read
    in by the handler is cut off midstream and the client connection closes,
    or when the client does not send data and hits a timeout where the server
    closes the connection.

    It is internal to the HTTP handler modules and you are unlikely to see
    it elsewhere. If you are modifying HTTP handling code, you should raise
    this when you encounter an aborted request to make sure the socket is
    closed cleanly.

``SynchronousOnlyOperation``
----------------------------

.. exception:: SynchronousOnlyOperation

    .. versionadded:: 3.0

    The :exc:`SynchronousOnlyOperation` exception is raised when code that
    is only allowed in synchronous Python code is called from an asynchronous
    context (a thread with a running asynchronous event loop). These parts of
    Django are generally heavily reliant on thread-safety to function and don't
    work correctly under coroutines sharing the same thread.

    If you are trying to call code that is synchronous-only from an
    asynchronous thread, then create a synchronous thread and call it in that.
    You can accomplish this is with ``asgiref.sync.sync_to_async``.

.. currentmodule:: django.urls

URL Resolver exceptions
=======================

URL Resolver exceptions are defined in ``django.urls``.

``Resolver404``
---------------

.. exception:: Resolver404

    The :exc:`Resolver404` exception is raised by
    :func:`~django.urls.resolve()` if the path passed to ``resolve()`` doesn't
    map to a view. It's a subclass of :class:`django.http.Http404`.

``NoReverseMatch``
------------------

.. exception:: NoReverseMatch

    The :exc:`NoReverseMatch` exception is raised by :mod:`django.urls` when a
    matching URL in your URLconf cannot be identified based on the parameters
    supplied.

.. currentmodule:: django.db

Database Exceptions
===================

Database exceptions may be imported from ``django.db``.

Django wraps the standard database exceptions so that your Django code has a
guaranteed common implementation of these classes.

.. exception:: Error
.. exception:: InterfaceError
.. exception:: DatabaseError
.. exception:: DataError
.. exception:: OperationalError
.. exception:: IntegrityError
.. exception:: InternalError
.. exception:: ProgrammingError
.. exception:: NotSupportedError

The Django wrappers for database exceptions behave exactly the same as
the underlying database exceptions. See :pep:`249`, the Python Database API
Specification v2.0, for further information.

As per :pep:`3134`, a ``__cause__`` attribute is set with the original
(underlying) database exception, allowing access to any additional
information provided.

.. exception:: models.ProtectedError

Raised to prevent deletion of referenced objects when using
:attr:`django.db.models.PROTECT`. :exc:`models.ProtectedError` is a subclass
of :exc:`IntegrityError`.

.. currentmodule:: django.http

Http Exceptions
===============

Http exceptions may be imported from ``django.http``.

``UnreadablePostError``
-----------------------

.. exception:: UnreadablePostError

    :exc:`UnreadablePostError` is raised when a user cancels an upload.

Transaction Exceptions
======================

.. currentmodule:: django.db.transaction

Transaction exceptions are defined in ``django.db.transaction``.

``TransactionManagementError``
------------------------------

.. exception:: TransactionManagementError

    :exc:`TransactionManagementError` is raised for any and all problems
    related to database transactions.

.. currentmodule:: django.test

Testing Framework Exceptions
============================

Exceptions provided by the ``django.test`` package.

``RedirectCycleError``
----------------------

.. exception:: client.RedirectCycleError

    :exc:`~client.RedirectCycleError` is raised when the test client detects a
    loop or an overly long chain of redirects.

Python Exceptions
=================

Django raises built-in Python exceptions when appropriate as well. See the
Python documentation for further information on the :ref:`bltin-exceptions`.