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:`Model.DoesNotExist
<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()`.
``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.
``FullResultSet``
-----------------
.. exception:: FullResultSet
``FullResultSet`` may be raised during query generation if a query will
match everything. 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 base class for :exc:`Model.MultipleObjectsReturned
<django.db.models.Model.MultipleObjectsReturned>` exceptions. A
``try/except`` for ``MultipleObjectsReturned`` will catch
:exc:`~django.db.models.Model.MultipleObjectsReturned` exceptions for all
models.
See :meth:`~django.db.models.query.QuerySet.get()`.
``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``
* ``TooManyFilesSent``
If a ``SuspiciousOperation`` exception reaches the ASGI/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.
``BadRequest``
--------------
.. exception:: BadRequest
The :exc:`BadRequest` exception is raised when the request cannot be
processed due to a client error. If a ``BadRequest`` exception reaches the
ASGI/WSGI handler level it results in a
:class:`~django.http.HttpResponseBadRequest`.
``RequestAborted``
------------------
.. exception:: RequestAborted
The :exc:`RequestAborted` exception is raised when an 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
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 :func:`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`.
.. exception:: models.RestrictedError
Raised to prevent deletion of referenced objects when using
:attr:`django.db.models.RESTRICT`. :exc:`models.RestrictedError` 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.
.. currentmodule:: django.contrib.sessions.exceptions
Sessions Exceptions
===================
Sessions exceptions are defined in ``django.contrib.sessions.exceptions``.
``SessionInterrupted``
----------------------
.. exception:: SessionInterrupted
:exc:`SessionInterrupted` is raised when a session is destroyed in a
concurrent request. It's a subclass of
:exc:`~django.core.exceptions.BadRequest`.
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`.