# Django 2.2.9.dev20191202104323 文档

# Django Exceptions

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

## 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 app loading process, which initializes the ORM, is complete.

### `ObjectDoesNotExist`

exception `ObjectDoesNotExist`

  The base class for `DoesNotExist` exceptions; a `try/except` for `ObjectDoesNotExist` will catch `DoesNotExist` exceptions for all models.

  See `get()` for further information on `ObjectDoesNotExist` and `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 `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 `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 `get()` for further information.

### `SuspiciousOperation`

exception `SuspiciousOperation`

  The `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 `HttpResponseBadRequest`. See the logging documentation for more information.

### `PermissionDenied`

exception `PermissionDenied`

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

### `ViewDoesNotExist`

exception `ViewDoesNotExist`

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

### `MiddlewareNotUsed`

exception `MiddlewareNotUsed`

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

### `ImproperlyConfigured`

exception `ImproperlyConfigured`

  The `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 `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 `ValidationError` exception is raised when data fails form or model field validation. For more information about validation, see Form and Field Validation, Model Field Validation and the Validator Reference.

#### `NON_FIELD_ERRORS`

`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.

## URL Resolver exceptions

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

### `Resolver404`

exception `Resolver404`

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

### `NoReverseMatch`

exception `NoReverseMatch`

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

## 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 `django.db.models.PROTECT`. `models.ProtectedError` is a subclass of `IntegrityError`.

## Http Exceptions

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

### `UnreadablePostError`

exception `UnreadablePostError`

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

## Transaction Exceptions

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

### `TransactionManagementError`

exception `TransactionManagementError`

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

## Testing Framework Exceptions

Exceptions provided by the `django.test` package.

### `RedirectCycleError`

exception `client.``RedirectCycleError`

  `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 Built-in Exceptions.