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646 lines
19 KiB
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646 lines
19 KiB
Plaintext
=======
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Signals
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=======
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A list of all the signals that Django sends. All built-in signals are sent
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using the :meth:`~django.dispatch.Signal.send` method.
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.. seealso::
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See the documentation on the :doc:`signal dispatcher </topics/signals>` for
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information regarding how to register for and receive signals.
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The :doc:`authentication framework </topics/auth/index>` sends :ref:`signals when
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a user is logged in / out <topics-auth-signals>`.
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Model signals
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=============
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.. module:: django.db.models.signals
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:synopsis: Signals sent by the model system.
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The :mod:`django.db.models.signals` module defines a set of signals sent by the
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model system.
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.. warning::
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Many of these signals are sent by various model methods like
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``__init__()`` or :meth:`~django.db.models.Model.save` that you can
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override in your own code.
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If you override these methods on your model, you must call the parent class'
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methods for this signals to be sent.
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Note also that Django stores signal handlers as weak references by default,
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so if your handler is a local function, it may be garbage collected. To
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prevent this, pass ``weak=False`` when you call the signal's :meth:`~django.dispatch.Signal.connect`.
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.. note::
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Model signals ``sender`` model can be lazily referenced when connecting a
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receiver by specifying its full application label. For example, an
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``Answer`` model defined in the ``polls`` application could be referenced
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as ``'polls.Answer'``. This sort of reference can be quite handy when
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dealing with circular import dependencies and swappable models.
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``pre_init``
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------------
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.. attribute:: django.db.models.signals.pre_init
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:module:
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.. ^^^^^^^ this :module: hack keeps Sphinx from prepending the module.
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Whenever you instantiate a Django model, this signal is sent at the beginning
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of the model's ``__init__()`` method.
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Arguments sent with this signal:
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``sender``
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The model class that just had an instance created.
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``args``
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A list of positional arguments passed to ``__init__()``:
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``kwargs``
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A dictionary of keyword arguments passed to ``__init__()``:
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For example, the :doc:`tutorial </intro/tutorial01>` has this line::
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p = Poll(question="What's up?", pub_date=datetime.now())
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The arguments sent to a :data:`pre_init` handler would be:
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========== ===============================================================
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Argument Value
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========== ===============================================================
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``sender`` ``Poll`` (the class itself)
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``args`` ``[]`` (an empty list because there were no positional
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arguments passed to ``__init__()``.)
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``kwargs`` ``{'question': "What's up?", 'pub_date': datetime.now()}``
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========== ===============================================================
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``post_init``
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-------------
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.. data:: django.db.models.signals.post_init
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:module:
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Like pre_init, but this one is sent when the ``__init__()`` method finishes.
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Arguments sent with this signal:
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``sender``
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As above: the model class that just had an instance created.
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``instance``
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The actual instance of the model that's just been created.
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``pre_save``
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------------
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.. data:: django.db.models.signals.pre_save
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:module:
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This is sent at the beginning of a model's :meth:`~django.db.models.Model.save`
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method.
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Arguments sent with this signal:
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``sender``
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The model class.
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``instance``
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The actual instance being saved.
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``raw``
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A boolean; ``True`` if the model is saved exactly as presented
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(i.e. when loading a fixture). One should not query/modify other
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records in the database as the database might not be in a
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consistent state yet.
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``using``
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The database alias being used.
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``update_fields``
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The set of fields to update as passed to :meth:`.Model.save`, or ``None``
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if ``update_fields`` wasn't passed to ``save()``.
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``post_save``
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-------------
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.. data:: django.db.models.signals.post_save
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:module:
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Like :data:`pre_save`, but sent at the end of the
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:meth:`~django.db.models.Model.save` method.
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Arguments sent with this signal:
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``sender``
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The model class.
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``instance``
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The actual instance being saved.
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``created``
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A boolean; ``True`` if a new record was created.
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``raw``
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A boolean; ``True`` if the model is saved exactly as presented
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(i.e. when loading a fixture). One should not query/modify other
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records in the database as the database might not be in a
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consistent state yet.
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``using``
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The database alias being used.
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``update_fields``
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The set of fields to update as passed to :meth:`.Model.save`, or ``None``
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if ``update_fields`` wasn't passed to ``save()``.
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``pre_delete``
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--------------
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.. data:: django.db.models.signals.pre_delete
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:module:
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Sent at the beginning of a model's :meth:`~django.db.models.Model.delete`
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method and a queryset's :meth:`~django.db.models.query.QuerySet.delete` method.
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Arguments sent with this signal:
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``sender``
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The model class.
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``instance``
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The actual instance being deleted.
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``using``
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The database alias being used.
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``post_delete``
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---------------
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.. data:: django.db.models.signals.post_delete
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:module:
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Like :data:`pre_delete`, but sent at the end of a model's
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:meth:`~django.db.models.Model.delete` method and a queryset's
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:meth:`~django.db.models.query.QuerySet.delete` method.
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Arguments sent with this signal:
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``sender``
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The model class.
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``instance``
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The actual instance being deleted.
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Note that the object will no longer be in the database, so be very
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careful what you do with this instance.
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``using``
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The database alias being used.
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``m2m_changed``
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---------------
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.. data:: django.db.models.signals.m2m_changed
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:module:
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Sent when a :class:`~django.db.models.ManyToManyField` is changed on a model
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instance. Strictly speaking, this is not a model signal since it is sent by the
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:class:`~django.db.models.ManyToManyField`, but since it complements the
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:data:`pre_save`/:data:`post_save` and :data:`pre_delete`/:data:`post_delete`
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when it comes to tracking changes to models, it is included here.
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Arguments sent with this signal:
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``sender``
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The intermediate model class describing the
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:class:`~django.db.models.ManyToManyField`. This class is automatically
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created when a many-to-many field is defined; you can access it using the
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``through`` attribute on the many-to-many field.
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``instance``
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The instance whose many-to-many relation is updated. This can be an
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instance of the ``sender``, or of the class the
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:class:`~django.db.models.ManyToManyField` is related to.
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``action``
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A string indicating the type of update that is done on the relation.
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This can be one of the following:
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``"pre_add"``
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Sent *before* one or more objects are added to the relation.
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``"post_add"``
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Sent *after* one or more objects are added to the relation.
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``"pre_remove"``
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Sent *before* one or more objects are removed from the relation.
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``"post_remove"``
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Sent *after* one or more objects are removed from the relation.
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``"pre_clear"``
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Sent *before* the relation is cleared.
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``"post_clear"``
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Sent *after* the relation is cleared.
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``reverse``
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Indicates which side of the relation is updated (i.e., if it is the
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forward or reverse relation that is being modified).
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``model``
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The class of the objects that are added to, removed from or cleared
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from the relation.
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``pk_set``
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For the ``pre_add``, ``post_add``, ``pre_remove`` and ``post_remove``
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actions, this is a set of primary key values that have been added to
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or removed from the relation.
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For the ``pre_clear`` and ``post_clear`` actions, this is ``None``.
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``using``
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The database alias being used.
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For example, if a ``Pizza`` can have multiple ``Topping`` objects, modeled
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like this::
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class Topping(models.Model):
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# ...
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pass
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class Pizza(models.Model):
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# ...
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toppings = models.ManyToManyField(Topping)
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If we connected a handler like this::
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from django.db.models.signals import m2m_changed
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def toppings_changed(sender, **kwargs):
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# Do something
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pass
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m2m_changed.connect(toppings_changed, sender=Pizza.toppings.through)
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and then did something like this::
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>>> p = Pizza.objects.create(...)
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>>> t = Topping.objects.create(...)
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>>> p.toppings.add(t)
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the arguments sent to a :data:`m2m_changed` handler (``toppings_changed`` in
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the example above) would be:
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============== ============================================================
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Argument Value
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============== ============================================================
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``sender`` ``Pizza.toppings.through`` (the intermediate m2m class)
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``instance`` ``p`` (the ``Pizza`` instance being modified)
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``action`` ``"pre_add"`` (followed by a separate signal with ``"post_add"``)
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``reverse`` ``False`` (``Pizza`` contains the
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:class:`~django.db.models.ManyToManyField`, so this call
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modifies the forward relation)
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``model`` ``Topping`` (the class of the objects added to the
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``Pizza``)
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``pk_set`` ``{t.id}`` (since only ``Topping t`` was added to the relation)
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``using`` ``"default"`` (since the default router sends writes here)
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============== ============================================================
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And if we would then do something like this::
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>>> t.pizza_set.remove(p)
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the arguments sent to a :data:`m2m_changed` handler would be:
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============== ============================================================
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Argument Value
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============== ============================================================
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``sender`` ``Pizza.toppings.through`` (the intermediate m2m class)
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``instance`` ``t`` (the ``Topping`` instance being modified)
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``action`` ``"pre_remove"`` (followed by a separate signal with ``"post_remove"``)
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``reverse`` ``True`` (``Pizza`` contains the
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:class:`~django.db.models.ManyToManyField`, so this call
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modifies the reverse relation)
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``model`` ``Pizza`` (the class of the objects removed from the
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``Topping``)
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``pk_set`` ``{p.id}`` (since only ``Pizza p`` was removed from the
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relation)
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``using`` ``"default"`` (since the default router sends writes here)
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============== ============================================================
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``class_prepared``
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------------------
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.. data:: django.db.models.signals.class_prepared
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:module:
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Sent whenever a model class has been "prepared" -- that is, once model has
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been defined and registered with Django's model system. Django uses this
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signal internally; it's not generally used in third-party applications.
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Since this signal is sent during the app registry population process, and
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:meth:`AppConfig.ready() <django.apps.AppConfig.ready>` runs after the app
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registry is fully populated, receivers cannot be connected in that method.
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One possibility is to connect them ``AppConfig.__init__()`` instead, taking
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care not to import models or trigger calls to the app registry.
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Arguments that are sent with this signal:
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``sender``
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The model class which was just prepared.
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Management signals
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==================
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Signals sent by :doc:`django-admin </ref/django-admin>`.
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``pre_migrate``
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---------------
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.. data:: django.db.models.signals.pre_migrate
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:module:
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Sent by the :djadmin:`migrate` command before it starts to install an
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application. It's not emitted for applications that lack a ``models`` module.
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Arguments sent with this signal:
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``sender``
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An :class:`~django.apps.AppConfig` instance for the application about to
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be migrated/synced.
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``app_config``
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Same as ``sender``.
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``verbosity``
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Indicates how much information manage.py is printing on screen. See
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the :option:`--verbosity` flag for details.
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Functions which listen for :data:`pre_migrate` should adjust what they
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output to the screen based on the value of this argument.
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``interactive``
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If ``interactive`` is ``True``, it's safe to prompt the user to input
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things on the command line. If ``interactive`` is ``False``, functions
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which listen for this signal should not try to prompt for anything.
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For example, the :mod:`django.contrib.auth` app only prompts to create a
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superuser when ``interactive`` is ``True``.
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``using``
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The alias of database on which a command will operate.
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``plan``
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The migration plan that is going to be used for the migration run. While
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the plan is not public API, this allows for the rare cases when it is
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necessary to know the plan. A plan is a list of two-tuples with the first
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item being the instance of a migration class and the second item showing
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if the migration was rolled back (``True``) or applied (``False``).
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``apps``
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An instance of :data:`Apps <django.apps>` containing the state of the
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project before the migration run. It should be used instead of the global
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:attr:`apps <django.apps.apps>` registry to retrieve the models you
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want to perform operations on.
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``post_migrate``
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----------------
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.. data:: django.db.models.signals.post_migrate
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:module:
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Sent at the end of the :djadmin:`migrate` (even if no migrations are run) and
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:djadmin:`flush` commands. It's not emitted for applications that lack a
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``models`` module.
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Handlers of this signal must not perform database schema alterations as doing
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so may cause the :djadmin:`flush` command to fail if it runs during the
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:djadmin:`migrate` command.
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Arguments sent with this signal:
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``sender``
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An :class:`~django.apps.AppConfig` instance for the application that was
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just installed.
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``app_config``
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Same as ``sender``.
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``verbosity``
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Indicates how much information manage.py is printing on screen. See
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the :option:`--verbosity` flag for details.
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Functions which listen for :data:`post_migrate` should adjust what they
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output to the screen based on the value of this argument.
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``interactive``
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If ``interactive`` is ``True``, it's safe to prompt the user to input
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things on the command line. If ``interactive`` is ``False``, functions
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which listen for this signal should not try to prompt for anything.
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For example, the :mod:`django.contrib.auth` app only prompts to create a
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superuser when ``interactive`` is ``True``.
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``using``
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The database alias used for synchronization. Defaults to the ``default``
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database.
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``plan``
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The migration plan that was used for the migration run. While the plan is
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not public API, this allows for the rare cases when it is necessary to
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know the plan. A plan is a list of two-tuples with the first item being
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the instance of a migration class and the second item showing if the
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migration was rolled back (``True``) or applied (``False``).
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``apps``
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An instance of :data:`Apps <django.apps.apps>` containing the state of the
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project after the migration run. It should be used instead of the global
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:attr:`apps <django.apps.apps>` registry to retrieve the models you
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want to perform operations on.
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For example, you could register a callback in an
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:class:`~django.apps.AppConfig` like this::
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from django.apps import AppConfig
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from django.db.models.signals import post_migrate
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def my_callback(sender, **kwargs):
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# Your specific logic here
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pass
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class MyAppConfig(AppConfig):
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...
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def ready(self):
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post_migrate.connect(my_callback, sender=self)
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.. note::
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If you provide an :class:`~django.apps.AppConfig` instance as the sender
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argument, please ensure that the signal is registered in
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:meth:`~django.apps.AppConfig.ready`. ``AppConfig``\s are recreated for
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tests that run with a modified set of :setting:`INSTALLED_APPS` (such as
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when settings are overridden) and such signals should be connected for each
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new ``AppConfig`` instance.
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Request/response signals
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========================
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.. module:: django.core.signals
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:synopsis: Core signals sent by the request/response system.
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Signals sent by the core framework when processing a request.
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``request_started``
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-------------------
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.. data:: django.core.signals.request_started
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:module:
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Sent when Django begins processing an HTTP request.
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Arguments sent with this signal:
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``sender``
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The handler class -- e.g. ``django.core.handlers.wsgi.WsgiHandler`` -- that
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handled the request.
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``environ``
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The ``environ`` dictionary provided to the request.
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``request_finished``
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--------------------
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.. data:: django.core.signals.request_finished
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:module:
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Sent when Django finishes delivering an HTTP response to the client.
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Arguments sent with this signal:
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``sender``
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The handler class, as above.
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``got_request_exception``
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-------------------------
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.. data:: django.core.signals.got_request_exception
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:module:
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This signal is sent whenever Django encounters an exception while processing an incoming HTTP request.
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Arguments sent with this signal:
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``sender``
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The handler class, as above.
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``request``
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The :class:`~django.http.HttpRequest` object.
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Test signals
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============
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.. module:: django.test.signals
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:synopsis: Signals sent during testing.
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Signals only sent when :ref:`running tests <running-tests>`.
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``setting_changed``
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-------------------
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.. data:: django.test.signals.setting_changed
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:module:
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This signal is sent when the value of a setting is changed through the
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``django.test.TestCase.settings()`` context manager or the
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:func:`django.test.override_settings` decorator/context manager.
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It's actually sent twice: when the new value is applied ("setup") and when the
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original value is restored ("teardown"). Use the ``enter`` argument to
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distinguish between the two.
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You can also import this signal from ``django.core.signals`` to avoid importing
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from ``django.test`` in non-test situations.
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Arguments sent with this signal:
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``sender``
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The settings handler.
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``setting``
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The name of the setting.
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``value``
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The value of the setting after the change. For settings that initially
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don't exist, in the "teardown" phase, ``value`` is ``None``.
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``enter``
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A boolean; ``True`` if the setting is applied, ``False`` if restored.
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``template_rendered``
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---------------------
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.. data:: django.test.signals.template_rendered
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:module:
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Sent when the test system renders a template. This signal is not emitted during
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normal operation of a Django server -- it is only available during testing.
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Arguments sent with this signal:
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``sender``
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The :class:`~django.template.Template` object which was rendered.
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``template``
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Same as sender
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``context``
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The :class:`~django.template.Context` with which the template was
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rendered.
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Database Wrappers
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=================
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.. module:: django.db.backends
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:synopsis: Core signals sent by the database wrapper.
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Signals sent by the database wrapper when a database connection is
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initiated.
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``connection_created``
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----------------------
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.. data:: django.db.backends.signals.connection_created
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:module:
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Sent when the database wrapper makes the initial connection to the
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database. This is particularly useful if you'd like to send any post
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connection commands to the SQL backend.
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Arguments sent with this signal:
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``sender``
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The database wrapper class -- i.e.
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``django.db.backends.postgresql.DatabaseWrapper`` or
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``django.db.backends.mysql.DatabaseWrapper``, etc.
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``connection``
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The database connection that was opened. This can be used in a
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multiple-database configuration to differentiate connection signals
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from different databases.
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