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Add documentation for the delete_rule argument.

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Vincent Driessen 2010-12-20 05:23:27 -08:00
parent e05e6b89f3
commit 52f5deb456
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docs/guide/defining-documents.rst
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@ -193,6 +193,37 @@ as the constructor's argument::
class ProfilePage(Document):
content = StringField()
Dealing with deletion of referred documents
'''''''''''''''''''''''''''''''''''''''''''
By default, MongoDB doesn't check the integrity of your data, so deleting
documents that other documents still hold references to will lead to consistency
issues. Mongoengine's :class:`ReferenceField` adds some functionality to
safeguard against these kinds of database integrity problems, providing each
reference with a delete rule specification. A delete rule is specified by
supplying the :attr:`delete_rule` attribute on the :class:`ReferenceField`
definition, like this::
class Employee(Document):
...
profile_page = ReferenceField('ProfilePage', delete_rule=mongoengine.NULLIFY)
Its value can take any of the following constants:
:const:`mongoengine.DO_NOTHING`
This is the default and won't do anything. Deletes are fast, but may
cause database inconsistency or dangling references.
:const:`mongoengine.DENY`
Deletion is denied if there still exist references to the object being
deleted.
:const:`mongoengine.NULLIFY`
Any object's fields still referring to the object being deleted are
removed (using MongoDB's "unset" operation), effectively nullifying the
relationship.
:const:`mongoengine.CASCADE`
Any object containing fields that are refererring to the object being
deleted are deleted first.
Generic reference fields
''''''''''''''''''''''''
A second kind of reference field also exists,