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[1.5.x] Fixed #17528 -- Documented that add() and remove() with a man…

…y-to-many relationship do not call Model.save()

Backport of 3cdeb57 from master
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commit 61c8c1b6dcd267a7d4777ff3b0a78eaedb9b95d3 1 parent 80a7dd6
@timgraham timgraham authored
Showing with 16 additions and 0 deletions.
  1. +16 −0 docs/ref/models/relations.txt
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16 docs/ref/models/relations.txt
@@ -44,6 +44,14 @@ Related objects reference
>>> e = Entry.objects.get(id=234)
>>> b.entry_set.add(e) # Associates Entry e with Blog b.
+ In the example above, ``e.save()`` is called to perform the update.
+ Using ``add()`` with a many-to-many relationship, however, will not
+ call any ``save()`` methods, but rather create the relationships
+ using :meth:`QuerySet.bulk_create()
+ <django.db.models.query.QuerySet.bulk_create>`. If you need to execute
+ some custom logic when a relationship is created, listen to the
+ :data:`~django.db.models.signals.m2m_changed` signal.
+
.. method:: create(**kwargs)
Creates a new object, saves it and puts it in the related object set.
@@ -82,6 +90,14 @@ Related objects reference
>>> e = Entry.objects.get(id=234)
>>> b.entry_set.remove(e) # Disassociates Entry e from Blog b.
+ Similar to :meth:`add()`, ``e.save()`` is called in the example above
+ to perform the update. Using ``remove()`` with a many-to-many
+ relationship, however, will delete the relationships using
+ :meth:`QuerySet.delete()<django.db.models.query.QuerySet.delete>` which
+ means no model ``save()`` methods are called; listen to the
+ :data:`~django.db.models.signals.m2m_changed` signal if you wish to
+ execute custom code when a relationship is deleted.
+
For :class:`~django.db.models.ForeignKey` objects, this method only
exists if ``null=True``. If the related field can't be set to ``None``
(``NULL``), then an object can't be removed from a relation without
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