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Code Issues 25 Releases Wiki Activity

Fixed #30828 -- Added how to remove/insert many-to-many relations in bulk to the database optimization docs.

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David Foster 2019-10-20 11:47:38 -07:00 committed by Mariusz Felisiak
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AUTHORS
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@ -231,6 +231,7 @@ answer newbie questions, and generally made Django that much better:
David Cramer <dcramer@gmail.com>
David Danier <david.danier@team23.de>
David Eklund
David Foster <david@dafoster.net>
David Gouldin <dgouldin@gmail.com>
david@kazserve.org
David Krauth

62
docs/topics/db/optimization.txt
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@ -410,3 +410,65 @@ objects to reduce the number of SQL queries. For example::
my_band.members.add(my_friend)
...where ``Bands`` and ``Artists`` have a many-to-many relationship.
When inserting different pairs of objects into
:class:`~django.db.models.ManyToManyField` or when the custom
:attr:`~django.db.models.ManyToManyField.through` table is defined, use
:meth:`~django.db.models.query.QuerySet.bulk_create()` method to reduce the
number of SQL queries. For example::
PizzaToppingRelationship = Pizza.toppings.through
PizzaToppingRelationship.objects.bulk_create([
PizzaToppingRelationship(pizza=my_pizza, topping=pepperoni),
PizzaToppingRelationship(pizza=your_pizza, topping=pepperoni),
PizzaToppingRelationship(pizza=your_pizza, topping=mushroom),
], ignore_conflicts=True)
...is preferable to::
my_pizza.toppings.add(pepperoni)
your_pizza.toppings.add(pepperoni, mushroom)
...where ``Pizza`` and ``Topping`` have a many-to-many relationship. Note that
there are a number of :meth:`caveats to this method
<django.db.models.query.QuerySet.bulk_create>`, so make sure it's appropriate
for your use case.
Remove in bulk
--------------
When removing objects from :class:`ManyToManyFields
<django.db.models.ManyToManyField>`, use
:meth:`~django.db.models.fields.related.RelatedManager.remove` with multiple
objects to reduce the number of SQL queries. For example::
my_band.members.remove(me, my_friend)
...is preferable to::
my_band.members.remove(me)
my_band.members.remove(my_friend)
...where ``Bands`` and ``Artists`` have a many-to-many relationship.
When removing different pairs of objects from :class:`ManyToManyFields
<django.db.models.ManyToManyField>`, use
:meth:`~django.db.models.query.QuerySet.delete` on a
:class:`~django.db.models.Q` expression with multiple
:attr:`~django.db.models.ManyToManyField.through` model instances to reduce
the number of SQL queries. For example::
from django.db.models import Q
PizzaToppingRelationship = Pizza.toppings.through
PizzaToppingRelationship.objects.filter(
Q(pizza=my_pizza, topping=pepperoni) |
Q(pizza=your_pizza, topping=pepperoni) |
Q(pizza=your_pizza, topping=mushroom)
).delete()
...is preferable to::
my_pizza.toppings.remove(pepperoni)
your_pizza.toppings.remove(pepperoni, mushroom)
...where ``Pizza`` and ``Topping`` have a many-to-many relationship.