Fixed #24591 -- Optimized cloning of ModelState objects. (1a1f16d6) · Commits · Dom Sekotill / django

django/db/migrations/state.py

+14 −3

Original line number	Diff line number	Diff line
		@@ -312,12 +312,23 @@ class ModelState(object):
		# Sanity-check that fields is NOT a dict. It must be ordered.
		if isinstance(self.fields, dict):
		raise ValueError("ModelState.fields cannot be a dict - it must be a list of 2-tuples.")
		# Sanity-check that fields are NOT already bound to a model.
		for name, field in fields:
		# Sanity-check that fields are NOT already bound to a model.
		if hasattr(field, 'model'):
		raise ValueError(
		'ModelState.fields cannot be bound to a model - "%s" is.' % name
		)
		# Sanity-check that relation fields are NOT referring to a model class.
		if field.is_relation and hasattr(field.related_model, '_meta'):
		raise ValueError(
		'ModelState.fields cannot refer to a model class - "%s.to" does. '
		'Use a string reference instead.' % name
		)
		if field.many_to_many and hasattr(field.remote_field.through, '_meta'):
		raise ValueError(
		'ModelState.fields cannot refer to a model class - "%s.through" does. '
		'Use a string reference instead.' % name
		)

		@cached_property
		def name_lower(self):
		@@ -502,10 +513,10 @@ class ModelState(object):
		return self.__class__(
		app_label=self.app_label,
		name=self.name,
		fields=list(self.construct_fields()),
		fields=list(self.fields),
		options=dict(self.options),
		bases=self.bases,
		managers=list(self.construct_managers()),
		managers=list(self.managers),
		)

		def render(self, apps):

+12 −1

Original line number	Diff line number	Diff line
		@@ -402,7 +402,8 @@ You can take this template and work from it, though we suggest looking at the
		built-in Django operations in ``django.db.migrations.operations`` - they're
		easy to read and cover a lot of the example usage of semi-internal aspects
		of the migration framework like ``ProjectState`` and the patterns used to get
		historical models.
		historical models, as well as ``ModelState`` and the patterns used to mutate
		historical models in ``state_forwards()``.

		Some things to note:

		@@ -421,6 +422,16 @@ Some things to note:
		operations; this is part of the autodetection code and does not matter for
		custom operations.

		.. warning::

		For performance reasons, the :class:`~django.db.models.Field` instances in
		``ModelState.fields`` are reused across migrations. You must never change
		the attributes on these instances. If you need to mutate a field in
		``state_forwards()``, you must remove the old instance from
		``ModelState.fields`` and add a new instance in its place. The same is true
		for the :class:`~django.db.models.Manager` instances in
		``ModelState.managers``.

		As a simple example, let's make an operation that loads PostgreSQL extensions
		(which contain some of PostgreSQL's more exciting features). It's simple enough;
		there's no model state changes, and all it does is run one command::

+16 −0

Original line number	Diff line number	Diff line
		@@ -10,6 +10,7 @@ from django.test import SimpleTestCase, TestCase, override_settings

		from .models import (
		FoodManager, FoodQuerySet, ModelWithCustomBase, NoMigrationFoodManager,
		UnicodeModel,
		)


		@@ -695,6 +696,21 @@ class ModelStateTests(TestCase):
		'ModelState.fields cannot be bound to a model - "field" is.'):
		ModelState('app', 'Model', [('field', field)])

		def test_sanity_check_to(self):
		field = models.ForeignKey(UnicodeModel)
		with self.assertRaisesMessage(ValueError,
		'ModelState.fields cannot refer to a model class - "field.to" does. '
		'Use a string reference instead.'):
		ModelState('app', 'Model', [('field', field)])

		def test_sanity_check_through(self):
		field = models.ManyToManyField('UnicodeModel')
		field.remote_field.through = UnicodeModel
		with self.assertRaisesMessage(ValueError,
		'ModelState.fields cannot refer to a model class - "field.through" does. '
		'Use a string reference instead.'):
		ModelState('app', 'Model', [('field', field)])

		def test_fields_immutability(self):
		"""
		Tests that rendering a model state doesn't alter its internal fields.