Commit bff446c2 authored by Markus Holtermann's avatar Markus Holtermann
Browse files

[1.8.x] Fixed #24435 -- Prevented m2m field removal and addition in migrations when changing blank 

Thanks Mark Tranchant for the report and Tim Graham for the test and
review.

Backport of a9e29fae from master
parent 44dd65fb

django/db/migrations/autodetector.py

+11 −2
Original line number Diff line number Diff line
@@ -848,8 +848,16 @@ class MigrationAutodetector(object): 
            old_field_dec = self.deep_deconstruct(old_field)

            new_field_dec = self.deep_deconstruct(new_field)

            if old_field_dec != new_field_dec:

                if (not isinstance(old_field, models.ManyToManyField) and

                        not isinstance(new_field, models.ManyToManyField)):

                both_m2m = (

                    isinstance(old_field, models.ManyToManyField) and

                    isinstance(new_field, models.ManyToManyField)

                )

                neither_m2m = (

                    not isinstance(old_field, models.ManyToManyField) and

                    not isinstance(new_field, models.ManyToManyField)

                )

                if both_m2m or neither_m2m:

                    # Either both fields are m2m or neither is

                    preserve_default = True

                    if (old_field.null and not new_field.null and not new_field.has_default() and

                            not isinstance(new_field, models.ManyToManyField)):
@@ -870,6 +878,7 @@ class MigrationAutodetector(object): 
                        )

                    )

                else:

                    # We cannot alter between m2m and concrete fields

                    self._generate_removed_field(app_label, model_name, field_name)

                    self._generate_added_field(app_label, model_name, field_name)

tests/migrations/test_autodetector.py

+14 −0
Original line number Diff line number Diff line
@@ -127,6 +127,10 @@ class AutodetectorTests(TestCase): 
        ("id", models.AutoField(primary_key=True)),

        ("publishers", models.ManyToManyField("testapp.Publisher")),

    ])

    author_with_m2m_blank = ModelState("testapp", "Author", [

        ("id", models.AutoField(primary_key=True)),

        ("publishers", models.ManyToManyField("testapp.Publisher", blank=True)),

    ])

    author_with_m2m_through = ModelState("testapp", "Author", [

        ("id", models.AutoField(primary_key=True)),

        ("publishers", models.ManyToManyField("testapp.Publisher", through="testapp.Contract")),
@@ -1263,6 +1267,16 @@ class AutodetectorTests(TestCase): 
        self.assertOperationTypes(changes, 'testapp', 0, ["AddField"])

        self.assertOperationAttributes(changes, 'testapp', 0, 0, name="publishers")



    def test_alter_many_to_many(self):

        before = self.make_project_state([self.author_with_m2m, self.publisher])

        after = self.make_project_state([self.author_with_m2m_blank, self.publisher])

        autodetector = MigrationAutodetector(before, after)

        changes = autodetector._detect_changes()

        # Right number/type of migrations?

        self.assertNumberMigrations(changes, 'testapp', 1)

        self.assertOperationTypes(changes, 'testapp', 0, ["AlterField"])

        self.assertOperationAttributes(changes, 'testapp', 0, 0, name="publishers")



    def test_create_with_through_model(self):

        """

        Adding a m2m with a through model and the models that use it should be