Commit a9e29fae authored by Markus Holtermann's avatar Markus Holtermann
Browse files

Fixed #24435 -- Prevented m2m field removal and addition in migrations when changing blank 

Thanks Mark Tranchant for the report an Tim Graham for the test and
review.
parent 70123cf0

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