fix ManyToManyField repointing

Author: timgraham

django_mongodb/features.py

@@ -122,11 +122,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         # alter_unique_together
         "schema.tests.SchemaTests.test_remove_unique_together_does_not_remove_meta_constraints",
         "schema.tests.SchemaTests.test_unique_together",
-        # ManyToManyField
-        "schema.tests.SchemaTests.test_m2m_repoint",
-        "schema.tests.SchemaTests.test_m2m_repoint_custom",
-        "schema.tests.SchemaTests.test_m2m_repoint_inherited",
-        "schema.tests.SchemaTests.test_m2m_through_remove",
         # add/remove_constraint
         "schema.tests.SchemaTests.test_composed_constraint_with_fk",
         "schema.tests.SchemaTests.test_remove_ignored_unique_constraint_not_create_fk_index",

django_mongodb/fields/auto.py

@@ -1,6 +1,6 @@
 from bson import ObjectId, errors
 from django.core import exceptions
-from django.db.models.fields import AutoField, Field
+from django.db.models.fields import AutoField
 from django.utils.functional import cached_property
 from django.utils.translation import gettext_lazy as _
 
@@ -31,8 +31,8 @@ def get_prep_value(self, value):
                 return int(value)
             raise ValueError(f"Field '{self.name}' expected an ObjectId but got {value!r}.") from e
 
-    def rel_db_type(self, connection):
-        return Field().db_type(connection=connection)
+    def db_type(self, connection):
+        return "ObjectId"
 
     def to_python(self, value):
         if value is None or isinstance(value, int):

django_mongodb/schema.py

@@ -27,7 +27,17 @@ def add_field(self, model, field):
                 {}, [{"$set": {column: self.effective_default(field)}}]
             )
 
-    def alter_field(self, model, old_field, new_field, strict=False):
+    def _alter_field(
+        self,
+        model,
+        old_field,
+        new_field,
+        old_type,
+        new_type,
+        old_db_params,
+        new_db_params,
+        strict=False,
+    ):
         pass
 
     def remove_field(self, model, field):