add unique creation/deletion support to SchemaEditor.alter_field()

Author: timgraham

django_mongodb/features.py

@@ -81,12 +81,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "backends.tests.ThreadTests.test_pass_connection_between_threads",
         "backends.tests.ThreadTests.test_closing_non_shared_connections",
         "backends.tests.ThreadTests.test_default_connection_thread_local",
-        # AlterField
-        "schema.tests.SchemaTests.test_alter_field_fk_to_o2o",
-        "schema.tests.SchemaTests.test_alter_field_o2o_to_fk",
-        # AlterField (unique)
-        "schema.tests.SchemaTests.test_indexes",
-        "schema.tests.SchemaTests.test_unique",
     }
     # $bitAnd, #bitOr, and $bitXor are new in MongoDB 6.3.
     _django_test_expected_failures_bitwise = {

django_mongodb/schema.py

@@ -109,6 +109,30 @@ def _alter_field(
         strict=False,
     ):
         collection = self.connection.database[model._meta.db_table]
+        # Has unique been removed?
+        if old_field.unique and (
+            not new_field.unique or self._field_became_primary_key(old_field, new_field)
+        ):
+            # Find the unique constraint for this field
+            meta_constraint_names = {constraint.name for constraint in model._meta.constraints}
+            constraint_names = self._constraint_names(
+                model,
+                [old_field.column],
+                unique=True,
+                primary_key=False,
+                exclude=meta_constraint_names,
+            )
+            if strict and len(constraint_names) != 1:
+                raise ValueError(
+                    f"Found wrong number ({len(constraint_names)}) of unique "
+                    f"constraints for {model._meta.db_table}.{old_field.column}"
+                )
+            for constraint_name in constraint_names:
+                constraint = UniqueConstraint(
+                    fields=[old_field.name],
+                    name=constraint_name,
+                )
+                self.remove_constraint(model, constraint)
         # Removed an index? (no strict check, as multiple indexes are possible)
         # Remove indexes if db_index switched to False or a unique constraint
         # will now be used in lieu of an index. The following lines from the
@@ -134,12 +158,29 @@ def _alter_field(
             ):
                 self._drop_index_for_field(model, old_field)
                 self._add_index_for_field(model, new_field)
+            # Move unique to the new field, if needed.
+            if old_field.unique and new_field.unique and new_field.column != "_id":
+                if not old_field.primary_key:
+                    old_constraint = UniqueConstraint(
+                        fields=[old_field.name], name=f"{model._meta.db_table}_{old_field.column}_key"
+                    )
+                    self.remove_constraint(model, old_constraint)
+                new_constraint = UniqueConstraint(
+                    fields=[new_field.name], name=f"{model._meta.db_table}_{new_field.column}_key"
+                )
+                self.add_constraint(model, new_constraint, field=new_field)
         # Replace NULL with the field default if the field and was changed from
         # NULL to NOT NULL.
         if new_field.has_default() and old_field.null and not new_field.null:
             column = new_field.column
             default = self.effective_default(new_field)
             collection.update_many({column: {"$eq": None}}, [{"$set": {column: default}}])
+        # Added a unique?
+        if self._unique_should_be_added(old_field, new_field):
+            constraint = UniqueConstraint(
+                fields=[new_field.name], name=f"{model._meta.db_table}_{new_field.column}_key"
+            )
+            self.add_constraint(model, constraint, field=new_field)
         # Added an index? Add an index if db_index switched to True or a unique
         # constraint will no longer be used in lieu of an index. The following
         # lines from the truth table show all True cases; the rest are False: