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

Author: timgraham

django_mongodb/features.py

@@ -79,16 +79,12 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         # AddField
         "schema.tests.SchemaTests.test_add_unique_charfield",
         # AlterField
-        "schema.tests.SchemaTests.test_alter_field_add_index_to_integerfield",
         "schema.tests.SchemaTests.test_alter_field_fk_to_o2o",
         "schema.tests.SchemaTests.test_alter_field_o2o_keeps_unique",
         "schema.tests.SchemaTests.test_alter_field_o2o_to_fk",
         "schema.tests.SchemaTests.test_alter_int_pk_to_int_unique",
-        # AlterField (db_index)
-        "schema.tests.SchemaTests.test_alter_renames_index",
-        "schema.tests.SchemaTests.test_indexes",
-        "schema.tests.SchemaTests.test_remove_db_index_doesnt_remove_custom_indexes",
         # AlterField (unique)
+        "schema.tests.SchemaTests.test_indexes",
         "schema.tests.SchemaTests.test_unique",
         "schema.tests.SchemaTests.test_unique_and_reverse_m2m",
         # alter_unique_together

django_mongodb/schema.py

@@ -66,15 +66,52 @@ def _alter_field(
         strict=False,
     ):
         collection = self.connection.database[model._meta.db_table]
+        # 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
+        # truth table show all True cases; the rest are False:
+        #
+        # old_field.db_index | old_field.unique | new_field.db_index | new_field.unique
+        # ------------------------------------------------------------------------------
+        # True               | False            | False              | False
+        # True               | False            | False              | True
+        # True               | False            | True               | True
+        if (
+            old_field.db_index
+            and not old_field.unique
+            and (not new_field.db_index or new_field.unique)
+        ):
+            self._remove_field_index(model, old_field)
         # Have they renamed the column?
         if old_field.column != new_field.column:
             collection.update_many({}, {"$rename": {old_field.column: new_field.column}})
+            # Move index to the new field, if needed.
+            if self._field_should_be_indexed(model, old_field) and self._field_should_be_indexed(
+                model, new_field
+            ):
+                self._remove_field_index(model, old_field)
+                self._add_field_index(model, new_field)
         # Replace NULL with the field default if the field and was changed from
         # NULL to NOT NULL.
         if new_field.has_default() and old_field.null and not new_field.null:
             column = new_field.column
             default = self.effective_default(new_field)
             collection.update_many({column: {"$eq": None}}, [{"$set": {column: default}}])
+        # Added 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:
+        #
+        # old_field.db_index | old_field.unique | new_field.db_index | new_field.unique
+        # ------------------------------------------------------------------------------
+        # False              | False            | True               | False
+        # False              | True             | True               | False
+        # True               | True             | True               | False
+        if (
+            (not old_field.db_index or old_field.unique)
+            and new_field.db_index
+            and not new_field.unique
+        ):
+            self._add_field_index(model, new_field)
 
     def remove_field(self, model, field):
         # Remove implicit M2M tables.
@@ -152,6 +189,27 @@ def _remove_composed_index(self, model, field_names, constraint_kwargs):
         collection = self.connection.database[model._meta.db_table]
         collection.drop_index(constraint_names[0])
 
+    def _remove_field_index(self, model, field):
+        collection = self.connection.database[model._meta.db_table]
+        # Find the index for this field
+        meta_index_names = {index.name for index in model._meta.indexes}
+        # Retrieve only BTREE indexes since this is what's created with
+        # db_index=True.
+        index_names = self._constraint_names(
+            model,
+            [field.column],
+            index=True,
+            type_=Index.suffix,
+            exclude=meta_index_names,
+        )
+        if not index_names:
+            raise ValueError(f"Index not found for {model._meta.db_table}.{field.column}.")
+        for index_name in index_names:
+            # The only way to check if an index was created with
+            # db_index=True or with Index(['field'], name='foo')
+            # is to look at its name (refs #28053).
+            collection.drop_index(index_name)
+
     def add_constraint(self, model, constraint):
         pass