implement SchemaEditor.add/remove_constraint()

And also creating uniques in create_model() and add_field(),
and removing them in remove_field().

Author: timgraham

django_mongodb/features.py

@@ -14,6 +14,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_collation_on_charfield = False
     supports_column_check_constraints = False
     supports_date_lookup_using_string = False
+    supports_deferrable_unique_constraints = False
     supports_explaining_query_execution = True
     supports_expression_defaults = False
     supports_expression_indexes = False
@@ -23,6 +24,8 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     # BSON Date type doesn't support microsecond precision.
     supports_microsecond_precision = False
     supports_paramstyle_pyformat = False
+    # Not implemented.
+    supports_partial_indexes = False
     supports_select_difference = False
     supports_select_intersection = False
     supports_sequence_reset = False
@@ -70,28 +73,15 @@ 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",
-        # AddField
-        "schema.tests.SchemaTests.test_add_unique_charfield",
         # AlterField
         "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 (unique)
         "schema.tests.SchemaTests.test_indexes",
         "schema.tests.SchemaTests.test_unique",
-        "schema.tests.SchemaTests.test_unique_and_reverse_m2m",
         # alter_unique_together
         "migrations.test_operations.OperationTests.test_alter_unique_together",
         "schema.tests.SchemaTests.test_unique_together",
-        # add/remove_constraint
-        "introspection.tests.IntrospectionTests.test_get_constraints",
-        "migrations.test_operations.OperationTests.test_add_partial_unique_constraint",
-        "migrations.test_operations.OperationTests.test_create_model_with_partial_unique_constraint",
-        "migrations.test_operations.OperationTests.test_remove_partial_unique_constraint",
-        "schema.tests.SchemaTests.test_composed_constraint_with_fk",
-        "schema.tests.SchemaTests.test_remove_ignored_unique_constraint_not_create_fk_index",
-        "schema.tests.SchemaTests.test_unique_constraint",
         # Column default values aren't handled when a field raises
         # EmptyResultSet: https://github.com/mongodb-labs/django-mongodb/issues/155
         "annotations.tests.NonAggregateAnnotationTestCase.test_empty_queryset_annotation",
@@ -195,24 +185,6 @@ def django_test_expected_failures(self):
             "model_fields.test_autofield.SmallAutoFieldTests",
             "queries.tests.TestInvalidValuesRelation.test_invalid_values",
         },
-        "MongoDB does not enforce UNIQUE constraints.": {
-            "auth_tests.test_basic.BasicTestCase.test_unicode_username",
-            "auth_tests.test_migrations.ProxyModelWithSameAppLabelTests.test_migrate_with_existing_target_permission",
-            "constraints.tests.UniqueConstraintTests.test_database_constraint",
-            "contenttypes_tests.test_operations.ContentTypeOperationsTests.test_content_type_rename_conflict",
-            "contenttypes_tests.test_operations.ContentTypeOperationsTests.test_existing_content_type_rename",
-            "custom_pk.tests.CustomPKTests.test_unique_pk",
-            "force_insert_update.tests.ForceInsertInheritanceTests.test_force_insert_with_existing_grandparent",
-            "get_or_create.tests.GetOrCreateTestsWithManualPKs.test_create_with_duplicate_primary_key",
-            "get_or_create.tests.GetOrCreateTestsWithManualPKs.test_savepoint_rollback",
-            "get_or_create.tests.GetOrCreateThroughManyToMany.test_something",
-            "get_or_create.tests.UpdateOrCreateTests.test_manual_primary_key_test",
-            "get_or_create.tests.UpdateOrCreateTestsWithManualPKs.test_create_with_duplicate_primary_key",
-            "introspection.tests.IntrospectionTests.test_get_constraints_unique_indexes_orders",
-            "model_fields.test_filefield.FileFieldTests.test_unique_when_same_filename",
-            "one_to_one.tests.OneToOneTests.test_multiple_o2o",
-            "queries.test_bulk_update.BulkUpdateTests.test_database_routing_batch_atomicity",
-        },
         "MongoDB does not enforce PositiveIntegerField constraint.": {
             "model_fields.test_integerfield.PositiveIntegerFieldTests.test_negative_values",
         },

django_mongodb/schema.py

@@ -1,5 +1,5 @@
 from django.db.backends.base.schema import BaseDatabaseSchemaEditor
-from django.db.models import Index
+from django.db.models import Index, UniqueConstraint
 from pymongo import ASCENDING, DESCENDING
 from pymongo.operations import IndexModel
 
@@ -29,18 +29,23 @@ def create_model(self, model):
 
     def _create_model_indexes(self, model):
         """
-        Create all indexes (field indexes, index_together, Meta.indexes) for
-        the specified model.
+        Create all indexes (field indexes & uniques, Meta.index_together,
+        Meta.constraints, Meta.indexes) for the specified model.
         """
         if not model._meta.managed or model._meta.proxy or model._meta.swapped:
             return
-        # Field indexes
+        # Field indexes and uniques
         for field in model._meta.local_fields:
             if self._field_should_be_indexed(model, field):
                 self._add_field_index(model, field)
+            elif self._field_should_have_unique(field):
+                self._add_field_unique(model, field)
         # Meta.index_together (RemovedInDjango51Warning)
         for field_names in model._meta.index_together:
             self._add_composed_index(model, field_names)
+        # Meta.constraints
+        for constraint in model._meta.constraints:
+            self.add_constraint(model, constraint)
         # Meta.indexes
         for index in model._meta.indexes:
             self.add_index(model, index)
@@ -62,9 +67,11 @@ def add_field(self, model, field):
             self.get_collection(model._meta.db_table).update_many(
                 {}, [{"$set": {column: self.effective_default(field)}}]
             )
-        # Add an index, if required.
+        # Add an index or unique, if required.
         if self._field_should_be_indexed(model, field):
             self._add_field_index(model, field)
+        elif self._field_should_have_unique(field):
+            self._add_field_unique(model, field)
 
     def _alter_field(
         self,
@@ -110,6 +117,8 @@ def remove_field(self, model, field):
             self.get_collection(model._meta.db_table).update_many({}, {"$unset": {column: ""}})
             if self._field_should_be_indexed(model, field):
                 self._remove_field_index(model, field)
+            elif self._field_should_have_unique(field):
+                self._remove_field_unique(model, field)
 
     def alter_index_together(self, model, old_index_together, new_index_together):
         olds = {tuple(fields) for fields in old_index_together}
@@ -124,9 +133,21 @@ def alter_index_together(self, model, old_index_together, new_index_together):
     def alter_unique_together(self, model, old_unique_together, new_unique_together):
         pass
 
-    def add_index(self, model, index, field=None):
+    def add_index(self, model, index, field=None, unique=False):
         if index.contains_expressions:
             return
+        kwargs = {}
+        if unique:
+            filter_expression = {}
+            # Indexing on $type matches the value of most SQL databases by
+            # allowing multiple null values for the unique constraint.
+            if field:
+                filter_expression[field.column] = {"$type": field.db_type(self.connection)}
+            else:
+                for field_name, _ in index.fields_orders:
+                    field_ = model._meta.get_field(field_name)
+                    filter_expression[field_.column] = {"$type": field_.db_type(self.connection)}
+            kwargs = {"partialFilterExpression": filter_expression, "unique": True}
         index_orders = (
             [(field.column, ASCENDING)]
             if field
@@ -137,7 +158,7 @@ def add_index(self, model, index, field=None):
                 for field_name, order in index.fields_orders
             ]
         )
-        idx = IndexModel(index_orders, name=index.name)
+        idx = IndexModel(index_orders, name=index.name, **kwargs)
         self.get_collection(model._meta.db_table).create_indexes([idx])
 
     def _add_composed_index(self, model, field_names):
@@ -202,13 +223,57 @@ def _remove_field_index(self, model, field):
             )
         collection.drop_index(index_names[0])
 
-    def add_constraint(self, model, constraint):
-        pass
+    def add_constraint(self, model, constraint, field=None):
+        if isinstance(constraint, UniqueConstraint) and self._unique_supported(
+            condition=constraint.condition,
+            deferrable=constraint.deferrable,
+            include=constraint.include,
+            expressions=constraint.expressions,
+            nulls_distinct=constraint.nulls_distinct,
+        ):
+            idx = Index(fields=constraint.fields, name=constraint.name)
+            self.add_index(model, idx, field=field, unique=True)
+
+    def _add_field_unique(self, model, field):
+        name = str(self._unique_constraint_name(model._meta.db_table, [field.column]))
+        constraint = UniqueConstraint(fields=[field.name], name=name)
+        self.add_constraint(model, constraint, field=field)
 
     def remove_constraint(self, model, constraint):
-        pass
+        if isinstance(constraint, UniqueConstraint) and self._unique_supported(
+            condition=constraint.condition,
+            deferrable=constraint.deferrable,
+            include=constraint.include,
+            expressions=constraint.expressions,
+            nulls_distinct=constraint.nulls_distinct,
+        ):
+            idx = Index(fields=constraint.fields, name=constraint.name)
+            self.remove_index(model, idx)
+
+    def _remove_field_unique(self, model, 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,
+            [field.column],
+            unique=True,
+            primary_key=False,
+            exclude=meta_constraint_names,
+        )
+        if len(constraint_names) != 1:
+            num_found = len(constraint_names)
+            raise ValueError(
+                f"Found wrong number ({num_found}) of unique constraints for "
+                f"{model._meta.db_table}.{field.column}."
+            )
+        self.get_collection(model._meta.db_table).drop_index(constraint_names[0])
 
     def alter_db_table(self, model, old_db_table, new_db_table):
         if old_db_table == new_db_table:
             return
         self.get_collection(old_db_table).rename(new_db_table)
+
+    def _field_should_have_unique(self, field):
+        db_type = field.db_type(self.connection)
+        # The _id column is automatically unique.
+        return db_type and field.unique and field.column != "_id"