add support for partial indexes

Author: WaVEV

django_mongodb/__init__.py

@@ -10,12 +10,14 @@
 from .expressions import register_expressions  # noqa: E402
 from .fields import register_fields  # noqa: E402
 from .functions import register_functions  # noqa: E402
+from .indexes import register_indexes  # noqa: E402
 from .lookups import register_lookups  # noqa: E402
 from .query import register_nodes  # noqa: E402
 
 register_aggregates()
 register_expressions()
 register_fields()
 register_functions()
+register_indexes()
 register_lookups()
 register_nodes()

django_mongodb/expressions.py

@@ -64,7 +64,8 @@ def col(self, compiler, connection):  # noqa: ARG001
             compiler.column_indices[self] = index
         return f"$${compiler.PARENT_FIELD_TEMPLATE.format(index)}"
     # Add the column's collection's alias for columns in joined collections.
-    prefix = f"{self.alias}." if self.alias != compiler.collection_name else ""
+    has_alias = self.alias and self.alias != compiler.collection_name
+    prefix = f"{self.alias}." if has_alias else ""
     return f"${prefix}{self.target.column}"
 
 

django_mongodb/features.py

@@ -25,8 +25,6 @@ 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
@@ -59,6 +57,11 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "db_functions.datetime.test_extract_trunc.DateFunctionWithTimeZoneTests.test_trunc_timezone_applied_before_truncation",
         # Length of null considered zero rather than null.
         "db_functions.text.test_length.LengthTests.test_basic",
+        # Partial indexes don't support multiple conditions. It requires this
+        # backend to convert $aggregate MQL syntax to $find (or else just
+        # generate $find syntax in the first place).
+        "indexes.tests.PartialIndexTests.test_is_null_condition",
+        "indexes.tests.PartialIndexTests.test_multiple_conditions",
         # Unexpected alias_refcount in alias_map.
         "queries.tests.Queries1Tests.test_order_by_tables",
         # The $sum aggregation returns 0 instead of None for null.
@@ -96,11 +99,17 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "expressions.tests.ExpressionOperatorTests.test_lefthand_bitwise_xor_right_null",
         "expressions.tests.ExpressionOperatorTests.test_lefthand_transformed_field_bitwise_or",
     }
+    # Before MongoDB 6.0, $in cannot be used in partialFilterExpression.
+    _django_test_expected_failures_partial_expression_in = {
+        "schema.tests.SchemaTests.test_remove_ignored_unique_constraint_not_create_fk_index",
+    }
 
     @cached_property
     def django_test_expected_failures(self):
         expected_failures = super().django_test_expected_failures
         expected_failures.update(self._django_test_expected_failures)
+        if not self.is_mongodb_6_0:
+            expected_failures.update(self._django_test_expected_failures_partial_expression_in)
         if not self.is_mongodb_6_3:
             expected_failures.update(self._django_test_expected_failures_bitwise)
         return expected_failures
@@ -602,6 +611,10 @@ def django_test_expected_failures(self):
         },
     }
 
+    @cached_property
+    def is_mongodb_6_0(self):
+        return self.connection.get_database_version() >= (6, 0)
+
     @cached_property
     def is_mongodb_6_3(self):
         return self.connection.get_database_version() >= (6, 3)

django_mongodb/indexes.py

@@ -0,0 +1,23 @@
+from django.db.models import Index
+from django.db.models.sql.query import Query
+
+
+def _get_condition_mql(self, model, schema_editor):
+    """Analogous to Index._get_condition_sql()."""
+    query = Query(model=model, alias_cols=False)
+    where = query.build_where(self.condition)
+    compiler = query.get_compiler(connection=schema_editor.connection)
+    mql_ = where.as_mql(compiler, schema_editor.connection)
+    # Transform aggregate() query syntax into find() syntax.
+    mql = {}
+    for key in mql_:
+        col, value = mql_[key]
+        # multiple conditions don't work yet
+        if isinstance(col, dict):
+            return {}
+        mql[col.lstrip("$")] = {key: value}
+    return mql
+
+
+def register_indexes():
+    Index._get_condition_mql = _get_condition_mql

django_mongodb/schema.py

@@ -1,3 +1,5 @@
+from collections import defaultdict
+
 from django.db.backends.base.schema import BaseDatabaseSchemaEditor
 from django.db.models import Index, UniqueConstraint
 from pymongo import ASCENDING, DESCENDING
@@ -166,17 +168,23 @@ def add_index(self, model, index, field=None, unique=False):
         if index.contains_expressions:
             return
         kwargs = {}
+        filter_expression = defaultdict(dict)
+        if index.condition:
+            filter_expression.update(index._get_condition_mql(model, self))
         if unique:
-            filter_expression = {}
+            kwargs["unique"] = True
             # 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)}
+                filter_expression[field.column].update({"$type": field.db_type(self.connection)})
             else:
                 for field_name, _ in index.fields_orders:
                     field_ = model._meta.get_field(field_name)
-                    filter_expression[field_.column] = {"$type": field_.db_type(self.connection)}
-            kwargs = {"partialFilterExpression": filter_expression, "unique": True}
+                    filter_expression[field_.column].update(
+                        {"$type": field_.db_type(self.connection)}
+                    )
+        if filter_expression:
+            kwargs["partialFilterExpression"] = filter_expression
         index_orders = (
             [(field.column, ASCENDING)]
             if field
@@ -260,7 +268,11 @@ def add_constraint(self, model, constraint, field=None):
             expressions=constraint.expressions,
             nulls_distinct=constraint.nulls_distinct,
         ):
-            idx = Index(fields=constraint.fields, name=constraint.name)
+            idx = Index(
+                fields=constraint.fields,
+                name=constraint.name,
+                condition=constraint.condition,
+            )
             self.add_index(model, idx, field=field, unique=True)
 
     def _add_field_unique(self, model, field):
@@ -276,7 +288,11 @@ def remove_constraint(self, model, constraint):
             expressions=constraint.expressions,
             nulls_distinct=constraint.nulls_distinct,
         ):
-            idx = Index(fields=constraint.fields, name=constraint.name)
+            idx = Index(
+                fields=constraint.fields,
+                name=constraint.name,
+                condition=constraint.condition,
+            )
             self.remove_index(model, idx)
 
     def _remove_field_unique(self, model, field):