edits.

Author: WaVEV

django_mongodb_backend/expressions/builtins.py

@@ -25,7 +25,6 @@
     Value,
     When,
 )
-from django.db.models.indexes import IndexExpression
 from django.db.models.sql import Query
 
 from django_mongodb_backend.query_utils import process_lhs
@@ -107,19 +106,6 @@ def expression_wrapper(self, compiler, connection):
     return self.expression.as_mql(compiler, connection, as_expr=True)
 
 
-def index_expression(self, compiler, connection, as_expr=False):  # noqa: ARG001
-    result = []
-    for expr in self.get_source_expressions():
-        if expr is None:
-            continue
-        for sub_expr in expr.get_source_expressions():
-            try:
-                result.append(sub_expr.as_mql(compiler, connection))
-            except FullResultSet:
-                result.append(Value(True).as_mql(compiler, connection))
-    return result
-
-
 def negated_expression(self, compiler, connection):
     return {"$not": expression_wrapper(self, compiler, connection)}
 
@@ -258,7 +244,6 @@ def register_expressions():
     Exists.as_mql_expr = exists
     ExpressionList.as_mql = process_lhs
     ExpressionWrapper.as_mql_expr = expression_wrapper
-    IndexExpression.as_mql = index_expression
     NegatedExpression.as_mql_expr = negated_expression
     OrderBy.as_mql_expr = partialmethod(order_by, as_expr=True)
     OrderBy.as_mql_path = partialmethod(order_by, as_expr=False)

django_mongodb_backend/indexes.py

@@ -5,13 +5,15 @@
 from django.db import NotSupportedError
 from django.db.models import FloatField, Index, IntegerField
 from django.db.models.expressions import OrderBy
+from django.db.models.indexes import IndexExpression
 from django.db.models.lookups import BuiltinLookup
 from django.db.models.sql.query import Query
 from django.db.models.sql.where import AND, XOR, WhereNode
 from pymongo import ASCENDING, DESCENDING
 from pymongo.operations import IndexModel, SearchIndexModel
 
 from django_mongodb_backend.fields import ArrayField
+from django_mongodb_backend.query_utils import process_lhs
 
 from .query_utils import process_rhs
 
@@ -342,4 +344,5 @@ def register_indexes():
     BuiltinLookup.as_mql_idx = builtin_lookup_idx
     Index._get_condition_mql = _get_condition_mql
     Index.get_pymongo_index_model = get_pymongo_index_model
+    IndexExpression.as_mql = process_lhs
     WhereNode.as_mql_idx = where_node_idx

django_mongodb_backend/schema.py

@@ -353,6 +353,7 @@ def _remove_field_index(self, model, field, column_prefix=""):
         collection.drop_index(index_names[0])
 
     def _check_expression_indexes_applicable(self, expressions):
+        # Check if all expressions are field references or ORDER BY expressions on a field.
         return all(
             isinstance(expression.expression if isinstance(expression, OrderBy) else expression, F)
             for expression in expressions
@@ -373,6 +374,7 @@ def _unique_supported(
             and (
                 not expressions
                 or self.connection.features.supports_expression_indexes
+                # Expression indexes are partially supported.
                 or self._check_expression_indexes_applicable(expressions)
             )
             and (