Fix non empty initial query.

Author: WaVEV

django_mongodb/compiler.py

@@ -441,7 +441,11 @@ def project_field(column):
 
     @cached_property
     def collection_name(self):
-        base_table = next(v for v in self.query.alias_map.values() if isinstance(v, BaseTable))
+        base_table = next(
+            v
+            for k, v in self.query.alias_map.items()
+            if isinstance(v, BaseTable) and self.query.alias_refcount[k]
+        )
         return base_table.table_alias or base_table.table_name
 
     @cached_property

django_mongodb/expressions.py

@@ -95,13 +95,13 @@ def query(self, compiler, connection):
     subquery_compiler.parent_collections = {compiler.collection_name} | compiler.parent_collections
     columns = subquery_compiler.get_columns()
     field_name, expr = columns[0]
+    result_query = subquery_compiler.query_class(subquery_compiler)
     subquery = subquery_compiler.build_query(
         columns
         if subquery_compiler.query.annotations or not subquery_compiler.query.default_cols
         else None
     )
     table_output = f"__subquery{len(compiler.subqueries)}"
-    result_query = compiler.query_class(compiler)
     pipeline = subquery.get_pipeline()
     # the result must be a list of values. Se we compress the output
     if not self.has_limit_one():