Refactor base_table and collection_name.

django_mongodb/compiler.py

@@ -436,23 +436,24 @@ def project_field(column):
     @cached_property
     def base_table(self):
         return next(
-            v
-            for k, v in self.query.alias_map.items()
-            if isinstance(v, BaseTable) and self.query.alias_refcount[k]
+            (
+                v
+                for k, v in self.query.alias_map.items()
+                if isinstance(v, BaseTable) and self.query.alias_refcount[k]
+            ),
+            None,
         )
 
     @cached_property
     def collection_name(self):
-        try:
-            base_table = self.base_table
-        except StopIteration:
-            # Use a dummy collection if the query doesn't specify a table
-            # (such as Constraint.validate() with a condition).
-            query = self.query_class(self)
-            query.aggregation_pipeline = [{"$facet": {"__null": []}}]
-            self.subqueries.insert(0, query)
-            return "__null"
-        return base_table.table_alias or base_table.table_name
+        if self.base_table:
+            return self.base_table.table_alias or self.base_table.table_name
+        # Use a dummy collection if the query doesn't specify a table
+        # (such as Constraint.validate() with a condition).
+        query = self.query_class(self)
+        query.aggregation_pipeline = [{"$facet": {"__null": []}}]
+        self.subqueries.insert(0, query)
+        return "__null"
 
     @cached_property
     def collection(self):