Made sure join_field is always available in .join()

Refs #19385

django/db/models/sql/compiler.py

@@ -636,10 +636,10 @@ class SQLCompiler(object):
                         int_opts = int_model._meta
                         continue
                     lhs_col = int_opts.parents[int_model].column
+                    link_field = int_opts.get_ancestor_link(int_model)
                     int_opts = int_model._meta
                     alias = self.query.join((alias, int_opts.db_table, lhs_col,
-                            int_opts.pk.column),
-                            promote=promote)
+                            int_opts.pk.column), promote=promote, join_field=link_field)
                     alias_chain.append(alias)
             else:
                 alias = root_alias
@@ -685,10 +685,11 @@ class SQLCompiler(object):
                             int_opts = int_model._meta
                             continue
                         lhs_col = int_opts.parents[int_model].column
+                        link_field = int_opts.get_ancestor_link(int_model)
                         int_opts = int_model._meta
                         alias = self.query.join(
                             (alias, int_opts.db_table, lhs_col, int_opts.pk.column),
-                            promote=True
+                            promote=True, join_field=link_field
                         )
                         alias_chain.append(alias)
                 alias = self.query.join(

django/db/models/sql/query.py

@@ -944,6 +944,7 @@ class Query(object):
         The 'join_field' is the field we are joining along (if any).
         """
         lhs, table, lhs_col, col = connection
+        assert lhs is None or join_field is not None
         existing = self.join_map.get(connection, ())
         if reuse is None:
             reuse = existing
@@ -1003,8 +1004,9 @@ class Query(object):
         for field, model in opts.get_fields_with_model():
             if model not in seen:
                 link_field = opts.get_ancestor_link(model)
-                seen[model] = self.join((root_alias, model._meta.db_table,
-                        link_field.column, model._meta.pk.column))
+                seen[model] = self.join(
+                    (root_alias, model._meta.db_table, link_field.column,
+                     model._meta.pk.column), join_field=link_field)
         self.included_inherited_models = seen
 
     def remove_inherited_models(self):