Merge "Improve error message when using :meth:`_query.Query.filter_by` in a query where the first entity is not a mapped class."

1 files changed, 10 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index 02cfbfcb2..7e65f26e2 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -1784,8 +1784,17 @@ class Query(Generative):
 
         """
 
+        zero = self._joinpoint_zero()
+        if zero is None:
+            raise sa_exc.InvalidRequestError(
+                "Can't use filter_by when the first entity '%s' of a query "
+                "is not a mapped class. Please use the filter method instead, "
+                "or change the order of the entities in the query"
+                % self._query_entity_zero()
+            )
+
         clauses = [
-            _entity_descriptor(self._joinpoint_zero(), key) == value
+            _entity_descriptor(zero, key) == value
             for key, value in kwargs.items()
         ]
         return self.filter(*clauses)