- The :class:`.Query` will raise an exception when :meth:`.Query.yield_per`

is used with mappings or options where eager loading, either
joined or subquery, would take place.  These loading strategies are
not currently compatible with yield_per, so by raising this error,
the method is safer to use - combine with sending False to
:meth:`.Query.enable_eagerloads` to disable the eager loaders.

1 files changed, 35 insertions, 1 deletions

diff --git a/test/orm/test_query.py b/test/orm/test_query.py
index 984a3f93f..6ac1ba5af 100644
--- a/test/orm/test_query.py
+++ b/test/orm/test_query.py
@@ -6,7 +6,8 @@ from sqlalchemy.sql import operators, column, expression
 from sqlalchemy.engine import default
 from sqlalchemy.orm import (
     attributes, mapper, relationship, create_session, synonym, Session,
-    aliased, column_property, joinedload_all, joinedload, Query, Bundle)
+    aliased, column_property, joinedload_all, joinedload, Query, Bundle,
+    subqueryload)
 from sqlalchemy.testing.assertsql import CompiledSQL
 from sqlalchemy.testing.schema import Table, Column
 import sqlalchemy as sa
@@ -2147,6 +2148,39 @@ class YieldTest(QueryTest):
         assert q._yield_per
         eq_(q._execution_options, {"stream_results": True, "foo": "bar"})
 
+    def test_no_joinedload(self):
+        User = self.classes.User
+        sess = create_session()
+        q = sess.query(User).options(joinedload("addresses")).yield_per(1)
+        assert_raises_message(
+            sa_exc.InvalidRequestError,
+            "The yield_per Query option is currently not compatible with "
+            "joined eager loading.  Please specify ",
+            q.all
+        )
+
+    def test_no_subqueryload(self):
+        User = self.classes.User
+        sess = create_session()
+        q = sess.query(User).options(subqueryload("addresses")).yield_per(1)
+        assert_raises_message(
+            sa_exc.InvalidRequestError,
+            "The yield_per Query option is currently not compatible with "
+            "subquery eager loading.  Please specify ",
+            q.all
+        )
+
+    def test_eagerload_disable(self):
+        User = self.classes.User
+        sess = create_session()
+        q = sess.query(User).options(subqueryload("addresses")).\
+            enable_eagerloads(False).yield_per(1)
+        q.all()
+
+        q = sess.query(User).options(joinedload("addresses")).\
+            enable_eagerloads(False).yield_per(1)
+        q.all()
+
 
 class HintsTest(QueryTest, AssertsCompiledSQL):
     def test_hints(self):