refactor: set cascade_backrefs=False for SavedQuery

pytest.ini

@@ -30,7 +30,7 @@ filterwarnings =
     always::sqlalchemy.exc.RemovedIn20Warning
     error:Passing a string to Connection.execute\(\) is deprecated:sqlalchemy.exc.RemovedIn20Warning
     error:"Query" object is being merged into a Session:sqlalchemy.exc.RemovedIn20Warning
-#    error:"SavedQuery" object is being merged into a Session:sqlalchemy.exc.RemovedIn20Warning
+    error:"SavedQuery" object is being merged into a Session:sqlalchemy.exc.RemovedIn20Warning
     error:"SqlaTable" object is being merged into a Session:sqlalchemy.exc.RemovedIn20Warning
 #    error:"SqlMetric" object is being merged into a Session:sqlalchemy.exc.RemovedIn20Warning
 #    error:"TableColumn" object is being merged into a Session:sqlalchemy.exc.RemovedIn20Warning

superset/models/sql_lab.py

@@ -500,13 +500,25 @@ class SavedQuery(
     template_parameters = Column(Text)
     user = relationship(
         security_manager.user_model,
-        backref=backref("saved_queries", cascade="all, delete-orphan"),
+        backref=backref(
+            "saved_queries",
+            cascade="all, delete-orphan",
+            # SQLAlchemy 2.0 behavior: assigning `saved_query.user` no longer
+            # cascades the SavedQuery into the User's session; callers must
+            # add objects to a session explicitly.
+            cascade_backrefs=False,
+        ),
         foreign_keys=[user_id],
     )
     database = relationship(
         "Database",
         foreign_keys=[db_id],
-        backref=backref("saved_queries", cascade="all, delete-orphan"),
+        backref=backref(
+            "saved_queries",
+            cascade="all, delete-orphan",
+            # SQLAlchemy 2.0 behavior: see `user` above.
+            cascade_backrefs=False,
+        ),
     )
     rows = Column(Integer, nullable=True)
     last_run = Column(DateTime, nullable=True)