Merge "Detect back_populates referring to non-relationship"

2 files changed, 41 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/relationships.py b/lib/sqlalchemy/orm/relationships.py
index 5d87ef797..00a14b04c 100644
--- a/lib/sqlalchemy/orm/relationships.py
+++ b/lib/sqlalchemy/orm/relationships.py
@@ -2046,6 +2046,13 @@ class RelationshipProperty(StrategizedProperty):
 
     def _add_reverse_property(self, key):
         other = self.mapper.get_property(key, _configure_mappers=False)
+        if not isinstance(other, RelationshipProperty):
+            raise sa_exc.InvalidRequestError(
+                "back_populates on relationship '%s' refers to attribute '%s' "
+                "that is not a relationship.  The back_populates parameter "
+                "should refer to the name of a relationship on the target "
+                "class." % (self, other)
+            )
         # viewonly and sync_backref cases
         # 1. self.viewonly==True and other.sync_backref==True -> error
         # 2. self.viewonly==True and other.viewonly==False and
diff --git a/test/orm/test_relationships.py b/test/orm/test_relationships.py
index 867994866..77a218beb 100644
--- a/test/orm/test_relationships.py
+++ b/test/orm/test_relationships.py
@@ -2304,6 +2304,39 @@ class ManualBackrefTest(_fixtures.FixtureTest):
             configure_mappers,
         )
 
+    def test_back_propagates_not_relationship(self):
+        addr, Addr, users, User = (
+            self.tables.addresses,
+            self.classes.Address,
+            self.tables.users,
+            self.classes.User,
+        )
+
+        mapper(
+            User,
+            users,
+            properties={
+                "addresses": relationship(Addr, back_populates="user_id")
+            },
+        )
+
+        mapper(
+            Addr,
+            addr,
+            properties={
+                "users": relationship(User, back_populates="addresses")
+            },
+        )
+
+        assert_raises_message(
+            sa.exc.InvalidRequestError,
+            "back_populates on relationship 'User.addresses' refers to "
+            "attribute 'Address.user_id' that is not a relationship.  "
+            "The back_populates parameter should refer to the name of "
+            "a relationship on the target class.",
+            configure_mappers,
+        )
+
 
 class NoLoadBackPopulates(_fixtures.FixtureTest):
 
@@ -3146,6 +3179,7 @@ class ViewOnlySyncBackref(fixtures.MappedTest):
             return str(self.__dict__)
 
     cases = {
+        # (B_a_view, B_a_sync, A_bs_view, A_bs_sync)
         (0, 0, 0, 0): Case(),
         (0, 0, 0, 1): Case(Abs_evt=1),
         (0, 0, 1, 0): Case(),