Test for sa_relationship.

tests/test_main.py

@@ -1,8 +1,9 @@
-from typing import Optional
+from typing import List, Optional
 
 import pytest
 from sqlalchemy.exc import IntegrityError
-from sqlmodel import Field, Session, SQLModel, create_engine
+from sqlalchemy.orm import RelationshipProperty
+from sqlmodel import Field, Relationship, Session, SQLModel, create_engine
 
 
 def test_should_allow_duplicate_row_if_unique_constraint_is_not_passed(clear_sqlmodel):
@@ -91,3 +92,36 @@ class Hero(SQLModel, table=True):
             session.add(hero_2)
             session.commit()
             session.refresh(hero_2)
+
+
+def test_sa_relationship(clear_sqlmodel):
+    """Test https://github.com/tiangolo/sqlmodel/issues/315#issuecomment-1272122306"""
+
+    class Team(SQLModel, table=True):
+        id: Optional[int] = Field(default=None, primary_key=True)
+        name: str = Field(unique=True)
+        heroes: List["Hero"] = Relationship(
+            sa_relationship=RelationshipProperty("Hero", back_populates="team")
+        )
+
+    class Hero(SQLModel, table=True):
+        id: Optional[int] = Field(default=None, primary_key=True)
+        name: str = Field(unique=True)
+        team_id: Optional[int] = Field(default=None, foreign_key="team.id")
+        team: Optional[Team] = Relationship(
+            sa_relationship=RelationshipProperty("Team", back_populates="heroes")
+        )
+
+    team_preventers = Team(name="Preventers")
+    hero_rusty_man = Hero(name="Rusty-Man", team=team_preventers)
+
+    engine = create_engine("sqlite://", echo=True)
+
+    SQLModel.metadata.create_all(engine)
+
+    with Session(engine) as session:
+        session.add(hero_rusty_man)
+        session.commit()
+        session.refresh(hero_rusty_man)
+        # The next statement should not raise an AttributeError
+        assert hero_rusty_man.team.name == "Preventers"