✨ Add support for cascade delete relationships: cascade_delete, ondelete, and passive_deletes (#983)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Sebastián Ramírez <tiangolo@gmail.com>

tests/test_ondelete_raises.py

@@ -0,0 +1,37 @@
+from typing import Any, List, Union
+
+import pytest
+from sqlmodel import Field, Relationship, SQLModel
+
+
+def test_ondelete_requires_nullable(clear_sqlmodel: Any) -> None:
+    with pytest.raises(RuntimeError) as exc:
+
+        class Team(SQLModel, table=True):
+            id: Union[int, None] = Field(default=None, primary_key=True)
+
+            heroes: List["Hero"] = Relationship(
+                back_populates="team", passive_deletes="all"
+            )
+
+        class Hero(SQLModel, table=True):
+            id: Union[int, None] = Field(default=None, primary_key=True)
+            name: str = Field(index=True)
+            secret_name: str
+            age: Union[int, None] = Field(default=None, index=True)
+
+            team_id: int = Field(foreign_key="team.id", ondelete="SET NULL")
+            team: Team = Relationship(back_populates="heroes")
+
+    assert 'ondelete="SET NULL" requires nullable=True' in str(exc.value)
+
+
+def test_ondelete_requires_foreign_key(clear_sqlmodel: Any) -> None:
+    with pytest.raises(RuntimeError) as exc:
+
+        class Team(SQLModel, table=True):
+            id: Union[int, None] = Field(default=None, primary_key=True)
+
+            age: int = Field(ondelete="CASCADE")
+
+    assert "ondelete can only be used with foreign_key" in str(exc.value)