fix: EventSession.commit() discards eager-loaded relations on watched models

src/fastapi_toolsets/models/watched.py

@@ -8,6 +8,7 @@ from typing import Any
 from sqlalchemy import event, select, tuple_
 from sqlalchemy import inspect as sa_inspect
 from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import selectinload
 from sqlalchemy.orm.attributes import set_committed_value as _sa_set_committed_value
 
 from ..logger import get_logger
@@ -189,17 +190,44 @@ async def _invoke_callback(
         await result
 
 
+def _loaded_relationships(obj: Any) -> set[str]:
+    """Relationship keys currently loaded on *obj*."""
+    state = sa_inspect(obj)
+    unloaded = state.unloaded
+    return {
+        rel.key
+        for rel in state.mapper.relationships
+        if rel.key not in unloaded and rel.lazy not in ("dynamic", "write_only")
+    }
+
+
+def _snapshot_loaded_relationships(session: Any) -> dict[int, set[str]]:
+    """Record loaded relationships for the tracked objects, keyed by ``id``."""
+    objs = list(session.info.get(_SESSION_CREATES, []))
+    objs += [obj for obj, _ in session.info.get(_SESSION_UPDATES, {}).values()]
+    return {id(obj): _loaded_relationships(obj) for obj in objs}
+
+
 async def _batch_reload(
-    session: AsyncSession, model: type, pk_tuples: list[tuple[Any, ...]]
+    session: AsyncSession,
+    model: type,
+    objs: list[Any],
+    preloaded: dict[int, set[str]],
 ) -> None:
-    """Re-populate all rows of *model* identified by *pk_tuples* in one round trip."""
+    """Re-populate all rows of *model* in one round trip."""
     pk_cols = sa_inspect(model, raiseerr=True).primary_key
+    pk_tuples = [sa_inspect(obj).key[1] for obj in objs]
     where = (
         pk_cols[0].in_([pk[0] for pk in pk_tuples])
         if len(pk_cols) == 1
         else tuple_(*pk_cols).in_(pk_tuples)
     )
     q = select(model).where(where).execution_options(populate_existing=True)
+    loaded: set[str] = set()
+    for obj in objs:
+        loaded |= preloaded.get(id(obj), set())
+    if loaded:
+        q = q.options(*(selectinload(getattr(model, key)) for key in loaded))
     await session.execute(q)
 
 
@@ -207,6 +235,7 @@ class EventSession(AsyncSession):
     """AsyncSession subclass that dispatches lifecycle callbacks after commit."""
 
     async def commit(self) -> None:
+        preloaded = _snapshot_loaded_relationships(self)
         await super().commit()
 
         creates: list[Any] = self.info.pop(_SESSION_CREATES, [])
@@ -249,25 +278,25 @@ class EventSession(AsyncSession):
         # session.get() per object.
         create_items: list[Any] = []
         update_items: list[tuple[Any, dict[str, dict[str, Any]]]] = []
-        pk_by_type: dict[type, list[tuple[Any, ...]]] = {}
+        objs_by_type: dict[type, list[Any]] = {}
 
         for obj in creates:
             state = sa_inspect(obj, raiseerr=False)
             if state is None or state.detached or state.transient:  # pragma: no cover
                 continue
             create_items.append(obj)
-            pk_by_type.setdefault(type(obj), []).append(state.key[1])
+            objs_by_type.setdefault(type(obj), []).append(obj)
 
         for obj, changes in field_changes.values():
             state = sa_inspect(obj, raiseerr=False)
             if state is None or state.detached or state.transient:  # pragma: no cover
                 continue
             update_items.append((obj, changes))
-            pk_by_type.setdefault(type(obj), []).append(state.key[1])
+            objs_by_type.setdefault(type(obj), []).append(obj)
 
-        for model, pk_tuples in pk_by_type.items():
+        for model, objs in objs_by_type.items():
             try:
-                await _batch_reload(self, model, pk_tuples)
+                await _batch_reload(self, model, objs, preloaded)
             except Exception as exc:
                 _logger.error(_CALLBACK_ERROR_MSG, exc_info=exc)
 

tests/test_models.py

@@ -6,9 +6,16 @@ from types import SimpleNamespace
 from unittest.mock import patch
 
 import pytest
-from sqlalchemy import String
+from sqlalchemy import ForeignKey, String, select
+from sqlalchemy import inspect as sa_inspect
 from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
-from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
+from sqlalchemy.orm import (
+    DeclarativeBase,
+    Mapped,
+    mapped_column,
+    relationship,
+    selectinload,
+)
 
 import fastapi_toolsets.models.watched as _watched_module
 from fastapi_toolsets.models import (
@@ -107,6 +114,27 @@ async def _watched_on_update(obj, event_type, changes):
     _test_events.append({"event": "update", "obj_id": obj.id, "changes": changes})
 
 
+class RelTarget(MixinBase, UUIDMixin):
+    __tablename__ = "mixin_rel_targets"
+
+    name: Mapped[str] = mapped_column(String(50))
+
+
+class RelOwner(MixinBase, UUIDMixin):
+    """Watched model with a relationship, to check eager loads survive commit."""
+
+    __tablename__ = "mixin_rel_owners"
+
+    title: Mapped[str] = mapped_column(String(50))
+    target_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("mixin_rel_targets.id"))
+    target: Mapped[RelTarget] = relationship()
+
+
+@listens_for(RelOwner, [ModelEvent.CREATE, ModelEvent.UPDATE])
+async def _rel_owner_handler(obj, event_type, changes):
+    _test_events.append({"event": event_type.value, "obj_id": obj.id})
+
+
 class WatchAllModel(MixinBase, UUIDMixin):
     """Model without __watched_fields__ — watches all mapped fields by default."""
 
@@ -355,6 +383,62 @@ async def mixin_session_maker():
         await engine.dispose()
 
 
+class TestEventSessionPreservesEagerLoads:
+    """EventSession.commit() must not discard relations an eager load populated."""
+
+    async def _seed_eager(self, session):
+        target = RelTarget(name="t")
+        session.add(target)
+        await session.flush()
+        owner = RelOwner(title="o", target_id=target.id)
+        session.add(owner)
+        await session.flush()
+        loaded = (
+            await session.execute(
+                select(RelOwner)
+                .where(RelOwner.id == owner.id)
+                .options(selectinload(RelOwner.target))
+            )
+        ).scalar_one()
+        assert "target" not in sa_inspect(loaded).unloaded
+        return loaded
+
+    @pytest.mark.anyio
+    async def test_eager_load_survives_commit(self, mixin_session):
+        """expire_on_commit=False: the reload must not expire the relation."""
+        owner = await self._seed_eager(mixin_session)
+
+        await mixin_session.commit()
+
+        assert "target" not in sa_inspect(owner).unloaded
+        assert owner.target.name == "t"
+
+    @pytest.mark.anyio
+    async def test_eager_load_survives_commit_expire_on_commit(
+        self, mixin_session_expire
+    ):
+        """expire_on_commit=True: what was loaded must be recorded before the commit."""
+        owner = await self._seed_eager(mixin_session_expire)
+
+        await mixin_session_expire.commit()
+
+        assert "target" not in sa_inspect(owner).unloaded
+        assert owner.target.name == "t"
+
+    @pytest.mark.anyio
+    async def test_unloaded_relation_stays_unloaded(self, mixin_session):
+        """Only what was loaded is restored: the reload must not eager-load extra."""
+        target = RelTarget(name="t")
+        mixin_session.add(target)
+        await mixin_session.flush()
+        owner = RelOwner(title="o", target_id=target.id)
+        mixin_session.add(owner)
+
+        await mixin_session.commit()
+
+        assert "target" in sa_inspect(owner).unloaded
+
+
 class TestUUIDMixin:
     @pytest.mark.anyio
     async def test_uuid_generated_by_db(self, mixin_session):
@@ -1013,10 +1097,10 @@ class TestEventCallbacks:
 
         real_batch_reload = _watched_module._batch_reload
 
-        async def racing_batch_reload(session, model, pk_tuples):
+        async def racing_batch_reload(session, model, objs, preloaded):
-            if any(pk[0] == doomed_id for pk in pk_tuples):
+            if any(getattr(o, "id", None) == doomed_id for o in objs):
                 await kill_doomed_row_once()
-            return await real_batch_reload(session, model, pk_tuples)
+            return await real_batch_reload(session, model, objs, preloaded)
 
         # Patch the batched reload EventSession.commit() uses to pick up
         # server defaults, so this test still exercises the race.
@@ -1039,7 +1123,7 @@ class TestEventCallbacks:
         obj = WatchedModel(status="active", other="x")
         mixin_session.add(obj)
 
-        async def failing_batch_reload(session, model, pk_tuples):
+        async def failing_batch_reload(session, model, objs, preloaded):
             raise RuntimeError("reload failed")
 
         with (