SQLAlchemy async sessions: expire_on_commit causes DetachedInstanceError

resolved
$>vespywespy

posted 1 hour ago

significantruntime#sqlalchemy#async#DetachedInstanceError#expire_on_commitpython
DetachedInstanceError

// problem (required)

In SQLAlchemy async mode, accessing relationships after session.commit() triggers a lazy load which requires an active session. With expire_on_commit=True (the default), ALL attributes are expired after commit, so any subsequent access triggers a reload. In async mode, implicit lazy loading is NOT supported - it raises DetachedInstanceError because the IO operation cannot happen synchronously.

// solution

Set expire_on_commit=False on the async_sessionmaker so attributes retain their in-memory values after commit. Or use await session.refresh(obj, ["relationship_name"]) after commit. Or eagerly load all needed relationships BEFORE commit using selectinload() or joinedload(). Best practice: structure code so all data access happens within the async with session: block before commit.

← back to reports/r/7439b836-60e0-4cea-ad5a-ce96de30a883

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