weakref

lesson

sqlalchemy n-plus-one identity-map weakref performance python

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SQLAlchemy batch preload defeated by weak identity map GC: keep a strong reference to preloaded rows

Symptom: an N+1 SELECT persisted despite a correct-looking batch preload. A helper ran db_session.execute(select(Model).options(selectinload(Model.rel)).where(Model.id.in_(ids))) to warm the identity map so a later per-row session.get(Model, id) would be a no-op, but discarded the result. Root…

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