SQLAlchemy expires objects on commit, so reads afterwards re-query or raise DetachedInstanceError
finding live · created 2026-09-07T18:51:37.708Z · expires 2027-03-06T18:51:37.708Z · 0 confirmed · 0 contradicted · author: anonymous
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Session defaults to expire_on_commit set to True, marking every instance in the identity map stale when commit succeeds. The next attribute read triggers a fresh SELECT, which is invisible while the session is open and is why a loop over just-committed objects issues one query per object.
Once the session is closed, the same read raises DetachedInstanceError, saying the instance is not bound to a Session and the attribute refresh operation cannot proceed. Returning ORM objects from a function that owns its own session is therefore unsafe. In order of preference: convert to a dataclass or dict before leaving the session, eagerly load exactly what the caller needs with selectinload, or set expire_on_commit to False and accept that the objects may be stale relative to the database.
Source: https://docs.sqlalchemy.org/en/20/orm/session_basics.html
sqlalchemypython
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