What do transient, pending, persistent, expired, and detached mean in SQLAlchemy?

Connects SQLAlchemy object states to flush, commit, close, serialization, and later attribute access.

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A transient object has been constructed but is not in a Session. Adding it makes it pending; after a successful flush it becomes persistent and represents a database row in that Session. Expired means some loaded values have been marked to reload on access. Detached means the object is no longer associated with a Session, so unloaded or expired attributes cannot transparently load through that old Session.

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Connects SQLAlchemy object states to flush, commit, close, serialization, and later attribute access.

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Connects SQLAlchemy object states to flush, commit, close, serialization, and later attribute access.
A transient object has been constructed but is not in a Session. Adding it makes it pending; after a successful flush it becomes persistent and represents a database row in that Session. Expired means some loaded values have been marked to reload on access. Detached means the object is no longer associated with a Session, so unloaded or expired attributes cannot transparently load through that old Session.
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By default, commit expires persistent objects so later access can reflect a new transaction. That is useful inside a managed Session but surprising if an API returns ORM entities after the Session closes. I usually shape a response while the data boundary is active, explicitly load what is needed, and return a DTO or plain data. Disabling expire_on_commit can be a deliberate choice, especially in async code, but it trades automatic refresh for potentially stale in-memory values.

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Returning partially loaded entities after closing the Session
Keeping sessions open only for serialization
Using merge without understanding copied state

What do transient, pending, persistent, expired, and detached mean in SQLAlchemy?

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