SQLAlchemy: `db.refresh()` necessary after `db.commit()`?

[briantjt]

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According to FastAPI's SQLAlchemy tutorial, db.refresh() is called after db.commit(). However from SQLAlchemy's documentation:

Finally, all objects within the Session are expired as the transaction is closed out. This is so that when the instances are next accessed, either through attribute access or by them being present in the result of a SELECT, they receive the most recent state. This behavior may be controlled by the Session.expire_on_commit flag, which may be set to False when this behavior is undesirable.

So in this case, db.refresh() shouldn't be necessary as expire_on_commit defaults to True and the tutorial doesn't set this to False? Or does FastAPI/Pydantic do something to the ORM object that necessitates this?

[tusharsnx]

@brianjt
until there is no db.commit() the data that is fetched once remains in the memory and never accessed from the database but once db.commit() is executed, first access request of every data(in ORM it's an object) will be fetched from the database and remains in the memory until next db.commit(). Every subsequent query will fetch it from the memory instead of making another object for the same data. I never had to do db.refresh() after db.commit() but it could be useful in some cases.