[ORM] Fetching columns that were assigned a SQL expression as part of INSERT...RETURNING and UPDATE...RETURNING

[univerio]

Suppose I have a PostgreSQL backend and I have the following class:

    class Foo(Base):

        id = Column(Integer, primary_key=True)

        updated_at = Column(DateTime)

and I do

    foo = Foo(updated_at=func.now())

    session.add(foo)

    session.flush()

    foo.id  # this is already loaded, no additional query emitted

    foo.updated_at  # this is not loaded, will cause an additional query to be emitted

Is it possible to have the SQLAlchemy ORM fetch the actual value of updated_at as part of the INSERT...RETURNING statement like it does for id, instead of leaving it unloaded and having to issue a second query when I access it?

Jack

[Mike Bayer]

use the eager_defaults flag:


http://docs.sqlalchemy.org/en/rel_1_0/orm/mapping_api.html?highlight=eager_defaults#sqlalchemy.orm.mapper.params.eager_defaults

http://docs.sqlalchemy.org/en/rel_0_9/changelog/migration_09.html#orm-can-efficiently-fetch-just-generated-insert-update-defaults-using-returning


not sure if this works for the ad-hoc set up updated_at, try it out.   if it's a server_default on the Column, should definitely work.

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[Jack Zhou]

Great! That worked, though I had to add server_default=FetchedValue() and server_onupdate=FetchedValue(). Would be nice if SQLAlchemy auto-detected this case, but no big deal otherwise.

Thanks!

Jack

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