it looks like you're trying to add an ORDER BY to the table that's only there
via joinedload(). That's *really* not something we anticipate and it would
be better if people proposed perhaps ad-hoc order_by expressions to be added to
common loader options like joinedload() and selectinload(), in the same way
that we offer ad-hoc WHERE criteria for these options now. as you are
probably aware, the current way to do "joinedload with custom criteria /
ordering / etc" is to write the query using outerjoin() and order_by()
normally, then use contains_eager().
the general thing we see here looks like when your "col_by_name()" routine
runs, it's getting a Column object that's associated with a different alias
than the one that is used when joinedload() writes out the joins. I'm not
sure offhand if the issue is in col_by_name() or something architectural that
makes the joinedload() join receive additional processing that isn't including
the order_by. It's hard for us to support this kind of transformation for
joined eager loads.
On Sat, Jun 10, 2023, at 12:34 PM, Lele Gaifax wrote:
> Hi,
>
> I spent some more time to improve support for SA 2 of one of my SA-based
> libraries[1] (the most ancient one, born with SA 0.5, fifteen years ago!):
> its goal is to provide a layer that made it easier to "expose" a SA
> query (either an ORM one or a Core select()) thru a web service,
> handling particular arguments to apply different kind of "refinements"
> such as ordering and filtering.
>
> One of the tests that exercise the "ordering" refinements fails, and I
> could not understand what is going wrong nor find a workaround.
>
> The following simple script builds an ORM query and prints its SQL:
>
> import sqlalchemy as sa
>
>
> SQLALCHEMY_VERSION = tuple(int(p) if p.isdigit() else p for p in
> sa.__version__.split('.'))
>
>
> metadata = sa.MetaData()
>
>
> if SQLALCHEMY_VERSION > (2, 0):
> from sqlalchemy.orm import DeclarativeBase
>
> class Base(DeclarativeBase):
> metadata = metadata
> else:
> from sqlalchemy.orm import declarative_base
>
> Base = declarative_base(metadata=metadata)
>
>
> class Person(Base):
> __tablename__ = 'persons'
>
> id = sa.Column(sa.Integer, primary_key=True)
> firstname = sa.Column(sa.String)
>
>
> class Pet(Base):
> __tablename__ = 'pets'
>
> id = sa.Column(sa.Integer, primary_key=True)
> name = sa.Column(sa.String)
> person_id = sa.Column(sa.Integer, sa.ForeignKey('persons.id'))
>
> person = sa.orm.relationship(Person,
> backref=sa.orm.backref('pets', order_by=id))
>
>
> engine = sa.create_engine('sqlite:///:memory:')
> Session = sa.orm.sessionmaker(bind=engine)
>
> metadata.create_all(engine)
>
>
> query =
> sa.orm.Query([Pet]).options(sa.orm.joinedload(Pet.person).load_only(Person.firstname))
> print(str(query))
>
> It emits the following output under both SA 1.4 and SA 2.0:
>
> SELECT pets.id AS pets_id, pets.name AS pets_name, pets.person_id
> AS pets_person_id, persons_1.id AS persons_1_id, persons_1.firstname AS
> persons_1_firstname
> FROM pets LEFT OUTER JOIN persons AS persons_1 ON persons_1.id =
> pets.person_id
>
>
> And now the problem: in short, when the library is asked to apply an
> "order by" on some column(s), it uses an utility function[2] to find a
> column given it's name in the particular query, and then it applies an
> `order_by()` the original query[3].
>
> So, appending the following lines to the script above:
>
> from metapensiero.sqlalchemy.proxy.utils import col_by_name
>
> col = col_by_name(query.statement, 'firstname')
>
> sorted_query = query.order_by(col)
> print(str(sorted_query))
>
> I get the following, expected, output under SA 1.4:
>
> SELECT pets.id AS pets_id, pets.name AS pets_name, pets.person_id
> AS pets_person_id, persons_1.id AS persons_1_id, persons_1.firstname AS
> persons_1_firstname
> FROM pets LEFT OUTER JOIN persons AS persons_1 ON persons_1.id =
> pets.person_id ORDER BY persons_1.firstname
>
> while under SA 2.0.15 I get this:
>
> SELECT pets.id AS pets_id, pets.name AS pets_name, pets.person_id
> AS pets_person_id, persons_1.id AS persons_1_id, persons_1.firstname AS
> persons_1_firstname
> FROM pets LEFT OUTER JOIN persons AS persons_1 ON persons_1.id =
> pets.person_id ORDER BY persons_2.firstname
>
> that obviously fails, with the following error:
>
> sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) no such
> column: persons_2.firstname
>
> Putting a breakpoint just before applying that `.order_by()` and
> inspecting the `col` returned by the function, I cannot spot any
> difference in the object, under both SA I see
>
> (Pdb) p col
> Column('firstname', String(), table=<anon_1>)
>
> Can you shed some light on what I can try to smooth this different
> behaviour?
>
> Thanks a lot in advance,
> bye, lele.
>
> [1] https://gitlab.com/metapensiero/metapensiero.sqlalchemy.proxy
> [2]
> https://gitlab.com/metapensiero/metapensiero.sqlalchemy.proxy/-/blob/8db2c398aaf8a0bd679557f630c5c8433a1f4572/src/metapensiero/sqlalchemy/proxy/utils.py#L44-98
> [3]
> https://gitlab.com/metapensiero/metapensiero.sqlalchemy.proxy/-/blob/8db2c398aaf8a0bd679557f630c5c8433a1f4572/src/metapensiero/sqlalchemy/proxy/sorters.py#L156-210
> --
> nickname: Lele Gaifax | Dire che Emacs è "conveniente" è come
> real: Emanuele Gaifas | etichettare l'ossigeno come "utile"
> l...@etour.tn.it | -- Rens Troost
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
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http://www.sqlalchemy.org/
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