joinedload().load_only() emits 2.0 warning

[Lele Gaifax]

Hi,

while upgrading one of my apps to SA 1.4, paying attention toward 2.0
compatibility, I found one single issue that I was not able to figure out
whether I'm doing something wrong or missed something in the excellent
migration guide.

All tests pass, but executing them with SQLALCHEMY_WARN_20 I noticed the
following message:

RemovedIn20Warning: Using strings to indicate column or relationship paths
in loader options is deprecated and will be removed in SQLAlchemy 2.0...

It was not so simple to isolate the culprit code, but I eventually found the
cause: here and there my app uses the load_only() option to load a subset of
the columns of related entities, and that's what upsets the compatibily check.

I'm attaching below a simple script that exhibits the problem (when executed
with SQLALCHEMY_WARN_20=1).

The documentation[1] shows a very similar usage, so I'm not sure where's the
problem. Maybe using joinedload(X.y).load_only(a, b), a and b cannot be column
names under 2.0, but should be Y.a and Y.b instead?

Thanks a lot for any hint,
ciao, lele.

[1] https://docs.sqlalchemy.org/en/14/orm/query.html#sqlalchemy.orm.Load.load_only

[Mike Bayer]

i can look later, if i forget after a day or so please post this to github discussions and/or issues where i will notice it better

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Attachments:

• test.py
  

[Federico Caselli]

Hi.

As the warning mebtions, the issue is that you are using the string name with load only instead of the column from the class.

In this load only from the file:

.load_only('firstname')))

[Lele Gaifax]

Federico Caselli <cfede...@gmail.com> writes:

> As the warning mebtions, the issue is that you are using the string name
> with load only instead of the column from the class.

Ok, so maybe we should explain the difference in the joinedload().load_only()
documentation? As said, the sample code attached to the generic load_only()
function documentation uses the string name.

ciao, lele.

[Federico Caselli]

There is no difference, it's the documentation that's outdated.

We should update that

[Lele Gaifax]

Federico Caselli <cfede...@gmail.com> writes:

> There is no difference, it's the documentation that's outdated.
>
> We should update that

I see, thank you for the clarification!

[Federico Caselli]

Updated here https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/2959

[Lele Gaifax]

Federico Caselli <cfede...@gmail.com> writes:

> Updated here https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/2959

Great, thank you!