the recursion_depth feature on selectinload() is also very new and that is
actually a very complex and not very mature feature. If you only wanted to
apply additional options for N levels deep, you would build out separate
options for that, like:
options(
selectinload(Model.thing, recursion_depth=-1),
defaultload(Model.thing).selectinload(Model.otherthing).selectinload(Model.otherthing)
)
something like that
again, fairly esoteric stuff
On Fri, Sep 15, 2023, at 4:25 AM, Cornelis Poppema wrote:
> Hello Mike, thank you very much for the in-depth reply and providing a
> solution :)
>
> There is no specific reason that I posted in google groups, I did not visit
> the support page, this was just something I decided after thinking where to
> post first between googlegroups and stackoverflow, I will use github
> discussions when I open a new discussion in the future!
> Your workaround will help me continue so many many thanks. I thought I tried
> all variations, but I can only concede after seeing this work that I did not
> attempt adding the selectinload to the root options().
>
> It might warrant a new thread, but can you also tell me if there is a way to
> control the options() that sqlalchemy uses for the recursion of next_step ?
>
> Ie. I included this bit in the original post:
> ```
> .options(
> selectinload(StepModel.next_step, recursion_depth=-1),
> ...
> )
> ```
>
> and it would be helpful to know if I can chain the same options to next_step,
> so that step also has its actions and their relationships() eagerly available
> etc.
>
> PS
> FWIW the reason I included `raiseload("*")` in options() is because I am
> running async queries, and personally the error I will be confronted with
> trying to access lazy attributes is more helpful, so I've come to add it by
> default. Without raisedload(*) I would see:
> ```
> sqlalchemy.exc.MissingGreenlet: greenlet_spawn has not been called; can't
> call await_only() here. Was IO attempted in an unexpected place? (Background
> on this error at: https://sqlalche.me/e/20/xd2s)
> ```
>
> With the help of raisedload(*) I get to see:
> ```
> sqlalchemy.exc.InvalidRequestError: 'ServiceActionModel.service' is not
> available due to lazy='raise```
> ```
>
> This helps me tackle those cases more easily one-by-one.
>
> On Thursday, 14 September 2023 at 15:30:23 UTC+2 Mike Bayer wrote:
>> __
>>
>>
>> On Thu, Sep 14, 2023, at 7:36 AM, Cornelis Poppema wrote:
>>> Hi all,
>>>
>>> I am new to sqlalchemy, I think the idea of what I am trying to achieve is
>>> relatively simple, but I can't seem to figure out how to retrieve
>>> `.service` in the same query. I failed to find an example in the 2.0
>>> documentation for exactly this.
>>>
>>> My attempts have been to simply chain a .selectinload after the
>>> .selectin_polymorphic, ie.:
>>>
>>> ```python
>>> .options(
>>> selectinload(StepModel.next_step, recursion_depth=-1),
>>> selectinload(StepModel.actionbases).selectin_polymorphic(
>>> [
>>> ServiceActionModel,
>>> ],
>>> )
>>> .selectinload(ServiceActionModel.service),
>>> raiseload("*"),
>>> )
>>> ```
>>>
>>> This gives the error:
>>>
>>> ```
>>> /usr/local/lib/python3.11/site-packages/sqlalchemy/orm/strategy_options.py:2442:
>>> in _raise_for_does_not_link
>>> raise sa_exc.ArgumentError(
>>> E sqlalchemy.exc.ArgumentError: ORM mapped entity or attribute
>>> "ServiceActionModel.service" does not link from relationship
>>> "StepModel.actionbases". Did you mean to use
>>> "StepModel.actionbases.of_type(ServiceActionModel)"?
>>> ```
>>>
>>
>> Hi -
>>
>> A few up front things, is it possible you can post these questions that have
>> a lot of code on github discussions? That's at
>> https://github.com/sqlalchemy/sqlalchemy/discussions . I'm sort of
>> wondering how new users are still arriving here at the mailing list, did you
>> find this list via the support page at
>> https://www.sqlalchemy.org/support.html ? I would want to change the
>> verbiage there to please refer people to GH discussions instead.
>> Especially with these advanced inheritance eager loading problems, which in
>> the majority of cases end up being real bugs in SQLAlchemy, as seems to be
>> the case here (at least, there is an inconsistency in the API that somehow
>> needs to be documented, or something).
>>
>> As for the question, first off this is really advanced usage and I've hardly
>> ever seen people using selectin_polymorphic(), much less deep within a chain
>> of loaders like this.
>>
>> The correct form for this load would follow from how it's described at
>> https://docs.sqlalchemy.org/en/20/orm/queryguide/inheritance.html#combining-additional-loader-options-with-selectin-polymorphic-subclass-loads
>> , where the ORM allows the selectin_polymorphic(Target, [TargetSubclassA])
>> to be a sibling to the appropriate relationship load,
>> selectinload(TargetSubclassA.elements). The example there places both of
>> these options comma-separated within select().options(). This is the
>> "inconsistent" part because I'm already surprised the ORM is allowing the
>> selectinload() to be present against TargetSubclassA when that's not one of
>> the primary entities in the select().
>>
>> However in your case, you are coming off of a parent loader option already.
>> So following from this, the correct form based on a direct reading of those
>> docs would, *in theory*, be:
>>
>> select().options(
>> selectinload(Parent.target).options(
>> selectin_polymorphic(Target, [TargetSubclassA]),
>> selectinload(TargetSubclassA.elements)
>> )
>> )
>>
>> that is, you can build up sibling options from a parent loader option using
>> another call to .options().
>>
>> however, this doesn't work; the validation of the loader chain
>> unsurprisingly notes that TargetSubclass is not linked from Parent.target,
>> and they'd like you to use of_type() instead. So I've made a bug for this
>> here: https://github.com/sqlalchemy/sqlalchemy/issues/10348 as something
>> has to change here, either the docs, or the usage pattern for
>> selectin_polymorphic(), or the error checks have to get a lot smarter to
>> figure this out and let this case pass, since it works fine the way you are
>> expecting if I just have it skip the error checking.
>>
>> What you can do now is use with_polymorphic() instead that is more
>> configurable for this kind of loader chain:
>>
>> TT = with_polymorphic(Target, [TargetSubclassA])
>> select().options(selectinload(Parent.target.of_type(TT).selectinload(TT.TargetSubclassA.elements)))
>>
>> discussion can continue at the issue above or a new github discussion,
>> thanks!
>>
>>
>
>
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> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
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> http://www.sqlalchemy.org/
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