the warning is not a big deal but you probably dont want to be making these classes on the fly. mapping a class is not a quick operation internally, it's messy and somewhat questionable in highly concurrent situations.
On Wed, Sep 23, 2020, at 9:30 PM, [email protected] wrote: > Gotcha. > > Should I be worried about this warning or the approach of defining a > transient class to solve my problem (at least until 1.4 comes out): > SAWarning: This declarative base already contains a class with the same class > name and module name as my_app.graphql.queries.ATmp, and will be replaced in > the string-lookup table > On Wednesday, September 23, 2020 at 4:20:01 PM UTC-4 Mike Bayer wrote: >> __ >> yeah I don't have a solution to that problem right now, as mapped attributes >> are only a class-bound concept and there is no concept of an arbitrary >> attribute on an object that's not associated with a class-level mapped >> attribute. >> >> I think this problem long term would be solved more through some kind of >> @property selector that works from a class and is not specific to mapping. >> >> >> On Wed, Sep 23, 2020, at 8:51 PM, [email protected] wrote: >>> Understood. I was thinking though some sort of alias would be an >>> interesting solution to the problem outlined about `contains_eager` as well: >>> >Keep in mind that when we load only a subset of objects into a collection, >>> >that collection no longer represents what’s actually in the database. >>> In that rather than re-using a property which does have specific meaning, a >>> new property could be created that explicitly has different meaning. >>> On Wednesday, September 23, 2020 at 3:21:23 PM UTC-4 Mike Bayer wrote: >>>> __ >>>> A.bs only goes to the "bs" collection on an A. there's no eagerloading >>>> that puts the collection on some other arbitrary place. >>>> >>>> On Wed, Sep 23, 2020, at 6:03 PM, [email protected] wrote: >>>>> Cool, yes I think that is what I am looking for. Is there any way to >>>>> alias the relationship (as read only) to: 1. allow for multiple different >>>>> filters of the same property and 2. make sure when I read the value (in >>>>> another place in the code), I have confidence the filter was applied? >>>>> >>>>> something like (I made up the syntax): >>>>> q = session.query(A).options(selectinload(A.bs).and_(B.some_field == >>>>> value).as(f'bs_filtered_by_{value}') >>>>> ... >>>>> for a in q: >>>>> for b in a.bs_filtered_by_xxxx: >>>>> .... >>>>> >>>>> >>>>> On Wednesday, September 23, 2020 at 12:21:41 PM UTC-4 Mike Bayer wrote: >>>>>> >>>>>> >>>>>> On Wed, Sep 23, 2020, at 4:17 PM, [email protected] wrote: >>>>>>> I actually don't really care that much to have the attribute remain >>>>>>> dynamic. In fact there is only one *specific* filtering that I want to >>>>>>> apply to it, but that filtering will vary from (web) request to (web) >>>>>>> request. This is what made me think of using contains_eager. >>>>>>> >>>>>>> Right now this is the best solution I have come up with, which is to >>>>>>> define a temporary class that extends A and add to that class a new >>>>>>> relationship with the custom filter applied. I then specify to >>>>>>> selectinload that property. Is there a better way to do this? >>>>>> >>>>>> I would still use a separate relationship on the same class, you can >>>>>> always make a @hybrid_property that switches between the two >>>>>> relationships depending on what you want to do. >>>>>> >>>>>> In version 1.4, which will be in betas as soon as I can get a huge >>>>>> amount of new docs written, you will have a potentially better option >>>>>> for this which is the PropComparator.and_() operator. you can play with >>>>>> this now from git master if you were interested: >>>>>> >>>>>> https://docs.sqlalchemy.org/en/14/orm/loading_relationships.html#adding-criteria-to-loader-options >>>>>> >>>>>> that way you'd say: >>>>>> >>>>>> session.query(A).options(selectinload(A.bs).and_(B.some_field == value)) >>>>>> >>>>>> that might be what you're waiting for here >>>>>> >>>>>> >>>>>>> >>>>>>> >>>>>>> # Run this code for each web request, reading some_field_value from the >>>>>>> value the client specifies in the request: >>>>>>> some_field_value = ... >>>>>>> >>>>>>> class ATmp(A): >>>>>>> bs_temp = relationship( >>>>>>> lambda: models.B, >>>>>>> primaryjoin=( >>>>>>> (models.A.id <http://models.a.id/> == models.B.a_id) >>>>>>> & (models.B.some_field == some_field_value) >>>>>>> ), >>>>>>> ) >>>>>>> >>>>>>> q = return db.session.query(ATmp).options(selectinload(cls.bs_temp)) >>>>>>> # iterate over the q (which in iterable of "A"s) and for each A, >>>>>>> iterate over the bs_temp, which is a filtered collection of Bs. >>>>>>> >>>>>>> This also leads to a warning: >>>>>>> SAWarning: This declarative base already contains a class with the same >>>>>>> class name and module name as my_app.graphql.queries.ATmp, and will be >>>>>>> replaced in the string-lookup table >>>>>>> >>>>>>> though it does seem to work (I am able to avoid n+1 and do the >>>>>>> filtering in the DB). >>>>>>> On Wednesday, September 23, 2020 at 8:10:44 AM UTC-4 Mike Bayer wrote: >>>>>>>> >>>>>>>> >>>>>>>> On Wed, Sep 23, 2020, at 5:43 AM, [email protected] wrote: >>>>>>>>> Let's say I have a model with a one to many relationship as such: >>>>>>>>> class A(Base): >>>>>>>>> id = ... >>>>>>>>> >>>>>>>>> class B(Base): >>>>>>>>> id = ... >>>>>>>>> some_field = .... >>>>>>>>> a_id = Column(ForeignKey(A.id)... >>>>>>>>> a = relationship(A, backref=backref('bs', lazy='dynamic')) >>>>>>>>> >>>>>>>>> I can define a method on A: >>>>>>>>> class A(Base): >>>>>>>>> ... >>>>>>>>> def get_b_with_some_field(self, some_field): >>>>>>>>> return self.bs.filter(B.some_field==some_field) >>>>>>>>> >>>>>>>>> to get all b's that have a certain value of `some_field`. >>>>>>>>> >>>>>>>>> Is there any way to accomplish this with eager fetching to avoid the >>>>>>>>> n+1 select problem that will occur if I want to query for a lot of >>>>>>>>> `A`s and then iterate over the collection and for each call >>>>>>>>> `get_b_with_some_field` with the same value of `some_field`?' >>>>>>>> >>>>>>>> if you want to have that attribute remain on "dynamic" then you'd need >>>>>>>> to define a second relationship where you can use normal eager >>>>>>>> fetching strategies, and then use that for those cases. >>>>>>>> >>>>>>>> IMO "dynamic" is not really worth it, you can get the same queries >>>>>>>> more programmatically by using query(B).filter(with_parent(some_a, >>>>>>>> A.bs)). >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> One option is to to change relationship to from `lazy='dynamic'` to >>>>>>>>> `lazy='subquery'` or ``lazy='selectin'`` and then implement the >>>>>>>>> filtering in `get_b_with_some_field` in Python. This will address the >>>>>>>>> n+1 select problem, but will cause pulling extra data from the >>>>>>>>> database (and extra work in Python). >>>>>>>>> >>>>>>>>> I thought `contains_eager` >>>>>>>>> <https://docs.sqlalchemy.org/en/13/orm/loading_relationships.html?highlight=contains_eager#using-contains-eager-to-load-a-custom-filtered-collection-result> >>>>>>>>> might be relevant; however, I only see it being mentioned in the >>>>>>>>> case of joined loads. >>>>>>>>> >>>>>>>>> The reason I am looking for this functionality is I am defining a >>>>>>>>> graphql API that looks like the following: >>>>>>>>> type query { >>>>>>>>> as: [A!! >>>>>>>>> } >>>>>>>>> >>>>>>>>> type A { >>>>>>>>> ... >>>>>>>>> bs(some_field: String): [B!]! >>>>>>>>> } >>>>>>>>> >>>>>>>>> type B { >>>>>>>>> ... >>>>>>>>> some_field: String! >>>>>>>>> } >>>>>>>>> where I would like to be able to specify a filter on the `bs` >>>>>>>>> relationship from `A`. I would ideally like to 1. avoid the n+1 >>>>>>>>> select issue and 2. perform the some_field filtering at the database >>>>>>>>> level, and 3. leverage as much of the ORM as possible ;-) >>>>>>>>> >>>>>>>>> Is it possible to do this within SQLA? >>>>>>>>> >>>>>>>>> -- >>>>>>>>> SQLAlchemy - >>>>>>>>> The Python SQL Toolkit and Object Relational Mapper >>>>>>>>> >>>>>>>>> http://www.sqlalchemy.org/ >>>>>>>>> >>>>>>>>> To post example code, please provide an MCVE: Minimal, Complete, and >>>>>>>>> Verifiable Example. See http://stackoverflow.com/help/mcve for a full >>>>>>>>> description. >>>>>>>>> --- >>>>>>>>> You received this message because you are subscribed to the Google >>>>>>>>> Groups "sqlalchemy" group. >>>>>>>>> To unsubscribe from this group and stop receiving emails from it, >>>>>>>>> send an email to [email protected]. >>>>>>>>> To view this discussion on the web visit >>>>>>>>> https://groups.google.com/d/msgid/sqlalchemy/55c7b3a6-bfee-45b6-83bc-25185bf7af87n%40googlegroups.com >>>>>>>>> >>>>>>>>> <https://groups.google.com/d/msgid/sqlalchemy/55c7b3a6-bfee-45b6-83bc-25185bf7af87n%40googlegroups.com?utm_medium=email&utm_source=footer>. >>>>>>>> >>>>>>> >>>>>>> -- >>>>>>> SQLAlchemy - >>>>>>> The Python SQL Toolkit and Object Relational Mapper >>>>>>> >>>>>>> http://www.sqlalchemy.org/ >>>>>>> >>>>>>> To post example code, please provide an MCVE: Minimal, Complete, and >>>>>>> Verifiable Example. See http://stackoverflow.com/help/mcve for a full >>>>>>> description. >>>>>>> --- >>>>>>> You received this message because you are subscribed to the Google >>>>>>> Groups "sqlalchemy" group. >>>>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>>>> an email to [email protected]. >>>>>>> To view this discussion on the web visit >>>>>>> https://groups.google.com/d/msgid/sqlalchemy/e20cd72d-796f-4e99-a91d-55f4252f5fd6n%40googlegroups.com >>>>>>> >>>>>>> <https://groups.google.com/d/msgid/sqlalchemy/e20cd72d-796f-4e99-a91d-55f4252f5fd6n%40googlegroups.com?utm_medium=email&utm_source=footer>. >>>>>> >>>>> >>>>> -- >>>>> SQLAlchemy - >>>>> The Python SQL Toolkit and Object Relational Mapper >>>>> >>>>> http://www.sqlalchemy.org/ >>>>> >>>>> To post example code, please provide an MCVE: Minimal, Complete, and >>>>> Verifiable Example. See http://stackoverflow.com/help/mcve for a full >>>>> description. >>>>> --- >>>>> You received this message because you are subscribed to the Google Groups >>>>> "sqlalchemy" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send an >>>>> email to [email protected]. >>>>> To view this discussion on the web visit >>>>> https://groups.google.com/d/msgid/sqlalchemy/077fe551-e829-4da0-8a70-e65933ec3446n%40googlegroups.com >>>>> >>>>> <https://groups.google.com/d/msgid/sqlalchemy/077fe551-e829-4da0-8a70-e65933ec3446n%40googlegroups.com?utm_medium=email&utm_source=footer>. >>>> >>> >>> -- >>> SQLAlchemy - >>> The Python SQL Toolkit and Object Relational Mapper >>> >>> http://www.sqlalchemy.org/ >>> >>> To post example code, please provide an MCVE: Minimal, Complete, and >>> Verifiable Example. See http://stackoverflow.com/help/mcve for a full >>> description. >>> --- >>> You received this message because you are subscribed to the Google Groups >>> "sqlalchemy" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to [email protected]. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/sqlalchemy/4681fdf3-12d7-4f01-b2b4-149623cb92cbn%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/sqlalchemy/4681fdf3-12d7-4f01-b2b4-149623cb92cbn%40googlegroups.com?utm_medium=email&utm_source=footer>. >> > > -- > SQLAlchemy - > The Python SQL Toolkit and Object Relational Mapper > > http://www.sqlalchemy.org/ > > To post example code, please provide an MCVE: Minimal, Complete, and > Verifiable Example. See http://stackoverflow.com/help/mcve for a full > description. > --- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sqlalchemy/20ba0564-e7b7-4c4d-93f3-a9e668b9f0dbn%40googlegroups.com > > <https://groups.google.com/d/msgid/sqlalchemy/20ba0564-e7b7-4c4d-93f3-a9e668b9f0dbn%40googlegroups.com?utm_medium=email&utm_source=footer>. -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. 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