On Mon, Jan 11, 2021, at 10:20 PM, RexE wrote:
> I'm changing my framework to use the SQLAlchemy declarative system
> internally. However, I want to keep the API the same. Here is how users of my
> framework declare a foreign key:
>
> from myframework import Model, Link
>
> class Bar(Model)
>
> class Foo(Model):
> bar = Link(Bar)
>
> At first I thought I could simply change the implementation of Link to this:
>
> def Link(cls):
> return relationship(cls.__name__)
>
> But actually I see that in SQLAlchemy I also need an Integer column that
> contains the id. So, I think I would need to patch the class at runtime to
> ensure these 2 attributes are defined. First, I would make a simple
> definition of Link to store the class it points to:
>
> class Link:
> def __init__(self, cls):
> self.cls = cls
>
> Then after I import the user's module, I patch all subclasses of Model:
>
> for cls in Model.__subclasses__():
> for k, v in list(cls.__dict__.items()):
> if isinstance(v, Link):
> ClsName = v.cls.__name__
> setattr(cls, k, relationship(f'{cls.__module__}.{ClsName}'))
> setattr(
> cls,
> f'{k}_id',
> Column(
> Integer,
> ForeignKey(f'{cls.__tablename__}_{ClsName.lower()}.id'),
> ),
> )
>
> However, I get this:
>
> sqlalchemy.exc.NoReferencedTableError: Foreign key associated with column
> 'live_bid.player_id' could not find table 'live_bid_player' with which to
> generate a foreign key to target column 'id'
>
> I guess I am patching it too late. My next idea is to put this patching code
> inside the metaclass of Model, but before I go too far down the wrong path I
> wanted to ask here if there is a better way :)
Likely patching too early. For this kind of thing you want to use an event
like "mapper_configured" , which will give you a space where a particular
mapper is all set up, all the Table objects needed should have been defined,
and you can add additional attributes. there's a ten-year-old example of what
you are trying to do at
https://techspot.zzzeek.org/2011/05/17/magic-a-new-orm/. the code there seems
to be mostly still how things work.
>
> Thank you!
>
> --
> 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.
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--
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.
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