OK so you are explicitly worrying about a one-to-many relationship that should
be one-to-one, or vice versa, that is, you aren't worried about FKs or
remote_side setting up the entirely wrong M2O / O2M for a relationship.
However luckily, the only issue with any of this is having that argument
available and fortunately it looks like I got around to adding info to
relationship(), so you can check / validate whatever you want, including if the
"direction" got set up as expected or whatever other things you want to put
into that info. here's o2o:
from sqlalchemy import Column
from sqlalchemy import create_engine
from sqlalchemy import event
from sqlalchemy import ForeignKey
from sqlalchemy import Integer
from sqlalchemy import String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy.orm import Session
Base = declarative_base()
class A(Base):
__tablename__ = "a"
id = Column(Integer, primary_key=True)
data = Column(String)
b = relationship("B", back_populates="a", uselist=False)
class B(Base):
__tablename__ = "b"
id = Column(Integer, primary_key=True)
a_id = Column(ForeignKey("a.id"))
data = Column(String)
a = relationship("A", back_populates="b", info={"one_to_one": True})
@event.listens_for(Base, "mapper_configured", propagate=True)
def _validate(mapper, cls):
for rel in mapper.relationships:
if "one_to_one" in rel.info:
assert rel.mapper.attrs[rel.back_populates].uselist == (
not rel.info["one_to_one"]
)
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
s = Session(e)
s.add(A(b=B()))
s.commit()
On Wed, Feb 5, 2020, at 5:15 PM, Jonathan Vanasco wrote:
>
>
> On Wednesday, February 5, 2020 at 4:50:36 PM UTC-5, Mike Bayer wrote:
>> what conditions would cause the "uselist" to be incorrect?
>
>
> If `Foo.bars` declares:
> uselist=True,
> back_populates_uselist=False
>
> but `Bar.foo` declares:
> uselist=True,
> back_populates_uselist=True
>
> I want to catch `Foo.bars` specified `back_populates_uselist=False`, but the
> back_populates relationship `Bar.foo` specified `uselist=True`.
>
> i.e.. each side of the relationship agrees they are in a one-to-many or
> one-to-one relationship, instead of them independently defining only their
> side.
>
>
>
>
>
> --
> 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/3219e8a7-63e4-446e-8eef-641b3d86b339%40googlegroups.com
>
> <https://groups.google.com/d/msgid/sqlalchemy/3219e8a7-63e4-446e-8eef-641b3d86b339%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/32bddc06-9ddf-4604-83e0-d9a91a971c7c%40www.fastmail.com.
