hey there -
these mappings are pretty good, as is always the case I cannot predict why an
issue is occurring, or usually even understand the issue, without running the
code. your code is pretty runnable with a few imports added so that's great.
however adding an assertion for the condition you describe "m2.daughter is not
None" is not reproducible on my end. Try out the script below and see if
you have different results.
from sqlalchemy import Column
from sqlalchemy import create_engine
from sqlalchemy import ForeignKey
from sqlalchemy import Integer
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy.orm import Session
Base = declarative_base()
class Super(Base):
__tablename__ = "super"
id = Column(Integer, primary_key=True)
class Mama(Super):
__tablename__ = "mama"
id = Column(Integer, ForeignKey("super.id"), primary_key=True)
daughter_id = Column(Integer, ForeignKey("daughter.id"))
daughter = relationship(
"Daughter", foreign_keys=[daughter_id], back_populates="mama"
)
class Daughter(Super):
__tablename__ = "daughter"
id = Column(Integer, ForeignKey("super.id"), primary_key=True)
mama = relationship(
"Mama",
foreign_keys=[Mama.daughter_id],
uselist=False,
back_populates="daughter",
)
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
session = Session(e)
m1 = Mama()
m2 = Mama()
d1 = Daughter()
d2 = Daughter()
session.add(m1)
session.add(m2)
session.add(d1)
session.add(d2)
session.commit()
m1.daughter = d1
m2.daughter = d2
session.commit()
m1.daughter = d2
session.commit()
assert m2.daughter is None
On Fri, Dec 18, 2020, at 2:01 AM, 'Sören Textor' via sqlalchemy wrote:
> Hello
> I have a huge problem with süecific "one to one" relation.
>
> Woking (it's the tutorial code)
>
> class Son(db.Model):
> __tablename__ = 'son'
> id = db.Column(db.Integer, primary_key=True)
> papa_id = db.Column(db.Integer, db.ForeignKey('papa.id'))
> papa = db.relationship("Papa", foreign_keys=[papa_id],
> back_populates="son")
>
> class Papa(db.Model):
> __tablename__ = 'papa'
> id = db.Column(db.Integer, primary_key=True)
> son = db.relationship("Son", uselist=False, back_populates="papa")
>
> main:
> p1 = Papa()
> p2 = Papa()
> s1 = Son()
> s2 = Son()
>
> db.session.add(p1)
> db.session.add(p2)
> db.session.add(s1)
> db.session.add(s2)
>
> db.session.commit()
> p1.son = s1
> p2.son = s2
> db.session.commit()
> p1.son = s2
> db.session.commit()
>
> Works like a charm. afterwards every relation is correct
>
> My code (I have to use a super class, that's the only difference):
>
> class Super(db.Model):
> __tablename__ = 'super'
> id = db.Column(db.Integer, primary_key=True)
>
> class Mama(Super):
> __tablename__ = 'mama'
> id = db.Column(db.Integer, db.ForeignKey('super.id'), primary_key=True)
>
> daughter_id = db.Column(db.Integer, db.ForeignKey('daughter.id'))
> daughter = db.relationship("Daughter", foreign_keys=[daughter_id],
> back_populates="mama")
>
> class Daughter(Super):
> __tablename__ = 'daughter'
> id = db.Column(db.Integer, db.ForeignKey('super.id'), primary_key=True)
> mama = db.relationship("Mama", foreign_keys=[Mama.daughter_id],
> uselist=False, back_populates="daughter")
>
> main:
> m1 = Mama()
> m2 = Mama()
> d1 = Daughter()
> d2 = Daughter()
>
> db.session.add(m1)
> db.session.add(m2)
> db.session.add(d1)
> db.session.add(d2)
> db.session.commit()
>
> m1.daughter = d1
> m2.daughter = d2
> db.session.commit()
>
> m1.daughter = d2
> db.session.commit()
>
> everything is correct EXCEPT:
> *m2.daughter! *it still points on d2 instead of None. And the table contains
> still the daughter_id of d2.
>
> Thus, what foreign key did I miss?
>
> All the best and stay healthy!
> SirAnn
>
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
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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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