This example fails. Instead of assigning an objekt, I assign just the
daughters id ...
But I think that's "correct"?
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_id = d2.id #instead of m1.daughter = d2
session.commit()
assert m1.daughter is d2
assert m2.daughter is None # FAILS
assert m2.daughter_id is None #FAILS
SirAnn
------ Originalnachricht ------
Von: "Sören Textor" <[email protected]>
An: "[email protected]" <[email protected]>
Gesendet: 18.12.2020 16:52:35
Betreff: Re: [sqlalchemy] One to One relation problem
Hi Mike.
Thanks for answering. I‘ll check it out on monday.
We use MSSQL2016 and flask. That‘s the only difference I see at the
first look.
I‘ll send a detailed answer to the group afterwards. Without the super
class it also works fine. That‘s why I thought it is an issue with
foreign keys.
We are running the newest 1.3.x of SQLAlchemy.
Mike Bayer <[email protected]> schrieb am Fr. 18. Dez. 2020 um
16:31:
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
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