On 04/03/2017 09:52 AM, Shane Carey wrote:
I am getting an error where delete orphan on a relationship seems to
happen even when the parent object is expunged.
I reproduced the issue in this example.
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import *
Base = declarative_base()
class Parent(Base):
__tablename__ = 'parent'
id = Column(Integer, primary_key=True)
children = relationship('Child', lazy='joined', backref='parent',
cascade='all, delete-orphan')
def dict(self):
return {
'id': self.id,
'children': [c.dict() for c in self.children]
}
class Child(Base):
__tablename__ = 'child'
parent_id = Column(None, ForeignKey(Parent.id), primary_key=True)
name = Column(String(8), primary_key=True)
def dict(self):
return {
'name': self.name
}
if __name__ == '__main__':
e = create_engine('sqlite:///orphan.db', echo=True)
Base.metadata.drop_all(e)
Base.metadata.create_all(e)
s = sessionmaker(e)()
p = Parent()
p.children = [Child(name=str(i)) for i in range(5)]
s.add(p)
s.commit()
p = s.query(Parent).one()
print(p.dict())
p.children = [Child(name=str(i)) for i in range(5, 10)]
print(p.dict())
s.expunge(p)
p = s.query(Parent).one()
print(p.dict())
The parent has no children after the expunge, is this intended or a bug?
Hi there -
OK, this is definitely more of a mindbender, and I don't know that
there's a way situations like these can have a little less cognitive
load on them. However, let me propose an alternate form of what we see
above - let's see if our expectations change:
p = Parent()
p.children = [Child(name=str(i)) for i in range(5)]
s.add(p)
s.commit()
p = s.query(Parent).one()
for child in p.children:
child.parent = None
for i in range(5, 10):
Child(name=str(i), parent=p)
s.expunge(p)
now, with the above, for the original Child 1-5, do we expect:
1. that they are also expunged? Why would that be, when they are no
longer associated with p?
2. that they be treated as non-orphans? Why would that be, when we have
set child.parent = None?
therefore, looking at it from the above perspective it seems to me that
they *should* be deleted upon flush. the flush here occurs as the
autoflush on the next query.
let me know if this makes sense. I agree that initially, I asked
myself, hmm should expunge count for Parent.collection.<deleted items>
also, or somehow revert that change? But looking from the perspective
of many-to-one, which is implicit in the one-to-many operations, it
seems like not.
--
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]
<mailto:[email protected]>.
To post to this group, send email to [email protected]
<mailto:[email protected]>.
Visit this group at https://groups.google.com/group/sqlalchemy.
For more options, visit https://groups.google.com/d/optout.
--
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 post to this group, send email to [email protected].
Visit this group at https://groups.google.com/group/sqlalchemy.
For more options, visit https://groups.google.com/d/optout.
