Here's a MVCE-style example showing the problem I have:
from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import *
Base = declarative_base()
class Type(Base):
__tablename__ = 'types'
id = Column(Integer, primary_key=True)
def __repr__(self):
return '<Type {}>'.format(self.id)
class Bar(Base):
__tablename__ = 'bars'
id = Column(Integer, primary_key=True)
deleted = Column(Boolean, nullable=False, default=False)
type_id = Column(ForeignKey('types.id'), nullable=True)
type = relationship(Type, backref=backref('bars', primaryjoin='(Bar.type_id
== Type.id) & ~Bar.deleted'))
def __repr__(self):
return '<Bar {} [{}, {}]>'.format(self.id, self.type, self.deleted)
e = create_engine('postgresql:///test', echo=False)
Base.metadata.create_all(e)
s = Session(e, autoflush=False)
t = Type()
b1 = Bar(type=t)
b2 = Bar(type=t, deleted=True)
s.add(t)
s.commit()
s.delete(t)
s.flush()
So basically when I'm using the relationship in my code I never want
deleted items to show up. However, for cascading I still need them.
Using serverside cascades could work but if there's a way of doing that
without having to switch to serverside cascades it'd be nicer.
BTW the example doesn't work with SQLite, apparently it automatically NULLs
invalid FKs even without specifying `on delete set null` on the FK.
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The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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