The following code raises a FlushError because the child object named
Cheshire is an orphan and the delete-orphan cascade rule is in effect.
It seems to me that an orphan which has no database identity should be
detached from its session, just as it was attached when appended to a
parent's list of children. Why does SA raise an exception instead?
from sqlalchemy import *
import sys
meta = BoundMetaData(sys.argv[1])
parentTable = Table("tether_parents",
meta,
Column("id", Integer,
Sequence("seq_tether_parents"), primary_key = True),
Column("name", String(10), nullable = False))
childTable = Table("tether_children",
meta,
Column("id", Integer,
Sequence("seq_tether_children"), primary_key = True),
Column("parent_id", Integer,
ForeignKey("tether_parents.id"), nullable = False),
Column("name", String(10), nullable = False))
class Child(object):
def __init__(self, name):
self.name = name
def __repr__(self):
return "Child(%s)" % repr(self.name)
class Parent(object):
def __init__(self, name):
self.name = name
children = []
def __repr__(self):
return "Parent(%s)" % repr(self.name)
mapper(Child, childTable)
mapper(Parent, parentTable, properties = dict(children =
relation(Child,cascade="all,delete-orphan")))
meta.drop_all()
meta.create_all()
meta.engine.echo = False
sess = create_session()
p = Parent("Carroll")
p.children = [Child("Alice"), Child("Dee"), Child("Dum")]
sess.save(p)
sess.flush()
sess.close()
sess = create_session(echo_uow = True)
p = sess.query(Parent).get_by_name("Carroll")
# New child.
p.children.append(Child("Cheshire"))
# Oops, changed my mind.
del p.children[3]
sess.flush()
sess.close()
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