I believe that I may have found an error in dynamic relation backrefences.
When the dynamic query is executed, it appears to fetch all of the rows in
the referenced table instead of only the ones linked to the object from which
the dynamic relation was obtained. The following test script illustrates the
problem:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.orm.interfaces import MapperExtension
class Parent(object):
pass
class Child(object):
pass
meta = ThreadLocalMetaData()
Session = sessionmaker(autoflush=True, transactional=True)
session = None
class ThreadLocalSession(MapperExtension):
def get_session(self):
return session
parents_table = Table(
"parents", meta,
Column("id", Integer, Sequence("parents_id_seq"), primary_key=True),
Column("name", String(255), nullable=False))
mapper(Parent, parents_table)
children_table = Table(
"children", meta,
Column("id", Integer, Sequence("children_id_seq"), primary_key=True),
Column("name", String(255), nullable=False),
Column("parent_id", Integer, ForeignKey("parents.id"), nullable=False))
# The mapper extension is necessary, otherwise the dynamic query returned by
# Parent.children will not be associated with a session.
mapper(Child, children_table,
properties=dict(
parent=relation(Parent, backref=backref("children",
lazy="dynamic"))),
extension=ThreadLocalSession())
engine = create_engine("sqlite:///:memory:", echo=False)
meta.bind = engine
session = Session(bind=engine)
parents_table.create()
for name in ["parent1", "parent2"]:
parent = Parent()
parent.name = name
session.save(parent)
session.flush()
firstParent = session.query(Parent).get(1)
secondParent = session.query(Parent).get(2)
children_table.create()
for name in ["child1", "child2", "child3", "child4"]:
child = Child()
child.name = name
if name == "child1":
child.parent = firstParent
else:
child.parent = secondParent
session.save(child)
session.flush()
session.commit()
session.clear()
first_parent = session.query(Parent).get(1)
second_parent = session.query(Parent).get(2)
num_first_children = first_parent.children.count()
num_second_children = second_parent.children.count()
assert num_first_children == 1 and num_second_children == 3, \
"Children in first parent = %s, in second parent = %s" % \
(num_first_children, num_second_children)
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