Hi all,
I'm trying to make something similar to Michael's polymorphism
sample (from his blog) work, but I'm finding that SQLAlchemy isn't
respecting the ordering restrictions imposed by the ForeignKey()
constraints on my tables. Here are the table definitions:
sec_principals = Table('sec_principals', db,
Column('principal_id', Integer,
primary_key=True),
Column('name', String(64), nullable=False),
mysql_engine='InnoDB')
sec_users = Table('sec_users', db,
Column('user_id', Integer,
ForeignKey('sec_principals.principal_id'),
primary_key=True),
Column('first_name', String(32), nullable=False),
Column('last_name', String(32), nullable=False),
Column('email_address', String(64), nullable=False),
Column('password', String(48), nullable=False),
mysql_engine='InnoDB')
sec_groups = Table('sec_groups', db,
Column('group_id', Integer,
ForeignKey('sec_principals.principal_id'),
primary_key=True),
Column('description', String(64)),
mysql_engine='InnoDB')
sec_group_members = Table('sec_group_members', db,
Column('group_id', Integer,
ForeignKey('sec_groups.group_id'),
nullable=False),
Column('member_id', Integer,
ForeignKey
('sec_principals.principal_id'),
nullable=False),
mysql_engine='InnoDB')
and the problem I'm seeing is that when I do
u = User(name='alastair', ...)
g = Group(name='Users', ...)
g.members.append(u)
objectstore.commit()
SQLAlchemy keeps trying to insert into sec_group_members before it
has inserted the user record in sec_users. Obviously this will
fail because the user doesn't have an ID until it's been inserted.
Surely this should work without requiring an additional
objectstore.commit()? Or am I doing something wrong here?
(I should also perhaps note that, bizarrely, this behaviour only
seems to occur when Python has generated .pyc files for the package
containing the tables and mapping definitions...)
In case it matters, my mappers look like this:
principal_join = select(
[sec_principals,
sec_users.c.first_name,
sec_users.c.last_name,
sec_users.c.email_address,
sec_users.c.password,
column("'user'").label('type')],
sec_principals.c.principal_id==sec_users.c.user_id).union_all(
select(
[sec_principals,
sec_groups.c.description,
column("'group'").label('type')],
sec_principals.c.principal_id==sec_groups.c.group_id)).alias
('pjoin')
class PrincipalLoader(MapperExtension):
def create_instance(self, mapper, row, imap, class_):
if row['pjoin_type'] == 'user':
return User()
elif row['pjoin_type'] == 'group':
return Group()
else:
return Principal()
principalLoaderExtension = PrincipalLoader()
assign_mapper(Principal, sec_principals)
Principal.dumb_mapper = Principal.mapper
Principal.mapper = mapper(Principal,
principal_join,
extension=principalLoaderExtension)
assign_mapper(User, sec_users, inherits=Principal.dumb_mapper)
assign_mapper(Group, sec_groups, inherits=Principal.dumb_mapper)
Principal.dumb_mapper.add_property('groups',
relation(Group.mapper,
sec_group_members,
backref='members'))
Group.mapper.add_property('members',
relation(Principal.mapper,
sec_group_members,
backref='groups'))
Principal.mapper.add_property('groups',
relation(Group.mapper,
sec_group_members,
backref='members'))
I'm using the latest SQLAlchemy from Subversion (i.e. revision
1234), in case that's relevant.
Kind regards,
Alastair.
--
http://www.alastairs-place.net
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