On Thu, Mar 4, 2010 at 2:31 PM, Daniel Robbins <drobb...@funtoo.org> wrote:
> Hi All,
>
> I have created a base declarative object that has a pre-made primary
> key, so I don't have to add it to all my child tables:
I figured out how to do this, using the following code:
seqnum=0
def PrimaryKey(seqprefix=None):
global seqnum
if not seqprefix:
seqnum += 1
seqname = "id_seq_%s" % seqnum
else:
seqname = "%s_id_seq" % seqprefix
return Column(Integer, Sequence(seqname, optional=True),
primary_key=True)
class ClassDefaults(DeclarativeMeta):
def __init__(cls,classname, bases, dict_):
if not ( dict_.has_key('__mapper_args__') and
dict_['__mapper_args__'].has_key('polymorphic_identity') ):
# Only add the key if we are not creating a
polymorphic SQLAlchemy object, because SQLAlchemy
# does not want a separate 'id' key added in that case.
# seqprefix can be None
seqprefix = getattr(cls,'__tablename__',None)
dict_['id'] = PrimaryKey(seqprefix=seqprefix)
return DeclarativeMeta.__init__(cls, classname, bases, dict_)
Base = declarative_base(metaclass=ClassDefaults)
class Location(Base):
__tablename__ = 'location'
parent_id = Column(Integer, ForeignKey('location.id'))
parent = relation('Location', backref=backref('children'),
remote_side='location.c.id')
name = UniqueString(25)
desc = Column(String(80))
This code above allows my adjacency list table Location to be handled
correctly, and also allows my Single Table inheritance (not included
in the above code) to work too. The PrimaryKey() function will
generate numerically increasing sequence names with no argument, or a
specific sequence name if supplied with an argument. ClassDefaults
calls it with the __tablename__ if one is available to create a
sequence that has a name similar to the underlying table (with a
"_seq" suffix.)
Regards,
Daniel
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