Thanks, just what I needed.
-Jim
On 10/12/2010 9:38 AM, Conor wrote:
On 10/12/2010 09:20 AM, Jim Steil wrote:
Hi
Using SQLAlchemy 0.5.8.
I have the following model...
class Link(DeclarativeBase):
__tablename__ = 'link'
linkId = Column(Integer, autoincrement=True, primary_key=True)
name = Column(Unicode(50), nullable=False)
parentLinkId = Column(Integer, ForeignKey('link.linkId'))
url = Column(Unicode(255))
permissionId = Column(Integer,
ForeignKey('tg_permission.permission_id'))
description = Column(Text())
parentLink = relation(Link, primaryjoin=parentLinkId==Link.linkId)
permission = relation(Permission,
primaryjoin=permissionId==Permission.permission_id)
The problem is with the second to the last line. I'm trying to
create a relation to point to the parent link, which points back to
the same table. I'm using TurboGears and when I try to start my
server I get the following error:
parentLink = relation(Link, primaryjoin=parentLinkId==Link.linkId)
NameError: name 'Link' is not defined
I'm new to SA. Can someone help me out with this relation?
Due to Python semantics, "Link" is not bound to anything until the
class definition is complete. The get around this, SQLAlchemy provides
several options:
1. In this case, you can simply use parentLinkId==linkId as the
primaryjoin.
2. You can wrap the primaryjoin in a function/lambda, e.g.
primaryjoin=lambda: Link.parentLinkId==Link.LinkId. SQLAlchemy
will call this function sometime after the class definition is
complete, at which point "Link" is bound to something.
3. You can use a string as the primaryjoin, e.g.
primaryjoin="Link.parentLinkId==Link.linkId". SQLAlchemy will
evaluate this expression similar to option #2.
In any case, you need to include a remote_side argument to the
relation to indicate that this is the many-to-one side of the
relationship[1], e.g.
parentLink = relation(Link, primaryjoin=lambda: Link.parentLinkId==Link.linkId,
remote_side=lambda: [Link.linkId])
-Conor
[1]:
http://www.sqlalchemy.org/docs/orm/relationships.html?highlight=remote_side#adjacency-list-relationships
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