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
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en.
