In a treelike hierarchical data design, each node will have a parent ID,
referring to another node, except for the root node(s) which won't have a
parent. The trouble I'm having is that a parent ID refers to the primary ID of
another row in the same table. I don't know how to properly describe that
relation in sqlalchemy. Could anyone offer some advice?
Another problem is I'm trying to refer to all the posts with the same parent as
the kits of that parent post. I'd like it so the kits were lazy loaded and
accessible via parentobject.kits as a list. Is that how it's supposed to turn
out?
This is what isn't working, but best I can figure is how it should be done:
mapper.add_property('parent',relation(nodeclass,backref='kits',primaryjoin=nodeclass.c.id==nodeclass.c.parent))
You'll note my confusion in how is it supposed to tell which nodeclass key is
the foreign key, the id or the parent? I suppose it could ask the database
(which knows that the parent is the foreign key) but still, grokking this
eludes me. I end up with errors like the following:
File "/usr/lib/python2.4/site-packages/sqlalchemy/orm/properties.py", line
302, in _get_direction
if list(self.foreignkey)[0].primary_key:
IndexError: list index out of range
The above error only happens when I start trying to define the 'kits' relation
between nodes and ...nodes. But without defining the relation I am entirely
unable to do certain essential tasks like for instance:
for childNode in parentNode.kits:
childNode.DisplayStuff()
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