On Aug 20, 2012, at 7:08 PM, adolfo wrote:
> Thanks Michael.
>
> The question is: how can I use that trick as a relation?
>
> I can do:
>
> session.query(Node).outerjoin(Node.right_nodes)
>
> and
>
> session.query(Node).outerjoin(Node.left_nodes)
>
> but not
>
> session.query(Node).outerjoin(Node.all_nodes)
>
> and that is what I'm looking for. I mean the relation() functionality.
>
> Is there some way to accomplish that?
the outerjoin is like this:
subq = select([node_to_node.c.left_node_id.label('parent'),
node_to_node.c.right_node_id.label('child')]).union(select([node_to_node.c.right_node_id,
node_to_node.c.left_node_id]))
nalias = aliased(Node)
session.query(Node).outerjoin(subq, Node.id==subq.c.parent).outerjoin(nalias,
nalias.c.id==subq.c.child)
that is, a UNION in the middle.
you can make a relationship() where you take that subq above and make it the
"secondary" part of the relationship, if you wanted to have more of the
relationship mechanics available.
>
>
> Thanks again!
>
> Adolfo
>
> On Monday, August 20, 2012 5:35:51 PM UTC-5, Michael Bayer wrote:
>
> On Aug 20, 2012, at 6:07 PM, adolfo wrote:
>
>> I have a Self-Referential Many-to-Many Relationship situation where the
>>
>> right_nodes = relationship("Node",
>> secondary=node_to_node,
>> primaryjoin=id==node_to_node.c.left_node_id,
>> secondaryjoin=id==node_to_node.c.right_node_id,
>> backref="left_nodes"
>>
>> works fine.
>> The problem:
>> I need a "related nodes" relationship, which, in one expression, returns all
>> related nodes, both left nodes and right nodes, excluding the given node
>> itself.
>> Is that possible using the RELATIONSHIP construct?
>
> this is the "my friends and people who I'm friends with" query and the recipe
> is....well I guess I didn't put it up anywhere yet, the idea is to use a
> @property:
>
> class MyClass(Base):
> # ...
>
> @property
> def all_nodes(self):
> return self.left_nodes + self.right_nodes
>
> to do this in SQL only requires a UNION in a subquery. If you really wanted
> that I can work it out, it's more burdensome but if you have a specific query
> style in mind it could be useful.
>
>
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