On Aug 22, 2007, at 8:27 AM, Christoph Haas wrote:
>
> But that example deals with User and Address tables and not with
> self-references. I suspect I have to alias the table. Roughly I'm
> thinking of something like:
>
> properties={
> 'ptr_records': relation(Record, primaryjoin=and_(
> records_table.c.type=='PTR',
> records_table.c.inet=records_table2.c.inet
> ))
> }
>
> I don't know how to say "match other Record objects where the 'inet'
> column contains the same value". How do I do that correctly?
Well the issue here is that while its a self-referential relationship
you're dealing with, its not an "adjacency list" model, which is
really what our "self-referential" relation() is designed to do.
Normally you can use the "remote_side" attribute to indicate
whichever column on the join condition is "remote", but here its the
same column.
Doing the alias thing is possibly a solution. it would look like this:
records2 = records.alias()
rmapper = mapper(Record, records2, non_primary=True)
'ptr_records':relation(rmapper, primaryjoin=and_(
records2.c.type=='PTR', records.c.inet=records2.c.inet),
viewonly=True)
)
the above should work in theory but I havent tried it. notice that
the records2 alias indicates the "child" side of the relationship so
its the one which gets the "PTR" criterion. "viewonly=True" is to
eliminate whatever issues arise in calculating the persistence aspect
of the relation since you only need loading here.
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