On Nov 23, 2011, at 5:20 AM, Enrico Morelli wrote:
> On Wed, 23 Nov 2011 10:59:03 +0100
> Enrico Morelli <more...@cerm.unifi.it> wrote:
>
>
>> These are the mappers:
>> mapper(Ligand, ligand_table,
>> properties={
>> 'ligand':relationship(LigandLigand,
>> primaryjoin=and_(ligand_table.c.id==ligand_ligand_table.c.ligand_id1,
>> ligand_table.c.id==ligand_ligand_table.c.ligand_id2),
>> backref=backref('ligandligand') ), })
>>
>> mapper(LigandLigand, ligand_ligand_table,
>> properties={
>> 'first_sphere': relationship(Ligand,
>>
>> primaryjoin=and_(ligand_ligand_table.c.ligand_id2==ligand_table.c.id,
>>
>> ligand_ligand_table.c.ligand_id1==ligand_table.c.id),
>> backref=backref('root')),
>> })
>>
>> When I try to access to the ligand.ligand properties, this is empty
>> even if in the db there are relations. Where is the problem?
>>
>> Thanks
>>
>>
>
> I think to have solved the problem changing the logical operator in the
> primaryjoin from and_ to or_.
>
> Now when I remove the relations I have the following warning:
> SAWarning: Multiple rows returned with uselist=False for lazily-loaded
> attribute
> LigandLigand.ligandligand' value = callable_(passive=passive)
it means a relationship is expecting many-to-one or one-to-one and getting more
than one row back. Setting uselist=True on that backref would resolve this
issue, though if you only intend for one row to come back there you might want
to triple-check what SQL is being emitted. The configuration here is already
outside the normal realm of a "relationship" between two tables (not a
traditional foreign key to primary key) so you may have to change or forego the
usage of relationship() here. If it were me I'd just use two relationships
to represent "ligand1" and "ligand2".
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