On Aug 23, 2008, at 1:56 PM, Rob wrote:
>
> Hi,
>
> I'm using sqlalchemy 0.5 beta 3 and I am trying to have a Call object
> that contains two relations to a Contact object. One is the callee
> and the other is the caller. The code is as follows:
>
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy import Table, Column, Integer, String, MetaData,
> ForeignKey
> from sqlalchemy.orm import relation, backref, mapper
>
> Base = declarative_base()
> metadata = Base.metadata
>
> contact_table = Table('contact', metadata,
> Column('id', Integer, primary_key=True),
> Column('first_name', String(20)),
> Column('last_name', String(30)))
>
> call_table = Table('call', metadata,
> Column('id', Integer, primary_key=True),
> Column('subject', String(255)),
> Column('callee_id', Integer, ForeignKey('contact.id')),
> Column('caller_id', Integer, ForeignKey('contact.id')))
>
> class Contact(object):
> def __init__(self, first_name, last_name):
> self.first_name = first_name
> self.last_name = last_name
>
> def __repr__(self):
> return self.first_name + ' ' + self.last_name
>
> mapper(Contact, contact_table)
>
> class Call(object):
> def __init__(self, subject, callee, caller):
> self.subject = subject
> self.callee = callee
> self.caller = caller
>
> def __repr__(self):
> return self.subject
>
> mapper(Call, call_table, properties={
> 'callee':relation(Call,
> primaryjoin=call_table.c.callee_id==contact_table.c.id,
> backref='callee_calls'),
> 'caller':relation(Call,
> primaryjoin=call_table.c.caller_id==contact_table.c.id,
> backref='caller_calls')
> })
>
> c = Contact('my_first_name', 'my_last_name')
>
> I get a long error:
> sqlalchemy.exc.ArgumentError: Could not locate any equated, locally
> mapped column pairs for primaryjoin condition 'call.caller_id =
> contact.id' on relation Call.caller. For more relaxed rules on join
> conditions, the relation may be marked as viewonly=True.
>
"callee" and "caller" relate Call to another Call. The join condition
given does not connect "call_table" to itself and instead connects to
"contact_table" which is not involved in the relation(). Based on the
table it seems like "callee" and "caller" should relate to a Contact,
not a Call.
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