On Feb 12, 2008, at 9:41 AM, Donovan Kolbly wrote:
>
> I am trying to go through the mapping tutorial in 0.4.2p3 for
> association objects. I get an error about "Could not assemble any
> primary key columns for mapped table 'association'" when attempting to
> map the association table itself. This is straight out of the Mapping
> Configuration docs that comes with the distribution...
>
> Any thoughts on where things are going awry?
>
> Here's my complete code:
>
> from sqlalchemy import create_engine, \
> Table, Column, Integer, String, \
> MetaData, ForeignKey
> from sqlalchemy.orm import relation, sessionmaker, mapper
>
> engine = create_engine('sqlite:///:memory:', echo=True)
>
> metadata = MetaData();
>
> left_table = Table('left', metadata,
> Column('id', Integer, primary_key=True))
>
> right_table = Table('right', metadata,
> Column('id', Integer, primary_key=True))
>
> association_table = Table('association', metadata,
> Column('left_id', Integer, ForeignKey('left.id')),
> Column('right_id', Integer, ForeignKey('right.id')),
> Column('data', String(50))
> )
>
> class Parent(object): pass
> class Association(object): pass
> class Child(object): pass
>
> mapper( Parent, left_table, properties={
> 'children':relation(Association)
> })
>
> mapper( Association, association_table, properties={
> 'child':relation(Child) # <--- chokes here
> })
>
> mapper( Child, right_table)
>
> metadata.create_all( engine )
>
the association_table itself has no primary key columns, so you have
to tell the mapper which columns it should consider to be the primary
key:
mapper(Association, association_table, properties={...},
primary_key=[association_table.c.left_id, association_table.c.right_id])
Ill update the docs right now.
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