Well, you could specify the primaryjoin as described here:
http://www.sqlalchemy.org/docs/adv_datamapping.myt#advdatamapping_properties_customjoin
but I suspect that your existing mapper will Just Work if you switch
to a composite FK, rather than 3 keys on individual columns
t_bovines = Table( 'bovines', metadata,
Column('id', Integer, primary_key=True),
Column('entrydate', Integer),
Column('key1', Integer),
Column('key2', Integer),
Column('key3', String),
Column('var', Integer),
Column('val', Integer),
ForeignKeyConstraint(['key1', 'key2', 'key3'],
['enterprise.key1', 'enterprise.key2', 'enterprise.key3'])
)
t_entreprises = Table( 'entreprises', metadata,
Column('key1', Integer),
Column('key2', Integer),
Column('key3', String),
Column('lname', Unicode(30)),
Column('fname', Unicode(30)),
Column('street', Unicode(30)),
Column('country', String(1)),
Column('zip', String(5)),
Column('locality', Unicode(30)),
PrimaryKeyConstraint('key1', 'key2', 'key3')
)
# similarly adjust surfaces
On 1/9/07, exhuma.twn <[EMAIL PROTECTED]> wrote:
>
> Hi,
>
> I have to load a table from 2 different data-sources witch each having
> 3 different primary keys. This is because those 2 datasources are
> already exported from 3 databases from an archaic application.
>
> >From those 2 datasources I created - after normalising - 3 new tables.
> The main table keeps the 3 primary keys as one composite primary key.
> The two other tables have those 3 fields as foreign keys. Now, if I map
> those table definitions onto a table with relations, sqlalchemy
> complains with the following error:
>
> """
> sqlalchemy.exceptions.ArgumentError: Error determining primary and/or
> secondary join for relationship 'bovines' between mappers
> 'Mapper|Enterprise|entreprises' and 'Mapper|Bovine|bovines'. You
> should specify the 'primaryjoin' (and 'secondaryjoin', if there is an
> association table present) keyword arguments to the relation() function
> (or for backrefs, by specifying the backref using the backref()
> function with keyword arguments) to explicitly specify the join
> conditions. Nested error is "Cant determine join between 'entreprises'
> and 'bovines'; tables have more than one foreign key constraint
> relationship between them. Please specify the 'onclause' of this join
> explicitly."
> """
>
> Ok, so I have to specify the "onclause". But how do I do that? For
> reference, here is the (non-working) data definition:
>
> t_bovines = Table( 'bovines', metadata,
> Column('id', Integer, primary_key=True),
> Column('entrydate', Integer),
> Column('key1', Integer, ForeignKey('entreprises.key1')),
> Column('key2', Integer, ForeignKey('entreprises.key2')),
> Column('key3', String, ForeignKey('entreprises.key3')),
> Column('var', Integer),
> Column('val', Integer),
> )
>
> t_entreprises = Table( 'entreprises', metadata,
> Column('key1', Integer, primary_key=True),
> Column('key2', Integer, primary_key=True, default=0),
> Column('key3', String, primary_key=True),
> Column('lname', Unicode(30)),
> Column('fname', Unicode(30)),
> Column('street', Unicode(30)),
> Column('country', String(1)),
> Column('zip', String(5)),
> Column('locality', Unicode(30)),
> )
>
> t_surfaces = Table( 'surfaces', metadata,
> Column('id', Integer, primary_key=True),
> Column('entrydate', Integer),
> Column('key1', Integer, ForeignKey('entreprises.key1')),
> Column('key2', Integer, ForeignKey('entreprises.key2')),
> Column('key3', String, ForeignKey('entreprises.key3')),
> Column('var', Integer),
> Column('val', Integer),
> )
>
> metadata.create_all()
>
> class Bovine(object):
> pass
>
> class Surface(object):
> pass
>
> class Enterprise(object):
> def __repr__(self):
> return "[Entreprise %s %s %s]" % (self.key1, self.key2,
> self.key3)
>
> usermapper = mapper(Bovine, t_bovines)
> usermapper = mapper(Surface, t_surfaces)
> usermapper = mapper(Enterprise, t_entreprises, properties={
> 'bovines': relation(Bovine),
> 'surfaces': relation(Surface)
> })
>
>
> >
>
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