is this joined inheritance or concrete?
IMO if Product inherits Node, they has to have same PK?
On Thursday 12 February 2009 23:56:12 Bruce van der Kooij wrote:
> Many thanks Michael, your instructions were spot-on. In the process
> of following your instructions I decided to switch from using
> ext.declarative to a non-declarative style (define tables, define
> Python objects, setting up the mapping, the works :-).
>
> Regretfully while trying to work out the rest of the model (see
> ASCII diagram below) I hit another wall. I'm currently trying to
> make the model Product inherit from Node, I'm having issues with
> this because the situation I'm faced with deviates from the
> excellent examples in the documentation.
>
> +--------------+ +--------------+
>
> | Node | | User |
>
> +--------------+ 1 +--------------+
>
> | nid (PK, AI) | /--->| uid (PK, AI) |
> | vid | 0..* / +--------------+
> | uid |------/
>
> +--------------+
> ^
>
> | is subclass of
>
> +-------------+
>
> | Product |
>
> +-------------+
>
> | vid (PK) |
> | nid |
>
> +-------------+
>
> The User relation is irrelevant, but I added it to present "the
> full picture". I also excluded the relation with the NodeRevision
> model since I already posted that above.
>
> Creating a Product instance, adding it to the session and
> committing it results in a node, a revision and a product. However
> the problem that arises is that the row for the Product table will
> not have the correct vid (it will remain on the default value, not
> with the vid of the NodeRevision associated with the Node).
> Subsequent INSERTS will then fail (duplicate entry). I'm led to
> believe that the problem stems from the fact that the primary key
> for the products table differs from that of the node table (vid
> compared to nid).
>
> I haven't yet managed to figure out a solution to this predicament,
> I'll probably look into multi-table mapping next to see if that
> might help.
>
> Here's what I've managed to get so far:
>
> # tables.py:
> node_table = Table("node", metadata,
> Column("vid", Integer, ForeignKey("node_revisions.vid")),
> Column("uid", Integer, ForeignKey("users.uid")),
> autoload=True
> )
>
> node_revisions_table = Table("node_revisions", metadata,
> Column("nid", Integer, ForeignKey("node.nid")),
> Column("uid", Integer, ForeignKey("users.uid")),
> autoload=True
> )
>
> uc_products_table = Table("uc_products", metadata,
> Column("vid", Integer, ForeignKey("node_revisions.vid"),
> primary_key=True),
> Column("nid", Integer, ForeignKey("node.nid")),
> autoload=True
> )
>
> # models.py (simplified):
> class Node(object):
> pass
>
> class NodeRevision(object):
> pass
>
> class Product(Node):
> pass
>
> # database.py (mapping):
> node_mapper = mapper(Node, node_table,
> polymorphic_on=node_table.c.type,
> properties={
> "user": relation(User),
> "latest_revision": relation(NodeRevision,
> primaryjoin=node_table.c.vid ==
> node_revisions_table.c.vid,
> post_update=True
> ),
> "revisions": relation(NodeRevision,
> primaryjoin=node_table.c.nid ==
> node_revisions_table.c.nid,
> backref=backref("node",
> primaryjoin=node_revisions_table.c.nid ==
> node_table.c.nid
> )
> )
> }
> )
>
> node_revision_mapper = mapper(NodeRevision, node_revisions_table,
> properties={
> "user": relation(User)
> })
>
> uc_products_mapper = mapper(Product, uc_products_table,
> polymorphic_identity="product"
> )
>
> # Example of creating a product (user relation left out for
> simplicity):
> product = Product().
> product.latest_revision = NodeRevision(node=product)
>
> Thanks for all your help.
>
> Best regards,
>
> Bruce
>
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