On Thu, Oct 8, 2009 at 9:06 AM, mdipierro <mdipie...@cs.depaul.edu> wrote:
>
> On a second thought.... why is this not supported?
>
> Because I am not convinced this is a good idea.
>
> If every record of table A only references one record of table B and
> vice versa then perhaps there should be only one table AB.
>
> If this is a one (A) to many (B) relation then A cannot contain a
> reference to B because would not be unique.
>
> If this is a many to many then there should be a link table. In your
> case:
>
> db.define_table('ports',
> Field('name','string')
> )
> db.define_table('agents',
> field('name','string')
> )
> db.define_table('port_agents',
> Field('port_id', db.ports),
> Field('agent_id',db.agents)
> )
>
Using your own statement:
I have port_agents, which are assigned to specific ports. One port
might have several port_agents.
At the same time each port might have a preferred agent,
I think it is reasonable to assume that an agent may move between ports
(even if only on rare occaision), so Massimo's example tables are - I think
- good. The only missing thing is somthing for your last statement, and
you will want to think about what makes more sense - is this an attribute of
the port, or is this an attribute of the port_agents relationship. I would
probably go for the latter, and add an attribute for "preferred" pairing,
but then you would have the possibility of many "preferred"s, so adding a
Field('preferred_agent_id', db.agents) to ports might be the way you will
prefer (as it will limit you to a one-to-many relationship at worst).
Yarko
> It is also possible that I do not understand the problem you are
> working on and I am completely wrong.
>
> Massimo
>
>
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