Hi Neil!
I'm also not sure if what I think to be correct is right. In the
example I provided you are right but take notice that it's a
bidirectional relationship. What if it was two unidirectional
relationships?
A->B
B->A
A1 -> {B1, B2, B3}
B1 -> {A2, A3}
I think this would require two intermediate tables (or only one table
with a "direction" column).
Is my reasoning correct?
Thanks,
Miguel Tavares
2009/8/12 Neil Muller <drnlmuller+sqlobj...@gmail.com>:
> On Wed, Aug 12, 2009 at 12:36 PM, Miguel Tavares<migtava...@gmail.com> wrote:
>> Hi Oleg!
>>
>> A second intermediate table can be used to state a second many-to-many
>> relationship and it might make more sense to have it in reverse
>> order.
>>
>> Imagine this scenario:
>>
>> class Address(SQLObject):
>> Address = sqlobject.StringCol ()
>> People = sqlobject.RelatedJoin ('Person')
>>
>> class Person(SQLObject):
>> Name = sqlobject.StringCol ()
>> Addresses = sqlobject.RelatedJoin ('Address')
>>
>> So a Person can have several addresses (House, Work, Beach House, etc)
>> and each Address can be for several Persons (all the member of the
>> family for example).
>>
>> Does this makes any sense?
>
> With this example, you'll create an intermediate table which looks
> something like:
>
> id1 : idPerson1 : idAddress1
> id2 : idPerson1 : idAddress2
> id3 : idPerson2 : idAddress1
> id4 : idPerson2 : idAddress3
> etc.
>
> where idPerson & idAddress are the identifiers for the respective
> entries in the Person and Address tables [1].
>
> This captures the entire relationship - selecting entries based on the
> address will give you all the Person records, and selecting on the
> Person will give you all the address records.
>
> I'm not seeing why you think you need multiple intermediate tables?
>
> [1] I've swapped the order of the two columns from how sqlobject will
> actually create the table, but that doesn't really matter.
>
> --
> Neil Muller
> drnlmul...@gmail.com
>
> I've got a gmail account. Why haven't I become cool?
>
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