Re: Models relationship

On Thu, 23 Aug 2012 05:20:38 -0700 (PDT), Fernando Andreacci
<fandreacci@gmail.com> declaimed the following in
gmane.comp.python.django.user:

> Hello,
>
> I'm a new Django user, and I have the following question:
>
> I have one Model called *factory, *with several fields like (name, address,
> phone, etc).
>
> Each factory can be a customer, a supplier or both.

I presume a "factory" can be a customer of more than one other
"factory"s, same for "supplier" -- otherwise you're defining a self-link
back to the same table.

Instead you are probably looking at one many-to-many table in which
both sides of the relationship are the same table. You probably need to
implement business logic to ensure that customer<>supplier.

In pseudo-SQL, this would be something like:

create table Factories
(
ID integer autoincrement primary key,
name varchar(?) not null,
address1 varchar(?) not null,
address2 varchar(?) null,
city varchar(?) not null,
state varchar(?) not null,
postcode char(10),
phone char(10)
)

create table Supplies
(
ID integer autoincrement primary key,
Supplier integer not null foreign key Factories(ID) on delete
cascade,
Customer integer not null foreign key Factories(ID) on delete
cascade
)

In Django -- Supplies would probably be an explicit "through" table;
or just managed separately.
--
Wulfraed Dennis Lee Bieber AF6VN
wlfraed@ix.netcom.com HTTP://wlfraed.home.netcom.com/

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