Juanjo Conti wrote:
> Hi all,
>
> I am worried about how to model the next scene (this is an example, but
> an appropriated one): In the model we have People, and there are
> different kind of people, let's say: Professors, Students and Other.
> Each People object has a 'type' attribute. Type can be P, S or O.
>
> So far, all right.
>
> Each people has an identifier that looks like: {LETTER}{NUMBER}. P1, P2,
> P3 and S1 are examples of valid identifiers.
>
> When you instance a People object you know its type but not its number:
>
> p = People(type="S")
>
> The question is, how can I handle this numbers in my model? The count
> should be dependent of the type.
>
> I am thinking about creating PostgreSQL sequences and use them to
> retrieve the propitiated number each time a People is instanced:
>
> ...
> if type == "S":
> self.number = seq_wrapper_s.next()
> elif typ == "P":
> self.number = seq_wrapper_p.next()
> else:
> self.number = seq_wrapper_o.next()
> ...
>
> But this will tie me to an specific data base engine. Is there a way of
> doing this task in Django in a independent-db-engine way?
>
>
Is there a strong reason why the count should depend on the type? Can't
you have a more standard model with two fields - 'id' (which would be a
normal auto-increment primary key field) and 'type' (which could be 'P',
'S', or 'O', or else you could model it as a SmallIntegerField, with a
set of valid choices)?
e.g.
PERSON_TYPE_CHOICES=((1,'Professor'),(2,'Student'),(3,'Other'))
class Person(models.Model)
# (no need to put in the id field explicitly as it will be generated
by django.)
type=models.SmallIntegerField(choices=PERSON_TYPE_CHOICES)
... any other person fields.
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