On May 22, 11:28 am, akaariai <akaar...@gmail.com> wrote:
> Hi all,
>
> I am trying to find a best way to solve the following problem:
>
> I have chemicals, each of which has a list of codes and names.
> Chemicals have too many codes and names to put directly into the
> Chemical model.
>
> Example (pseudo) models.py:
>
> class Chemical():
> pass
>
> class Name():
> chemical = ForeignKey(Chemical)
> nametype = Integer # in reality a foreign key
> name = varchar(50)
> unique_together(chemical, nametype)
>
> class Code():
> chemical = ForeignKey(Chemical)
> codetype = Integer
> code = varchar(50)
> unique_together(chemical, codetype)
>
> I need to make listings of these chemicals, (chemical_id, name, code),
> and I need to change dynamically which name and which code to show.
> Naturally the listings need to be searchable.
>
> The most beautiful solution would be the possibility to directly use:
>
> Chemical.objects.filter(code__codetype = 1).filter(name__nametype =
> 1)\
> .filter(code__code__contains = '123').values
> ('pk','code__code', 'name__name')
>
> but Django orm can't handle this currently. I actually looked into the
> code to see how hard this would be to implement for values and
> values_list. I quickly saw that this is not something you want to do
> as your first Django coding project...
>
> So far I have a few solutions to this problem.
>
> 1) Use raw sql
> - works, but is ugly
>
> 2) Create a database view and a corresponding model, and use that for
> listings
> - works, but is after all only marginally better than solution 1.
> Biggest problem is that it is not DRY.
>
> 3) Filter both Name and Code manually, then join them in python.
> - I haven't really tried this one. I think this is the ugliest so
> far.
>
> I am currently using solution 2. but I am wondering if there is some
> better way to do this? Maybe using .extra() in some way?
>
> By the way, I have just switched to Django from JDBC + jsp. I can't
> believe how easy web programming can be with the right tools. Thank
> you!
If the problem is just the values_list call, you could easily get the
values into a list yourself using your existing query:
chemicals = Chemical.objects.filter(
code__codetype=1, name__nametype=1,
code__code__contains = '123'
).select_related()
values = [(c.pk, c.code.code, c.name.name) for c in chemicals]
There's a slight overhead here in instatiating all the chemical
objects, but it's not significant. You will need select_related, as
I've shown above, to avoid making multiple queries though.
--
DR.
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