On May 14, 3:29 pm, Jani Tiainen <rede...@gmail.com> wrote:
> 14.5.2012 14:50, akaariai kirjoitti:
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> > On May 14, 2:37 pm, Jani Tiainen<rede...@gmail.com> wrote:
> >> Hi,
>
> >> I have in my database quite a bunch of a models where I do have quite
> >> large fields and I'm using .only('pk', 'identifier') to fetch only those
> >> two fields - mainly to make serverside natural sort for a data. Database
> >> is legacy one and it's being used with other external programs as well
> >> so changing it is not possible.
>
> >> After sorting I just need to get slice of data and fetch rest of fields
> >> in one query. I haven't found simple way to fetch rest of the fields in
> >> one request.
>
> >> So what I would like to do:
>
> >> qs = MyModel.objects.all().only('pk', 'identifier')
>
> >> list_of_models = sort_naturally(qs, 'identifier')
>
> >> sublist_of_models = list_of_models[10:20]
>
> >> for model in sublist_of_models:
> >> model.fetch_all_deferred_fields()
> > While not totally same, how about:
> > for model in MyModel.objects.all(pk__in=[obj.pk for obj in
> > sublist_of_models]):
> > or maybe this will work, too:
> > for model in MyModel.objects.all(pk__in=sublist_of_models):
>
> > You will lose the sorting, so you will need to resort the models
> > again. If your model instances are changed, you will lose those
> > changes.
>
> > If the above isn't enough the best you can do currently is to create a
> > helper method which will do the merge manually.
>
> That would probably do, and now you mentioned it I already have merge
> function that can merge arbitrary dicts to models... ;)
>
> "Dare to be stupid" like Weird Al Yankovic sings...
>
> Of course my DB backend Oracle has limit of (I think it was 1000)
> elements in parameter list so it would require additional work if
> someone wants to work with more than 1k elements in a sublist.
I don't know the version of Django you are using, but at least 1.4
should automatically know how to split the list into multiple parts to
work around the 1000 parameters limit in Oracle. See:
https://github.com/django/django/blob/stable/1.4.x/django/db/models/sql/where.py#L181
- Anssi
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