django database efficient querysets on two models

Question

I am quite new to django - and I was wondering if I could use the ORM to make the below queries more efficiently:

# somewhere in views.py..
if slug is not None:
    slug_field = self.get_slug_field()
    pkid = FinalModel.objects.all().get(slug__exact=slug)
    queryset = queryset.filter(owner__exact=pkid.id)
    obj = queryset.get()
    return obj

So, basically, what I am doing is (to return an object), first: get the pkid using the slug in the url, then use this info (pkid.id) to get the correct full object using the queryset (which operates on a different model - which is OnetToOne keyed to the FinalModel) statement above.

So, in a nutshell, I am first extracting the PK using the slug (Model=FinalModel) and use this PK on another model (the queryset model) which is OneToOne keyed to the FinalModel (using the owner attribute).

I am not sure that using two such statements is efficient for the DB (I am no expert on this either) - and I was wondering if anyone could suggest how I could combine the two statements (pkid and queryset) to get the final object more efficiently.

Sorry if this is a django 101 question.

Daniel Roseman · Accepted Answer · 2013-11-17 14:31:52Z

1

This would have been easier to answer if you'd shown your models. But assuming owner is a ForeignKey from FinalModel to whatever model you want to get at the end, you can use the double-underscore syntax to do a JOIN:

obj = MyModel.objects.get(owner__slug=slug)

(Note you don't need to specify exact, it's the default.)

answered Nov 17, 2013 at 14:31

Daniel Roseman

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3 Comments

JohnJ Over a year ago

Thanks so much for this - that works perfectly!! I was wondering if I could ask you another question (probably not completely related to this). I was wondering what this statement does: queryset = queryset.filter(**{slug_field: slug}) especially, what does **{slug_field: slug} construct mean here? Thanks so much for all your help - has certainly helped me understand better.

Daniel Roseman Over a year ago

**dict is just a means of passing a dictionary as keyword arguments. That's useful because the keyword name itself can be a variable, as in your example, as well as the value.

JohnJ Over a year ago

Thanks a tonne. Solved all problems :) Marked your answer as correct!

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