Hi,
I've done something similar to this using annotation. It is a bad
nasty, but should work.
Firstly annotate all the MyModel instances with the max value of the
pk of the MyOtherModel:
qs = MyModel.objects.annotate(last_pk=Max('myothermodel__pk'))
Then filter these based on the myString:
qs = qs.filter(myothermodel__myString=certainStringValue)
Now get a values list of the last_pks:
pks = qs.values_list('last_pk', flat=True)
Finally select all myOtherModel instances based on these pks:
other_models = myOtherModel.object.filter(pk__in=last_pks).
This will only do one SQL query.
This should be fine until you've got loads of potential hits, where
the sub-select will be a beast, although Postgres is certainly OK
accepting lists of 1000s of pks to filter on.
As an aside you might want to consider following the python style
guide (http://www.python.org/dev/peps/pep-0008/) to make your code a
bit more readable.
Euan
I think what you want is:
MyModel.objects.filter
On Jun 11, 1:27 pm, Odd <[email protected]> wrote:
> I have these two rather simple models that looks something like this:
>
> class MyModel(models.Model):
> myName=models.CharField(max_length=60)
>
> class MyOtherModel(models.Model):
> myString=models.CharField(max_length=60)
> myModel=models.ForeignKey(MyModel)
>
> I will eventually have quite a number of MyOtherModelinstances. I have
> made a form where the users enters a string and a myModel instance,
> and it gets saved to the database. I need a query to get all the
> MyModel instances that has a certain stringvalue in myOtherModel, but
> only if it is the last entered one. My current solution is this:
>
> for i in mymodel.myothermodel_set.all():
>
> myOtherModel=MyOtherModel.objects.filter(myModel=i).order_by('-id')[:
> 1].get()
> if myOtherModel.myString==certainStringValue:
> objectsToRetur.append(i)
>
> This works, but I think it's not a very good. Is there maybe a better
> solution?
>
> Thanks!
>
> Odd-R.
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