Question

I’m a Django newbie and I wonder if there is a more efficient way (at a database level) of doing the following.

I have the model:

class Foo(models.Model):
    item=models.IntegerField()
    another_item=models.IntegerField()

And want to get an iterable of all the distinct values of “item”.

This is what I have so far:

distinct=set([row.item for row in Foo.objects.all()])

This is easy to understand. But if I’m understanding how Django works then the SQL query is not very efficient because it is something like:

SELECT * FROM DB

when I only need:

SELECT DISTINCT item FROM DB

Any way of doing this more efficiently?

Answer 1

You want to use the distinct clause in combination with the values or values_list clauses.

Doc starts here. distinct, values and values_list are all in there.

So you could do:

Foo.objects.values_list('item', flat=True)

And that would return a list of item – matching your SELECT DISTINCT item FROM DB query.