Question

I have a model Foo which have a ForeignKey to the User model.

Later, I need to grab all the User’s id and put then on a list

foos = Foo.objects.filter(...)  l = [ f.user.id for f in foos ] 

But when I do that, django grabs the whole User instance from the DB instead of giving me just the numeric user’s id, which exist in each Foo row.

How can I get all the ids without querying each user or using a select_related?

Thanks

Answer 1

Use queryset’s values() function, which will return a list of dictionaries containing name/value pairs for each attribute passed as parameters:

>>> Foo.objects.all().values('user__id') [{'user__id': 1}, {'user__id' 2}, {'user__id': 3}] 

The ORM will then be able to optimize the SQL query to only return the required fields, instead of doing a ‘SELECT *’.