6. How to select some fields only in a queryset?ΒΆ

_images/usertable.png

The auth_user model has a number of fields in it. But sometimes, you do not need to use all the fields. In such situations, we can query only desired fields.

Django provides two ways to do this

  • values and values_list methods on queryset.
  • only_method

Say, we want to get first_name and last_name of all the users whose name starts with R. You do not want the fetch the other fields to reduce the work the DB has to do.

>>> User.objects.filter(
    first_name__startswith='R'
).values('first_name', 'last_name')
<QuerySet [{'first_name': 'Ricky', 'last_name': 'Dayal'}, {'first_name': 'Ritesh', 'last_name': 'Deshmukh'}, {'first_name': 'Radha', 'last_name': 'George'}, {'first_name': 'Raghu', 'last_name': 'Khan'}, {'first_name': 'Rishabh', 'last_name': 'Deol'}]

You can verify the generated sql using str(queryset.query), which gives.

SELECT "auth_user"."first_name", "auth_user"."last_name"
FROM "auth_user" WHERE "auth_user"."first_name"::text LIKE R%

The output will be list of dictionaries.

Alternatively, you can do

>> queryset = User.objects.filter(
    first_name__startswith='R'
).only("first_name", "last_name")

str(queryset.query), gives us

SELECT "auth_user"."id", "auth_user"."first_name", "auth_user"."last_name"
FROM "auth_user" WHERE "auth_user"."first_name"::text LIKE R%

The only difference between only and values is only also fetches the id.