Django

Django QuerySet - only() vs defer() vs exclude()

If you have some fields in your Django model that contain a lot of data and you don't need those fields for a particular query, you can tell Django not to retrieve them with defer():

Event.objects.defer("description")

While defer() works at the attribute level, exclude() works on the row level.

In other words, exclude() arguments are used after the WHERE clause -- i.e., SELECT * FROM users WHERE name = 'jan' -- while defer() changes * to the provided fields -- i.e., SELECT name, email FROM users.

Opposite to defer() is only(). If you have fewer fields that you want to retrieve than those you don't, you can use only() to retrieve only the fields provided as arguments:

Event.objects.only("title")