Django Query Expressions: F()
The F() Django query expression allows performing a database operation on a
field without loading its value in memory. Using it, we can update values
for not only a particular object but also for an entire queryset.
To do that, we need to use F() in conjunction with the
update() method.
Following is an example from the Django documentation:
Reporter.objects.all().update(stories_filed=F('stories_filed') + 1)
The F() expressions helps improving performance by reducing the number of
database queries generated as well as by offloading the processing chore to the database.
I got to learn about F() expressions when I needed to provide an alias to a
database field in
openwisp-controller.
Not only this, F() expressions can also be used to create dynamic fields
containing values from combining existing fields.
As with every other aspect of Django, usage of F() expressions has been clearly
documented in Django’s documentation for “Query
Expressions”.