How can I get computed elements of a table in a django queryset?

Question

I\'m trying to use django\'s queryset API to emulate the following query:

SELECT EXTRACT(year FROM chosen_date) AS year, 
EXTRACT(month FROM chosen_date) AS          


        

Answer 1

You could add a property to your model definition and then do :

@property
def chosen_date(self):
    return self.due_date if self.due_date else self.date

This assumes you can always fallback to date.If you prefer you can catch a DoesNotExist exception on due_date and then check for the second one.

You access the property as you would anything else.

As for the other query, I wouldn't use SQL to extract the y/m/d from the date, just use

model_instance.chosen_date.year

chosen_date should be a python date object (if you're using DateField in the ORM and this field is in a model)