poll.id来自哪里？

Question

I'm studying the DjangoTutorial03 , and don't quite understand where the id from poll.id comes from.

poll.question I get it, it's one of the attributes of class Poll in models.py . But not so much for poll.id . Is it an attribute inherited from models.Model ? I'm not sure because I searched for self.id in both base.py & __init__.py from /django/db/models/ and nothing showed up. (is it the right place to search for?)

Answer 1

The id field is automatically created for your model if you don't provide any other field with primary_key=True keyword argument. A good practice when dealing with primary keys is to use pk attribute, as opposed to id , because pk is an alias to the real primary key field be it id , my_id , or anything else - poll.id and poll.pk are both the same.

The behaviour is caused by the Options class ( here ) which is what you get when you access _meta attribute, and it's attributes are derived from Model.Meta .