Question

I have a large data set of Course objects in a Django application.

courses = Course.objects.all()

I want to make a copy of these courses, except the new courses have different semester values. I have tried this code:

for course in courses:
   newCourse = course
   newCourse.semester = 'Spring 2012'
   newCourse.save()

However, this code is not working. It is just changing the semesters of the current courses.

How do I make a copy of the old data set efficiently? Thank you.

Answer 1

As the documentation on how Django knows whether to update or insert shows, if an object has a primary key value set, Django will always do an update on that object.

So the simple way to clone an object is to set its pk – usually id – to None. Then, when you save, Django will create a new object.

newCourse.semester = 'Spring 2012'
newCourse.id = None
newCourse.save()