Django外键不变

Question

I have a funny(!) problem in Django. I want to change a Foreign key. my code:

print(todos[ind].list)
print(newList)
todos[ind].list = newList
print(todos[ind].list)
todos[ind].save()
print(todos[ind].list)

it's output:

oldList
newList
oldList
oldList

My Model:

class Todo(models.Model):
    name = models.CharField(max_length=255)
    list = models.ForeignKey(TodoList)

    def __str__(self):
        return str(self.name)

and todos list def:

todos = Todo.objects.filter(list = ls)

Where, ls and newList is:

ls = TodoList.objects.get(pk = list_id)
newList = TodoList.objects.get(pk = 1)

Thanks in advance.

Answer 1

todos is a list-like queryset but not a real list. Every time you access todos[ind] you get the hit into db and load new model instance.

So change you code to:

todo = todos[ind]

print(todo.list)
print(newList)
todo.list = newList
print(todo.list)
todo.save()
print(todo.list)

Or you can cache the queryset into list and then access to the instances by index like you did in your question:

todos = list(Todo.objects.filter(list=ls))

print(todos[ind].list)
todos[ind].list = newList
print(todos[ind].list)