Django data migration when changing a field to ManyToMany

Question

I have a Django application in which I want to change a field from a ForeignKey to a ManyToManyField. I want to preserve my old data. What is the simplest/best process to

Answer 1

Probably the best and easiest thing you should do would be:

Create the Many to many field with a different name say

authors = models.ManyToManyField(Author)

write a small function to convert foreignkey values to M2M values:

def convert():
    books = Book.objects.all()
    for book in books:
        if book.author:
            li = [book.author.id]
            book.authors.append(li)
            book.save()

Once it is run, you can delete the author field from the table and run migration again.