CODEWITHSUNDEEP
pythondjangopython-3.xdjango-models
MarkK
MarkK

Reputation: 1088

How to copy a Django Model Instance and all related data

Using Django 1.9 and Python 3.4 I want to copy an existing model instance and all its related data. Below is an example of how I have currently achieved this. My question is, is there a better way?

I have read over posts e.g. Duplicating model instances and their related objects in Django / Algorithm for recusrively duplicating an object this one but, they are over 8 years old and no longer work with Django 1.9+.

Below is how I try to achieve this already, ok or a better way in Django 1.9?

Models

class Book(models.Model):
     name = models.CharField(max_length=80)

class Contributor(models.Model):
     name = models.CharField(max_length=80)
     books = models.ForeignKey("Book", related_name="contributors")

The copy function. I have to recreate contributors after saving the new Book instance otherwise, it will assign existing contributors from the instance I'm copying from.

def copy_book(self, id):
    view = self.context['view']
    book_id = id
    book = Book.objects.get(pk=book_id)
    copy_book_contributors = book.contributors.all()

    book.id = None
    # make a copy of the contributors items.
    book.save()
    for item in copy_book_contributors:
        # We need to copy/save the item as it will reassign the existing one.
        item.id = None
        item.save()
        book.contributors.add(item)

Upvotes: 6

Views: 10330

Answers (1)

AKS
AKS

Reputation: 19831

For this particular case, you can bulk_create the contributors:

contributor_names = list(book.contributors.values_list('name', flat=True))

book.id = None
book.save()

# create the contributor object with the name and new book id.
contributors = [Contributor(name=name, book_id=book.id) for name in contributor_names]
Contributor.objects.bulk_create(contributors)

Upvotes: 6

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