CODEWITHSUNDEEP
django
Nips
Nips

Reputation: 13870

How to remove all relations from manytomany?

In one model, I have this:

class MyModel(models.Model):
    relations = models.ManyToManyField(OtherModel)
    ....

and if I choose:

my_object.relations.remove(other_model_object)

it works.

How to remove all objects from the relations? my_object.relations.clean() is not working.

Upvotes: 84

Views: 95344

Answers (5)

iamdipta
iamdipta

Reputation: 366

models.py

# consider Author & Book model
class Author(models.Model):
    name = models.CharField(max_length=200)

class Book(models.Model):
    authors = models.ManyToManyField(Author, related_name='books')
    title   = models.CharField(max_length=200)
    desc    = models.TextField()

Here, we assume that a book have many author & a authors have many book.

book (M) <------> (M) author

  1. now, we find a book all authors & some operations
books = Book.objects.all()
if len(books) > 0:
    book = books[0]

    # first book all authors
    first_book_all_authors = book.authors.all()
    
    # clear/remove all authors | (not same as delete)
    book.authors.clear()
    
    # add a author
    new_author = Author.objects.create(name = "Author name: Jhon smith")
    book.authors.add(new_author)

    # add multiple author
    all_authors = Author.objects.all()
    book.authors.set(all_authors)

    # remove a author
    auth1 = Author.objects.filter(pk = 1).first()
    book.authors.remove(auth1) # if auth1 is not None, then it's remove this author
  1. now, you find a author all books & some operations
authors = Author.objects.all()
if len(authors) > 0:
    auth = authors[0]

    # first author all book
    first_author_all_books1 = auth.books.all()   # if set related field name | related_name='books'
    first_author_all_books2 = auth.book_set.all() # if not set related field name | 'modelName'_set.all()
    
    # clear/remove all books | (not same as delete)
    auth.books.clear()
    
    # add a book
    new_book = Book.objects.create(title = "new book", desc="book desc")
    auth.books.add(new_book)

    # add multiple book
    all_books = Book.objects.all()
    auth.books.set(all_books)

    # remove a book
    book = Author.objects.filter(pk = 1).first()
    auth.books.remove(book) # if book is not None, then it's remove this book

NB: THINK SIMPLY

Upvotes: 5

camara90100
camara90100

Reputation: 892

Use my_object.relations.clear()

Upvotes: 28

Brandon Taylor
Brandon Taylor

Reputation: 34553

First, you'll need to clear the relationship(s) by using .clear() or .remove(), whichever suits your needs better according to the docs.

After that, you'll need to delete the object(s) by using the [YourModel].delete() method.

Upvotes: 90

Daniel Holmes
Daniel Holmes

Reputation: 2002

To remove all related objects without deleting them, just use:

my_object.relations.remove(*my_object.relations.all())

Upvotes: 4

Rachid
Rachid

Reputation: 2579

If you need to delete only the relationship for all instance between 2 models then you can do that by accessing the Manager of the relationship table. The m2m relationship table can be accessed via MyModel.relations.through so for deleting the relationships it becomes easy:

MyModel.relations.through.objects.all().delete()

reference:

https://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.ManyToManyField.through

Upvotes: 50

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