Question

I have a model like this:

class Book(models.Model):
     authors = models.ManyToManyField(User) # User is a separate model
     readers = models.ManyToManyField(User)
     # ... rest of code

I’m trying to create a function outside my views which takes three inputs: a Book, a string and a User. The User is added to the Book’s ManyRelatedManager whose corresponding field name matches the string.

For example, if the function were called foo:

def foo(book, field_name, user):
    f = #... this is where I need help, should be a ManyRelatedManager that belongs to 'book'
    f.add(user)
    book.save()

Calling foo(Book.objects.get(id=1), 'authors', User.objects.get(id=1)) would result in the User with id 1 being added to the field ‘authors’ in the Book with id 1. Similarly, calling foo(Book.objects.get(id=1), 'readers', User.objects.get(id=1)) would result in the User with id 1 being added to the field ‘readers’ in the Book with id 1.

I tried using Book._meta.get_field() but this returned the ManyToManyField itself, not a ManyRelatedManager. Is there some sort of built-in way to get the ManyRelatedManager whose field name matches a string?

Sorry if that description is confusing, my problem is hard to put into words. If anyone can understand my problem, your help is appreciated. Thanks!

Answer 1

getattr() can get an attribute from an object from a string passed to it.