Django: Saving multiple ManyToMany fields within a transaction

Question

this is the representation of my models:

class B(models.Model):
   """I'm a dummy model, so doesn't pay atention of what I do"""
   name = models.CharField(max_length=250)

class A(models.Model):
   name = models.CharField(max_length=250)
   many_b = models.ManyToManyField(B)

Now, suppose I have a list of B objects. And a single A object that will be related to that Bs. Something like this:

a = A.objects.get(id=1)
list_of_b = [B<name='B1'>,B<name='B2'>,B<name='B3'>,]

The way I relate them now is this:

for b_object in list_of_b:
   a.many_b.add(b_object)

Is there any way to add all the B objects in a single transaction? Maybe in a single method, like:

a.many_b.addList(b) #This doesn't exist

Constantina

Answer 1

From the docs:

>>> john = Author.objects.create(name="John")
>>> paul = Author.objects.create(name="Paul")
>>> george = Author.objects.create(name="George")
>>> ringo = Author.objects.create(name="Ringo")
>>> entry.authors.add(john, paul, george, ringo)

So if you have a list, use argument expansion:

a.many_b.add(*list_of_b)

Tetragram

Thanks! Didn't know about the argument expansion. If the whole view is within a transaction is this call executed within that transaction? – Constantina

@Constantina Yes, the transaction middleware should put all writes in one transaction, including this. – Tetragram

Answer 2

I guess what you want is a kind of bulk insert right?

As far as I know this is just available in the Django TRUNK not in 1.3!

check it out some tutorial: http://www.caktusgroup.com/blog/2011/09/20/bulk-inserts-django/

Mandymandych

Yeah, something like that. I'll take a look. Thank you! – Constantina