Question

What I want to do is to set default values for a m2m field and I do it in a post_save signal. Here’s minimal code:

# models.py
class Question(models.Model):
    options = models.ManyToManyField(Option)
    body = models.CharField(max_length=140)

def default_options(sender, instance, created, **kwargs):
    if created and not instance.options.all():
        options = Option.objects.filter(id__in=[1, 2])
        instance.options.add(*options) 
        instance.save()

post_save.connect(default_options, sender=Question)

It works fine when “ordinary” saves are called:

>>> q=Question(body='test')
>>> q.save()
>>> q.options.all()
[<Option[1]>, <Option[2]>]

However, if the models are hooked with tastypie, options are never set..

# api.py 
class QuestionResource(ModelResource):
    options = fields.OneToManyField('qa.api.OptionResource', 'options', full=True, blank=True)
    class Meta:
        queryset = Question.objects.all()

# try to create a question:
curl --dump-header - -H "Content-Type: application/json" -X POST --data '{"body":"test"}' http://localhost:8000/api/0.1/question/

The server would respond a 201 but options of the question is not set.

My questions are:

• Am I right to use post-save signals to set default values for a m2m field?
• If so, what’s the hack with tastypie?
• If not, what’s the right way to do it?
• I noticed that the tastypie ManyToMany field has a default option. How to use it in this case or where can I find thorough documentation about it..

Answer 1

There are two possible way to handle the m2m relation at django-tastypie side.

One to to override the obj_create function. Here is for more help.

class QuestionResource(ModelResource):
   options = fields.OneToManyField('qa.api.OptionResource', 'options', full=True, blank=True)
   class Meta:
      queryset = Question.objects.all()

   def obj_create(self, bundle, request, **kwargs):
       print "hey we're in object create"
       # do something with bundle.data,
       return super(QuestionResource, self).obj_create(bundle, request, **kwargs)

And second way is to do it through curl request.

curl --dump-header - -H "Content-Type: application/json" -X POST --data '{"body":"test", "options": ["/api/v1/option/1/"]}' http://localhost:8000/api/0.1/question/