Django: convert QuerySet with related objects to JSON

Question

Let's suppose I have two simple Models:

class Place(models.Model):
    name = models.CharField(max_length=200)
    address = models.CharField(max_length=200)

class Event(models.Model):
    name = models.CharField(max_length=200)
    date = models.DateField()
    place = models.ForeignKey(Place)

What I want to do now is query a set of events with the resolved place, and convert everything to a list of dicts, that can be converted to JSON later on.

This is how the end result should look like:

[{
   "name": "event1",
   "date": "date1",
   "place": {
       "name": "place1",
       "address": "address1",
   },
},{
   "name": "event2",
   "date": "date2",
   "place": {
       "name": "place2",
       "address": "address2",
   },
},]

So far I tried my luck with ValueQuerySet and the .values() method:

Event.objects.all().select_related("place").values()

This however won't work, since .values() only returns the ids of related objects and not the content. So I was wondering if there is another built-in way to do this kind of conversion or if I have to iterate the QuerySet object and do the conversion by myself.

Answer 1

There is no default way to create the nested dicts you're after, but you can select the values of related items:

# No need for select_related in this case
Event.objects.values('name', 'date', 'place__name', 'place__address')

[{
   "name": "event1",
   "date": "date1",
   "place__name": "place1",
   "place__address": "address1",
},{
   "name": "event2",
   "date": "date2",
   "place__name": "place2",
   "place__address": "address2",
}]

If absolutely necessary, you can do some post-processing in Python to get the nested dicts you want.

Answer 2

There is a relevant method called model_to_dict :

from django.forms.models import model_to_dict
model_to_dict(instance, fields=[], exclude=[])

but it won't create dict fields from related models.

Here's the snippets you can use:

• http://djangosnippets.org/snippets/2342/
• http://djangosnippets.org/snippets/2670/

Hope that helps.