Django-piston: Difference between returning a queryset and a list?

I created this simple project to illustrate my problem.

These are my models:

class Zoo(models.Model):
    name = models.CharField(max_length=30)

class Animal(models.Model):
    name = models.CharField(max_length=30)
    zoo = models.ForeignKey(Zoo)

   开发者_运维问答 def speak(zelf):
        return 'woof woof'

This is my base handler:

class ZooHandler(BaseHandler):
    fields = ('id', 'name', 'speak')
    def read(self, request):
        z = Zoo.objects.get(pk=1)

        qs = z.animal_set.all()
        return qs

This is the result if I don't convert the queryset to a list:

[
    {
        "id": 1, 
        "name": "Tiger", 
        "speak": "woof woof"
    }, 
    {
        "id": 2, 
        "name": "Panda", 
        "speak": "woof woof"
    }, 
    {
        "id": 3, 
        "name": "Bear", 
        "speak": "woof woof"
    }, 
    {
        "id": 4, 
        "name": "Parrot", 
        "speak": "woof woof"
    }, 
    {
        "id": 5, 
        "name": "Dolphin", 
        "speak": "woof woof"
    }
]

This is what happens if I do convert it to a list return list(qs):

[
    {
        "zoo_id": 1, 
        "_state": "<django.db.models.base.ModelState object at 0x2413f90>", 
        "id": 1, 
        "name": "Tiger"
    }, 
    {
        "zoo_id": 1, 
        "_state": "<django.db.models.base.ModelState object at 0x241d590>", 
        "id": 2, 
        "name": "Panda"
    }, 
    {
        "zoo_id": 1, 
        "_state": "<django.db.models.base.ModelState object at 0x241d6d0>", 
        "id": 3, 
        "name": "Bear"
    }, 
    {
        "zoo_id": 1, 
        "_state": "<django.db.models.base.ModelState object at 0x241d750>", 
        "id": 4, 
        "name": "Parrot"
    }, 
    {
        "zoo_id": 1, 
        "_state": "<django.db.models.base.ModelState object at 0x241d7d0>", 
        "id": 5, 
        "name": "Dolphin"
    }
]

I lose the speak method result but gain a relational id and a _state object. Can anybody explain why this happens and how I can prevent it? This is just a test project I didn't wanna bore anybody trying to explain my real project.

Because you are not actually serializing Zoo objects, but Animal objects. Piston sees that you have a queryset of Animals, and tries to find an Animal handler - not finding one, it just serializes all the built-in objects, but not the custom method.

Define an AnimalHandler class and move the fields tuple to there, and it should work.