Create JSON Response in Django with Model

Question

I am having some issue here. I am trying to return a JSON response made of a message and a model instance:

   class MachineModel(models.Model):
       name = models.CharField(max_length=64, blank=False)
       description = models.CharField(max_length=64, blank=False)
       manufacturer = models.ForeignKey(Manufacturer)
       added_by = models.ForeignKey(User, related_name='%(app_label)s_%(class)s_added_by')
       creation_date = models.DateTimeField(auto_now_add=True)
       last_modified = models.DateTimeField(auto_now=True)

    machine_model_model = form.save(commit=False)
    r_user = request.user.userprofile
    machine_model_model.manufacturer_id = manuf_id
    machine_model_model.added_by_id = request.user.id
    machine_model_model.save()
    alert_message = " The'%s' model " % machine_model_model.name
    alert_message += ("for '%s' " % machine_model_model.manufacturer)
    alert_message += "was was successfully created!"
    test = simplejson.dumps(list(machine_model_model))
    data = [{'message': alert_message, 'model': test}]
    response = JSONResponse(data, {}, 'application/json')


class JSONResponse(HttpResponse):
"""JSON response class."""
    def __init__(self, obj='', json_opts={}, mimetype="application/json", *args, **kwargs):
        content = simplejson.dumps(obj, **json_opts)
        super(JSONResponse,self).__init__(content, mimetype, *args, **kwargs)

But I keep getting:

File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/encoder.py", line 178, in default
raise TypeError(repr(o) + " is not JSON serializable")

TypeError: <MachineModel: "Test12"> is not JSON serializable

Why is that? I have seen before:

models = Model.objects.filter(manufacturer_id=m_id)
json = simplejson.dumps(models)

and that works... what is the difference?!

Thanks!

Answer 1

You should use django serializers instead of simplejson:

For example, this returns correctly serialized data:

from django.core import serializers
# serialize queryset
serialized_queryset = serializers.serialize('json', some_queryset)
# serialize object
serialized_object = serializers.serialize('json', [some_object,])