How to serialize to JSON a list of model objects in django/python

Question

I am trying to serialize a list of model object defined as:

class AnalysisInput(models.Model):
    input_user = models.CharField(max_length=45)
    input_title = models.CharField(max_length=45)
    input_date = models.DateTimeField()
    input_link = models.CharField(max_length=100)

I wrote a custom serializer (encoder) for json.dumps():

class AnalysisInputEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, AnalysisInput):
            return { "input_id" : obj.id,
                    "input_user" : obj.input_user,
                    "input_title" : obj.input_title,
                    "input_date" : obj.input_date.isoformat(),
                    "input_link" : obj.input_link }
        return json.JSONEncoder.default(self, obj)

When I serialize only one object, I am able to do it. When I try to serialize a list of object I get

[ objects..] is not JSON serializable

I searched but I didn't find where to work on.. I was thinking about writing a custom serializer also for list of model object.

Answer 1

A custom encoder is not called recursively. You are actually better off not using a custom encoder, and instead convert your objects to simple python types before serializing.

You could add a as_json or similarly named method to your model and calling that every time you need a JSON result:

class AnalysisInput(models.Model):
    input_user = models.CharField(max_length=45)
    input_title = models.CharField(max_length=45)
    input_date = models.DateTimeField()
    input_link = models.CharField(max_length=100)

    def as_json(self):
        return dict(
            input_id=self.id, input_user=self.input_user,
            input_title=self.input_title, 
            input_date=self.input_date.isoformat(),
            input_link=self.input_link)

Then in your view:

# one result
return HttpResponse(json.dumps(result.as_json()), content_type="application/json")

# a list of results
results = [ob.as_json() for ob in resultset]
return HttpResponse(json.dumps(results), content_type="application/json")

Answer 2

The best way I found to serialize your Django models is by using django.core.serializers to serialize your model list into JSON, XML, or YAML. No custom serialization code required! Documentation is here: https://docs.djangoproject.com/en/dev/topics/serialization/

Here is my implementation:

lead/models.py:

from django.db import models

class Lead(models.Model):
    name = models.CharField(max_length=50)
    email = models.CharField(max_length=256)
    phone = models.CharField(max_length=20)
    twitter_handle = models.CharField(max_length=20)
    github_handle = models.CharField(max_length=20)

lead/views.py:

from django.http import HttpResponse
from django.core import serializers
from lead.models import Lead

def index(request):
    leads_as_json = serializers.serialize('json', Lead.objects.all())
    return HttpResponse(leads_as_json, content_type='json')

The end result:

[{"pk": 1, "model": "lead.lead", "fields": {"twitter_handle": "johndoe", "name": "John Doe", "phone": "1(234)567-8910", "email": "john@doe.com", "github_handle": "johndoe"}}]

Answer 3

Simplest solution:

def index(request):
    data = serializers.serialize('json', Product.objects.all())
    return HttpResponse(data, content_type='application/json')