233

There is a lot of documentation on how to serialize a Model QuerySet but how do you just serialize to JSON the fields of a Model Instance?

4
  • While it looks like you can serialize a queryset of 1 object, you cannot use the classes from django.core to do this. Any particular reason not to use serialize the queryset? Commented Apr 16, 2009 at 17:03
  • 1
    The queryset serializer wraps the result in two more layers than it has to. So you have to do data[0].fields.name instead of data.name. Commented Apr 16, 2009 at 17:37
  • That's what I thought. I ran into that same issue when I was writing a GWT interface for a django backend. Looks like David might be onto something. Commented Apr 16, 2009 at 17:48
  • possible duplicate of Django serializer for one object Commented Jan 26, 2015 at 14:49

23 Answers 23

323

You can easily use a list to wrap the required object and that's all what django serializers need to correctly serialize it, eg.:

from django.core import serializers

# assuming obj is a model instance
serialized_obj = serializers.serialize('json', [ obj, ])
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12 Comments

But in response you are required to index zero element of the JSON object to get to the serialized object. Just something to note.
And how about serializing all referenced objects along with the root object?
Don't you want [0] at the end of your last line, like @DavorLucic suggested? And no need for trailing comma in your list literal (for the love of PEP8 ;).
Deserialization also requires an extra step; see stackoverflow.com/a/29550004/2800876
This didn't work for me. Django throws AttributeError 'tuple' object has no attribute '_meta'
|
124

If you're dealing with a list of model instances the best you can do is using serializers.serialize(), it gonna fit your need perfectly.

However, you are to face an issue with trying to serialize a single object, not a list of objects. That way, in order to get rid of different hacks, just use Django's model_to_dict (if I'm not mistaken, serializers.serialize() relies on it, too):

from django.forms.models import model_to_dict

# assuming obj is your model instance
dict_obj = model_to_dict( obj )

You now just need one straight json.dumps call to serialize it to json:

import json
serialized = json.dumps(dict_obj)

That's it! :)

2 Comments

this fails with UUID fields, should be clear otherwise
fails with datetime fields. Solved it this way json.loads(serialize('json', [obj]))[0] while serializer is django.core.serializers.serialize
47

To avoid the array wrapper, remove it before you return the response:

import json
from django.core import serializers

def getObject(request, id):
    obj = MyModel.objects.get(pk=id)
    data = serializers.serialize('json', [obj,])
    struct = json.loads(data)
    data = json.dumps(struct[0])
    return HttpResponse(data, mimetype='application/json')

I found this interesting post on the subject too:

http://timsaylor.com/convert-django-model-instances-to-dictionaries

It uses django.forms.models.model_to_dict, which looks like the perfect tool for the job.

3 Comments

if this is the best way to serialize a single model in django, then that is horrible as one should not need to deserialize the json and serialize it back.
@Herbert, perhaps. But there it is. If you have a better way, I'm all ears. This shouldn't have much practical downside as fetching and de/re encoding a single object shouldn't be that resource-intensive. Make it into a helper function or extend/mix-in with your objects as a new method if you want to hide the horror.
Hiding the horror is not the problem and maybe not even this solution; what surprises me is that this is django's best way of doing it.
34

There is a good answer for this and I'm surprised it hasn't been mentioned. With a few lines you can handle dates, models, and everything else.

Make a custom encoder that can handle models:

from django.forms import model_to_dict
from django.core.serializers.json import DjangoJSONEncoder
from django.db.models import Model

class ExtendedEncoder(DjangoJSONEncoder):

    def default(self, o):

        if isinstance(o, Model):
            return model_to_dict(o)

        return super().default(o)

Now use it when you use json.dumps. The superclass DjangoJSONEncoder can handle dates, datetime, timedelta, Decimal, Promise, and UUID objects which aren't natively supported by json.dumps.

json.dumps(data, cls=ExtendedEncoder)

Now models, dates and everything can be serialized and it doesn't have to be in an array or serialized and unserialized. Anything you have that is custom can just be added to the default method.

You can even use Django's native JsonResponse this way:

from django.http import JsonResponse

JsonResponse(data, encoder=ExtendedEncoder)

3 Comments

This solution is simple and elegant. The encoder can be used with both json.dumps and json.dump methods. This way you don't need to change the workflow of the application because you use custom objects or add another method call prior to converting to json. Just add your conversion code in the encoder and you are ready to go.
Object of type MyModel is not JSON serializable
@AlxVallejo you didn't add the part about model_to_dict or you aren't calling it right.
14

If you're asking how to serialize a single object from a model and you know you're only going to get one object in the queryset (for instance, using objects.get), then use something like:

import django.core.serializers
import django.http
import models

def jsonExample(request,poll_id):
    s = django.core.serializers.serialize('json',[models.Poll.objects.get(id=poll_id)])
    # s is a string with [] around it, so strip them off
    o=s.strip("[]")
    return django.http.HttpResponse(o, mimetype="application/json")

which would get you something of the form:

{"pk": 1, "model": "polls.poll", "fields": {"pub_date": "2013-06-27T02:29:38.284Z", "question": "What's up?"}}

2 Comments

But that will strip all the square brackets, not just the outside ones. Better? "o=s[1:-1]" ?
@Julian str.strip only strips outer characters - so all good!
13

If you want to return the single model object as a json response to a client, you can do this simple solution:

from django.forms.models import model_to_dict
from django.http import JsonResponse

movie = Movie.objects.get(pk=1)
return JsonResponse(model_to_dict(movie))

Comments

12

It sounds like what you're asking about involves serializing the data structure of a Django model instance for interoperability. The other posters are correct: if you wanted the serialized form to be used with a python application that can query the database via Django's api, then you would wan to serialize a queryset with one object. If, on the other hand, what you need is a way to re-inflate the model instance somewhere else without touching the database or without using Django, then you have a little bit of work to do.

Here's what I do:

First, I use demjson for the conversion. It happened to be what I found first, but it might not be the best. My implementation depends on one of its features, but there should be similar ways with other converters.

Second, implement a json_equivalent method on all models that you might need serialized. This is a magic method for demjson, but it's probably something you're going to want to think about no matter what implementation you choose. The idea is that you return an object that is directly convertible to json (i.e. an array or dictionary). If you really want to do this automatically:

def json_equivalent(self):
    dictionary = {}
    for field in self._meta.get_all_field_names()
        dictionary[field] = self.__getattribute__(field)
    return dictionary

This will not be helpful to you unless you have a completely flat data structure (no ForeignKeys, only numbers and strings in the database, etc.). Otherwise, you should seriously think about the right way to implement this method.

Third, call demjson.JSON.encode(instance) and you have what you want.

2 Comments

I haven't tried the code yet but I just wanted to point out some errors in it. It is instance._meta.get_all_field_names() and getattribute is a function so should have () and not [].
in addition to FK, this will not work for datetime fields (unless there is magic in demjson.JSON.encode)
10

.values() is what I needed to convert a model instance to JSON.

.values() documentation: https://docs.djangoproject.com/en/3.0/ref/models/querysets/#values

Example usage with a model called Project.

Note: I'm using Django Rest Framework

from django.http import JsonResponse

@csrf_exempt
@api_view(["GET"])
def get_project(request):
    id = request.query_params['id']
    data = Project.objects.filter(id=id).values()
    if len(data) == 0:
        return JsonResponse(status=404, data={'message': 'Project with id {} not found.'.format(id)})
    return JsonResponse(data[0])

Result from a valid id:

{
    "id": 47,
    "title": "Project Name",
    "description": "",
    "created_at": "2020-01-21T18:13:49.693Z",
}

1 Comment

Missing from django.http import JsonResponse
6

Here's my solution for this, which allows you to easily customize the JSON as well as organize related records

Firstly implement a method on the model. I call is json but you can call it whatever you like, e.g.:

class Car(Model):
    ...
    def json(self):
        return {
            'manufacturer': self.manufacturer.name,
            'model': self.model,
            'colors': [color.json for color in self.colors.all()],
        }

Then in the view I do:

data = [car.json for car in Car.objects.all()]
return HttpResponse(json.dumps(data), content_type='application/json; charset=UTF-8', status=status)

1 Comment

In Python 3, it becomes car.json()
5

I solved this problem by adding a serialization method to my model:

def toJSON(self):
    import simplejson
    return simplejson.dumps(dict([(attr, getattr(self, attr)) for attr in [f.name for f in self._meta.fields]]))

Here's the verbose equivalent for those averse to one-liners:

def toJSON(self):
    fields = []
    for field in self._meta.fields:
        fields.append(field.name)

    d = {}
    for attr in fields:
        d[attr] = getattr(self, attr)

    import simplejson
    return simplejson.dumps(d)

_meta.fields is an ordered list of model fields which can be accessed from instances and from the model itself.

2 Comments

Although the idea might seem good at first, one should point out that there are consequences to using this approach. You are tying one specific serialization output to your model.
@JonasGeiregat since this method is defined on a model-to-model basis, what's wrong with the approach? Sadly this seems to be the only way to return a json object that contains both the fields and the primary key of the instance.
5

Use Django Serializer with python format,

from django.core import serializers

qs = SomeModel.objects.all()
serialized_obj = serializers.serialize('python', qs)

What's difference between json and python format?

The json format will return the result as str whereas python will return the result in either list or OrderedDict

2 Comments

that's too unfortunate
I get OrderedDict, not dict
4

Use list, it will solve problem

Step1:

 result=YOUR_MODELE_NAME.objects.values('PROP1','PROP2').all();

Step2:

 result=list(result)  #after getting data from model convert result to list

Step3:

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

2 Comments

This seems like it'll still serialize as a json array (of objects) not a naked object, which is what OP asked about. iow, this is no different than the regular serialize method.
This will fail with a JSON serialization error. Queryset objects are not serializable
4

To serialize and deserialze, use the following:

from django.core import serializers

serial = serializers.serialize("json", [obj])
...
# .next() pulls the first object out of the generator
# .object retrieves django object the object from the DeserializedObject
obj = next(serializers.deserialize("json", serial)).object

2 Comments

I'm getting 'generator object has no attribute 'next'. Any idea?
@user2880391 I've updated this for Python 3. Does that fix it?
2

All of these answers were a little hacky compared to what I would expect from a framework, the simplest method, I think by far, if you are using the rest framework:

rep = YourSerializerClass().to_representation(your_instance)
json.dumps(rep)

This uses the Serializer directly, respecting the fields you've defined on it, as well as any associations, etc.

1 Comment

In my case it doesn't work with ModelSerializer
1

It doesn't seem you can serialize an instance, you'd have to serialize a QuerySet of one object.

from django.core import serializers
from models import *

def getUser(request):
    return HttpResponse(json(Users.objects.filter(id=88)))

I run out of the svn release of django, so this may not be in earlier versions.

1 Comment

whats the point of this framework if it cant do the most basic thing, serialize a damn model with the most commonly used format.
1
ville = UneVille.objects.get(nom='lihlihlihlih')
....
blablablab
.......

return HttpResponse(simplejson.dumps(ville.__dict__))

I return the dict of my instance

so it return something like {'field1':value,"field2":value,....}

1 Comment

this will break: TypeError: <django.db.models.base.ModelState object at 0x7f2b3bf62310> is not JSON serializable
1

how about this way:

def ins2dic(obj):
    SubDic = obj.__dict__
    del SubDic['id']
    del SubDic['_state']
return SubDic

or exclude anything you don't want.

Comments

1

Might have missed this, but this seems cleanest:

>>> import json
>>> from django.forms.models import model_to_dict

>>> json.dumps(model_to_dict(my_instance))
'{"code": "AG", "ordering": null, "aliases": ["types"], ...

(aliases above is a successfully serialized JSONField.)

If it is going straight into a response, as @flowfelis suggests use django.http.JsonResponse(model_to_dict(my_instance)).

Comments

0

This is a project that it can serialize(JSON base now) all data in your model and put them to a specific directory automatically and then it can deserialize it whenever you want... I've personally serialized thousand records with this script and then load all of them back to another database without any losing data.

Anyone that would be interested in opensource projects can contribute this project and add more feature to it.

serializer_deserializer_model

Comments

0

Let this is a serializers for CROPS, Do like below. It works for me, Definitely It will work for you also.

First import serializers

from django.core import serializers

Then you can write like this

class CropVarietySerializer(serializers.Serializer): 
    crop_variety_info = serializers.serialize('json', [ obj, ])

OR you can write like this

class CropVarietySerializer(serializers.Serializer): 
    crop_variety_info = serializers.JSONField() 

Then Call this serializer inside your views.py For more details, Please visit https://docs.djangoproject.com/en/4.1/topics/serialization/ serializers.JSONField(*args, **kwargs) and serializers.JSONField() are same. you can also visit https://www.django-rest-framework.org/api-guide/fields/ for JSONField() details.

Comments

0

you can use something like this if you have nested objects as well.

from django.forms import model_to_dict
from django.core.serializers.json import DjangoJSONEncoder
from django.db.models import Model, QuerySet
class ExtendedEncoder(DjangoJSONEncoder):

    def default(self, o):
        if isinstance(o, Model):
            return model_to_dict(o)
        if isinstance(o, QuerySet):
            return [obj for obj in o]

        return super().default(o)

Comments

0

You can use a custom function to achieve that.

def model_to_dict_custom(instance):
model_dict = {}
# Iterate through the model instance's fields
for field in instance._meta.fields:
    field_name = field.name
    field_value = getattr(instance, field_name)
    # Convert special types if needed (e.g., datetime to string)
    if hasattr(field_value, 'strftime'):
        field_value = field_value.strftime('%Y-%m-%d %H:%M:%S')
    model_dict[field_name] = field_value
return model_dict

Comments

-1

from django.core import serializers as core_serializers

seedproducerob=commoncertificate.objects.filter(golobalcat=bussnesscatvalue).order_by('-publisheddate')

data = core_serializers.serialize('python', seedproducerob)

return JsonResponse(data,status=200,safe=False)

1 Comment

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