CODEWITHSUNDEEP
jsondjangodjango-viewsdjango-queryset
Daniel
Daniel

Reputation: 1061

Django View: Return Queryset in JSON Format

i am trying to make the following view with return JsonResponse() at the end work correctly:

def get_data(request):
    full_data = Fund.objects.all()
    data = {
    "test2": full_data.values('investment_strategy').annotate(sum=Sum('commitment')),
    }
    return JsonResponse(data)

However, I get an error message saying "Object of type QuerySet is not JSON serializable". When I put the above Queryset in a view with return render() at the end:

def get_more_data(request):
    full_data = Fund.objects.all()
    data = {"test2": full_data.values('investment_strategy').annotate(sum=Sum('commitment'))}
    return render (request, 'test.html', data)

I get the the following result: <QuerySet [{'investment_strategy': 'Buyout', 'sum': 29}, {'investment_strategy': 'Growth', 'sum': 13}, {'investment_strategy': 'Miscellaneous', 'sum': 14}, {'investment_strategy': 'Venture Capital', 'sum': 23}, {'investment_strategy': 'n/a', 'sum': 36}]>

So the queryset works fine, I just have no clue how to return the data in proper Json format (which I would need to use the data charts.js)

I looked through answers for similar questions such as: TypeError: object is not JSON serializable in DJango 1.8 Python 3.4 Output Django queryset as JSON etc. but could not find a meaningful solution for my problem.

Any help would be much appreciated!

Upvotes: 1

Views: 3352

Answers (3)

Eduardo Poiate
Eduardo Poiate

Reputation: 85

The best way I found was to create a custom QuerySet and Manager, it's not a lot of code and it is reusable!

I began by creating the custom QuerySet:

# managers.py but you can do that in the models.py too
from django.db import models

class DictQuerySet(models.QuerySet):

    def dict(self):
        values = self.values()
        result = {}
        for value in values:
            id = value['id']
            result[id] = value # you can customize the content of your dictionary here
        return result

Then I created a custom Manager, it is optional but i prefer this way.

# managers.py, also optional
class DictManager(models.Manager):

    def get_queryset(self):
        return DictQuerySet(self.model, using=self._db)

Change the default manager in your model:

# models.py
from .managers import DictManager

class Fund(models.Model):
    # ...
    objects =  DictManager()
    # ...

And now you can call the dict() method from the query

# views.py 

def get_data(request):
    full_data = Fund.objects.all().dict()
    return JsonResponse(full_data)

The response will be the full_data as a dictionary of dictionaries and each key is the primary key of the corresponding object.

If you intend to keep the same format for your JSONs, then you can use the same custom manager for all your models.

Upvotes: 0

Daniel
Daniel

Reputation: 1061

So I managed to find a solution, that worked for me - in case anyone else has the same problem. I changed my view to the following:

def get_data(request):
    full_data = Fund.objects.all()
    full_data_filtered = full_data.values('investment_strategy').annotate(sum=Sum('commitment'))

labels = []
values = []

for d in full_data_filtered:
    labels.append(d['investment_strategy'])
    values.append(d['sum'])

data = {
    "labels": labels,    
    "values": values,
    }

return JsonResponse(data)

So basically I iterate over the Queryset and assign the values I need to lists, which can be passed to JsonResponse. I don't know if this is the most elegant way to do this (sure not), but it works and I can render my data in charts.js

Upvotes: 3

dirkgroten
dirkgroten

Reputation: 20682

JsonResponse(list(data)) will evaluate the Queryset (actually perform the query to the database) and turn it into a list that can be passed to JsonResponse.

This works because you use values and annotate, so the list is a list of dictionaries containing serializable fields.

In the example you mentioned, it didn't work because the Queryset was just returning a list of model instances, so wrapping in list() isn't enough. If you hadn't added values, you'd have had a list of Fund instances which are not serializable.

Upvotes: 0

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