How to serialize Django queryset.values() into json?

Question

I have a model that has many fields, however for this problem I only need 3 of those fields. When I try to serialize a .values set I get an exception:

'dict' object has no attribute '_meta'

This is my code:

queryset = myModel.objects.filter(foo_icontains=bar).values('f1', 'f2', 'f3')
serialized_q = serializers.serialize('json', queryset, ensure_ascii=False)

Solution 1

Django serializers can only serialize queryset, values() does not return queryset rather ValuesQuerySet object. So, avoid using values(). Rather, specifiy the fields you wish to use in values(), in the serialize method as follows:

Look at this SO question for example

objectQuerySet = ConventionCard.objects.filter(ownerUser = user)
data = serializers.serialize('json', list(objectQuerySet), fields=('fileName','id'))

Instead of using objectQuerySet.values('fileName','id'), specify those fields using the fields parameter of serializers.serialize() as shown above.

Solution 2

As other people have said, Django's serializers can't handle a ValuesQuerySet. However, you can serialize by using a standard json.dumps() and transforming your ValuesQuerySet to a list by using list(). If your set includes Django fields such as Decimals, you will need to pass in DjangoJSONEncoder. Thus:

import json
from django.core.serializers.json import DjangoJSONEncoder

queryset = myModel.objects.filter(foo_icontains=bar).values('f1', 'f2', 'f3')
serialized_q = json.dumps(list(queryset), cls=DjangoJSONEncoder)

Solution 3

Make list from objectQuerySet:

data_ready_for_json = list( ConventionCard.objects.filter(ownerUser = user).values('fileName','id') )

Solution 4

My solution, It's work fine

from django.core.serializers import serialize
import json

permission_list = Permission.objects.all().order_by('-id')
permission_serialize= json.loads(serialize('json', permission_list))
return JsonResponse({'data': permission_serialize})

Solution 5

Just cast to dict every item and create json with json.dumps:

json.dumps([dict(item) for item in SomeModel.objects.all().values('id', 'title')])

View more solutions

Comments

[bash-]

Yes I am aware that .values() returns a list, however simplejson.dumps gives me a jsondata is not JSON serializable, the ValuesQuerySet is in the form: [{'key1': 'value1', 'key2': 'value2'}]

[Davor Lucic]

Yes, it depends on what data looks like, the first example from the linked answer is what you are looking for.

[Daniel Roseman]

@bash- just call list() on it first.

[Davor Lucic]

Yes list(ValuesQuerySet) should return list which can then be serialized with simplejson.

[bash-]

thanks, just a side note, in the SO question you linked, does that approach query the db for all the fields and then subset it for the 2 fields or would it only query the db for just those 2 fields?

[Davor Lucic]

I think it would query all fields, you could perhaps use only when querying. Though I am not quite sure. Debug it to see how the query looks like.

[Davor Lucic]

Remember that will only work if you get one result. list() solution will work in both cases.

[bash-]

@rebus thanks, it didn't work before because there was a DecimalField and it couldn't be serialized

[Kalob Taulien]

This was the quickest and simplest solution for me. I appended JsonResponse(data_ready_for_json, safe=False) and it worked perfectly in an Ajax call.

[Kyle_397]

Finally, this helped me which I want the Queryset to be converted to JSON and then returned to the template.

[user2162611]

I had similar problem. Above solution of using list(queryset) worked very well. Thanks Max!

[Code-Apprentice]

Why do you serialize() and then loads() just to have the JsonResponse serialize the list again. This is extra, unnecessary work.

[Shedrack]

This works like a charm!!!