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I have a django model called ServiceSubCategory and I want to create a JSON list of its primary key values using Python.

I have tried this:

idDic=[obj.as_json for obj in ServiceSubCategory.objects.values_list('id',flat=True)]

But I'm getting this error:

int object has no attribute as_json

I'm doing this because I'm gonna append another JSON to this later.

So how could I create a JSON out of my models primery Keys?

Update

I tried 

id_json = json.dumps(ServiceSubCategory.objects.values_list('id',flat=True))

And I'm getting a new error:

[1,2,3,4,5,6,7,8,9,10] is not JSON serializable

And this is the traceback:

Traceback: File "/usr/local/lib/python2.7/dist-packages/Django-1.7-py2.7.egg/django/core/handlers/base.py" in get_response 111. response = wrapped_callback(request, *callback_args, **callback_kwargs) File "/var/www/html/salimi/salimi/views.py" in service 61. idDic=json.dumps(ServiceSubCategory.objects.values_list('id',flat=True)) File "/usr/lib/python2.7/json/init.py" in dumps 243. return _default_encoder.encode(obj) File "/usr/lib/python2.7/json/encoder.py" in encode 207. chunks = self.iterencode(o, _one_shot=True) File "/usr/lib/python2.7/json/encoder.py" in iterencode 270. return _iterencode(o, 0) File "/usr/lib/python2.7/json/encoder.py" in default 184. raise TypeError(repr(o) + " is not JSON serializable")

Exception Type: TypeError at /service/1/ Exception Value: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] is not JSON serializable

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3 Answers 3

Reset to default
3

This should do the trick:

import json
json.dumps(list(ServiceSubCategory.objects.values_list('id', flat=True)))

values_list returns an instance of django.db.models.query.ValuesListQuerySet which does not have a default JSON serializer (it's just a QuerySet, no database request is made so far). However, you can transform it into a list object before.

import json
values_list_object = ServiceSubCategory.objects.values_list('id', flat=True))
list_object = list(values_list) # querying the database
json.dumps(list_object)
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Comments

1

You can simply write the following:

import json

id_json = json.dumps(list(ServiceSubCategory.objects.values_list('id',flat=True)))
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1 Comment

now I'm getting [1,2,3,4,5,6,7,8,9,10] is not JSON serializable
1

Update

It looks like ServiceSubCategory.objects.values_list('id', flat=True) might return a generator. In that case you can consume the generator using list():

import json
json.dumps(list(ServiceSubCategory.objects.values_list('id', flat=True)))

Wouldn't this do the trick?

import json
json.dumps(ServiceSubCategory.objects.values_list('id', flat=True))

Since ServiceSubCategory.objects.values_list is already a list it can be dumped directly to JSON. There is no need to use a list comprehension.

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6 Comments

now I'm getting [1,2,3,4,5,6,7,8,9,10] is not JSON serializable
@AlexJolig: Could you post the traceback for that error, and the output of repr(ServiceSubCategory.objects.values_list). Also, are you after a list of JSON strings, or the list converted to JSON (as this answer attempts)?
Updated the answer with traceback and I guess it would be better if I get the JSON values as string
@Selcuk: well thanks for that. It would have been nice if you could have rolled it back to the most recent edit.
@mhawke Sorry, your last edit wasn't there when I rolled it back. Must be a clash.
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