Converting a django ValuesQuerySet to a json object

Question

I'm trying to use the ValuesQuerySet feature in Django to limit the number of fields returned from query to only those I need. I would like to serialize this data set a JSON object However, Django keeps throwing an error. Below I've included my code and the error I receive:

objectList = ConventionCard.objects.values('fileName','id').filter(ownerUser = user)
data = serializers.serialize('json', objectList)
return HttpResponse(data, mimetype='application/javascript')

The Error:

Exception Type:     AttributeError
Exception Value:    'dict' object has no attribute '_meta'
Exception Location:     C:\Python27\lib\site-packages\django\core\serializers\base.py in serialize, line 41

Thanks !

Why are you using values()? That makes dict objects which can't easily be serialized. — S.Lott
– S.Lott, Commented Jul 6, 2011 at 18:27
I don't want my entire object. I just want two fields. Values seems to be the way to do this. Is there a better way? — Karthik Ramachandran
– Karthik Ramachandran, Commented Jul 6, 2011 at 18:28
@S.Lott Values does exactly what it's suppose to do: it returns a subset of the fields. What doesn't work is the serialization of the resulting object. — Karthik Ramachandran
– Karthik Ramachandran, Commented Jul 6, 2011 at 18:39
@S.Lott "I'm trying to use the ValuesQuerySet feature in Django to limit the number of fields returned from query to only those I need." It was clear in the question. — Jordan Reiter
– Jordan Reiter, Commented Nov 4, 2011 at 15:00
@S.Lott True. I'm reminded of a poster once that said, Instead of saying "This doesn't make sense!" you should say "I don't understand." We all should work towards understanding. — Jordan Reiter
– Jordan Reiter, Commented Nov 11, 2011 at 15:55

Aaron · Accepted Answer · 2012-02-09 04:45:02Z

35

Cast the ValuesQuerySet to a list first:

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

list(query_set)

Removing the values call as suggested by ars causes the manager to pull all columns from the table, instead of only the two you need.

answered Feb 9, 2012 at 4:45

Aaron

8392 gold badges9 silver badges16 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

r_31415 Over a year ago

Brilliant answer. Works beautifully.

Ad N Over a year ago

It does not work in my environment (Python 3.4, Django 1.8.3).

andilabs · Accepted Answer · 2016-08-04 13:01:51Z

18

Try subsetting the fields in your values list through the serialize method using a QuerySet instead:

from django.core import serializers
objectQuerySet = ConventionCard.objects.filter(ownerUser = user)
data = serializers.serialize('json', objectQuerySet, fields=('fileName','id'))

edited Aug 4, 2016 at 13:01

andilabs

23.5k14 gold badges126 silver badges159 bronze badges

answered Jul 6, 2011 at 18:31

ars

124k23 gold badges151 silver badges135 bronze badges

2 Comments

Aaron Over a year ago

Not ideal because the query is pulling all column data out when it only needs the two fields.

Ashish Over a year ago

when i was trying this thing, i noticed that, serializers.serialize fields option, did not select the column/fields of related models. Anybody faced the same?

Henrik Andersson · Accepted Answer · 2019-01-02 06:38:50Z

14

I continued to get a dict object has no attribute _meta error when using the list() method above. However I found this snippet that does the trick

def ValuesQuerySetToDict(vqs):
    return [item for item in vqs]

# Usage
data = MyModel.objects.values('id','title','...','...')
data_dict = ValuesQuerySetToDict(data)
data_json = simplejson.dumps(data_dict)

edited Jan 2, 2019 at 6:38

Henrik Andersson

47.5k16 gold badges102 silver badges94 bronze badges

answered Jul 30, 2013 at 18:43

7wonders

1,6681 gold badge17 silver badges34 bronze badges

2 Comments

Jeel Shah Over a year ago

Module simplejson was removed in Django 1.5. The alternative is to simply import json and then use json.dumps(data_dict) and the answer is as expected.

Henrietta Martingale Over a year ago

This needs to be higher because the serializer has two flaws. 1. rest_framework also has serialzer, so you have to do from django.core import serializers as emily, and the second is the serializer doesnt' work on a queryset like this: statement_line.objects.select_related('ae').values('ae__opp_own', 'cur','ae_id').annotate(tots=Sum('amt'))

AJJ · Accepted Answer · 2012-12-17 15:25:42Z

1

Just to add a few details I've found:

When I tried @ars answer specifying the fields, like:

s_logs = serializers.serialize("json", logs, fields=('user', 'action', 'time'))

I get this:

[{"pk": 520, "model": "audit.auditlog", "fields": {"user": 3, "action": "create", "time":"2012-12-16T12:13:45.540"}}, ... ]

Which was not a simple serialization of the values as I wanted it.

So I tried the solution proposed by @Aaron, converting the valuesqueryset to a list, which didn't work the first time because the default encoder cannot deal with floats or datetime objects.

So I used @Aaron solution but using the JSON encoder that is used by django's serializer (DjangoJSONEncoder) by passing it as a kwarg to simplejson.dumps(), like this:

s_logs = list(logs.values('user', 'ip', 'object_name', 'object_type', 'action', 'time'))

return HttpResponse(simplejson.dumps( s_logs, cls=DjangoJSONEncoder ), mimetype='application/javascript')

answered Dec 17, 2012 at 15:25

AJJ

7,7277 gold badges33 silver badges35 bronze badges

1 Comment

defbyte Over a year ago

If you are using simplejson > 2.1, take a look at this issue: github.com/simplejson/simplejson/issues/37 Given that issue, one might have to subclass simplejson.JSONEncoder instead of json.JSONEncoder

Collectives™ on Stack Overflow

Converting a django ValuesQuerySet to a json object

4 Answers 4

2 Comments

2 Comments

2 Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

2 Comments

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related