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I'm having trouble to serialize the result array from a query where one of its projection is of datetime property.

My model class looks as follows: 

class ActivitySummaries(ndb.Model):
    registered_users = ndb.IntegerProperty()
    activated_users = ndb.IntegerProperty()
    company_registered = ndb.IntegerProperty()
    broker_registered = ndb.IntegerProperty()
    investor_registered = ndb.IntegerProperty()
    deal_approved = ndb.IntegerProperty()
    broker_approved = ndb.IntegerProperty()
    investor_approved = ndb.IntegerProperty()
    company_searched = ndb.IntegerProperty()
    broker_searched = ndb.IntegerProperty()
    investor_searched = ndb.IntegerProperty()
    watchlisting = ndb.IntegerProperty()
    closed_deals = ndb.IntegerProperty()
    timestamp = ndb.DateTimeProperty(auto_now_add=True)

Query:

activities = cls.query()

I want to send the the result array of the query in serialized form from Python using JSON and de-serialize in JavaScript using JSON.

I'm getting the following error:

raise TypeError(repr(o) + " is not JSON serializable")
TypeError: ActivitySummaries(key=Key('ActivitySummaries', 923), activated_users=0, broker_approved=0, broker_registered=0, broker_searched=1, closed_deals=0, company_registered=0, company_searched=1, deal_approved=0, investor_approved=0, investor_registered=0, investor_searched=0, registered_users=0, timestamp=datetime.datetime(2013, 5, 21, 22, 14, 28, 48000), watchlisting=0) is not JSON serializable

So I tried to use a subclass to handle the arbitrary value which is as follows:

import datetime
from json import JSONEncoder

class DateEncoder(JSONEncoder):
    def default(self, obj):
        if isinstance(obj, datetime.date):
            return obj.isoformat()
        return JSONEncoder.default(self, obj)

And call it using json.dumps(data, cls=DateEncoder)

But I still get the same error.

I have read somewhere that NDB Class has to_dict() built in method which we would normally call and then serialize the dictionary. Can any one help me out to serialize for this particular instance using to_dict(). I can provide you more details of the code if necessary.

P.S : My project is not using "Django" or "simplejson".

Newbie
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  • Have you searched SO before posting the question? http://stackoverflow.com/questions/13311363/appengine-making-ndb-models-json-serializable – dragonx May 21 '13 at 23:35
  • I did just answer your question http://stackoverflow.com/questions/16351286/python-query-objects-are-not-serializable – Tim Hoffman May 22 '13 at 01:11
  • possible duplicate of [JSON serialization of Google App Engine models](http://stackoverflow.com/questions/1531501/json-serialization-of-google-app-engine-models) – Lipis May 22 '13 at 07:56

1 Answers1

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Many options elsewhere. One of them, from http://blog.codevariety.com/2012/01/06/python-serializing-dates-datetime-datetime-into-json/:

def date_handler(obj):
    return obj.isoformat() if hasattr(obj, 'isoformat') else obj

print json.dumps(data, default=date_handler)

Note than in your example, you should have used 'default=' instead of 'cls='.

Felipe Hoffa
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