JSON response in Google App Engine with Python

Question

I want to build a REST service with Python and Google App Engine and have the following code:

Edited Code:

import webapp2
from google.appengine.ext import db
from google.appengine.api import users
import json

class Item(db.Model):

    author           = db.UserProperty(required=False)
    summary          = db.StringProperty(required=True)
    description      = db.StringProperty(multiline=True)
    url              = db.StringProperty()
    created          = db.DateTimeProperty(auto_now_add=True)
    updated          = db.DateTimeProperty(auto_now=True)
    dueDate          = db.StringProperty(required=True)
    finished         = db.BooleanProperty()

class GetAllItems(webapp2.RequestHandler):
    def get(self):
        item = Item(summary="Summary", dueDate="Date")
        item.put()

        allItems = Item.all()
        data = []
        for entry in allItems:
            data.append(db.to_dict(entry))

        self.response.out.write(json.dumps(entry))

app = webapp2.WSGIApplication(
    [
        ('/api/items', GetAllItems)
        ],
    debug=True)

How can i convert all items of this model into JSON and send it back as JSON? I always get this Error:

TypeError: <main.Item object at 0x0538B590> is not JSON serializable

ManfredP · Accepted Answer · 2015-12-12 16:59:21Z

I use now NDB instead of DB and the following code solved all my problems:

import decimal
import webapp2
from google.appengine.ext import ndb
import json
from google.appengine.api import users


class Item(ndb.Model):
    author = ndb.UserProperty(required=False)
    summary = ndb.StringProperty(required=True)
    description = ndb.StringProperty()
    url = ndb.StringProperty()
    created = ndb.DateTimeProperty(auto_now_add=True)
    updated = ndb.DateTimeProperty(auto_now=True)
    updated = ndb.StringProperty()
    dueDate = ndb.StringProperty(required=True)
    finished = ndb.BooleanProperty()


class DateTimeEncoder(json.JSONEncoder):
    def default(self, obj):
        if hasattr(obj, 'isoformat'):
            return obj.isoformat()
        elif isinstance(obj, decimal.Decimal):
            return float(obj)
        else:
            return json.JSONEncoder.default(self, obj)


class GetAllItems(webapp2.RequestHandler):
    def get(self):
        item = Item(summary="Summary", dueDate="Date")
        item.put()

        text = json.dumps([i.to_dict() for i in Item.query().fetch()], cls=DateTimeEncoder)
        self.response.out.write(text)


app = webapp2.WSGIApplication(
    [
        ('/api/items', GetAllItems)
    ],
    debug=True)

masnun · Accepted Answer · 2015-12-12 14:50:41Z

0

Use db.to_dict to convert a model to a dictionary and then you can do json.dumps on it.

class GetAllItems(webapp2.RequestHandler):
    def get(self):
        item = Item(summary="Summary", dueDate="Date")
        item.put()

        all_items = Item.all()
        data = []
        for entry in all_items:
            data.append(db.to_dict(entry))

        self.response(json.dumps(data))

edited Dec 12, 2015 at 14:50

answered Dec 12, 2015 at 14:41

masnun

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2 Comments

ManfredP Over a year ago

With my model i get now this error: TypeError: <main.Item object at 0x0538B590> is not JSON serializable

masnun Over a year ago

This is weird. Try debugging the type of db.to_dict(entry)

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