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Serialize GQL to json
# Copyright 2008 Google Inc.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.
"""Utility classes and methods for use with simplejson and appengine.
Provides both a specialized simplejson encoder, GqlEncoder, designed to simplify
encoding directly from GQL results to JSON. A helper function, encode, is also
provided to further simplify usage.
GqlEncoder: Adds support for GQL results and properties to simplejson.
encode(input): Direct method to encode GQL objects as JSON.
import datetime
import time
from django.utils import simplejson
from google.appengine.api import users
from google.appengine.ext import db
class GqlEncoder(simplejson.JSONEncoder):
"""Extends JSONEncoder to add support for GQL results and properties.
Adds support to simplejson JSONEncoders for GQL results and properties by
overriding JSONEncoder's default method.
# TODO Improve coverage for all of App Engine's Property types.
def default(self, obj):
"""Tests the input object, obj, to encode as JSON."""
if hasattr(obj, '__json__'):
return getattr(obj, '__json__')()
if isinstance(obj, db.GqlQuery):
return list(obj)
elif isinstance(obj, db.Model):
properties =
output = {}
if hasattr(obj, 'NO_JSON'):
filtered = obj.NO_JSON
filtered = []
for field, value in properties:
if field in filtered:
output[field] = getattr(obj, field)
return output
elif isinstance(obj, datetime.datetime):
output = {}
fields = ['day', 'hour', 'microsecond', 'minute', 'month', 'second',
methods = ['ctime', 'isocalendar', 'isoformat', 'isoweekday',
for field in fields:
output[field] = getattr(obj, field)
for method in methods:
output[method] = getattr(obj, method)()
output['epoch'] = time.mktime(obj.timetuple())
return output
elif isinstance(obj, time.struct_time):
return list(obj)
elif isinstance(obj, db.Key):
return {'type':obj.kind(), 'id' }
elif isinstance(obj, users.User):
output = {}
methods = ['nickname', 'email']
for method in methods:
output[method] = getattr(obj, method)()
return output
return simplejson.JSONEncoder.default(self, obj)
def encode(input):
"""Encode an input GQL object as JSON
input: A GQL object or DB property.
A JSON string based on the input object.
TypeError: Typically occurs when an input object contains an unsupported
return GqlEncoder().encode(input)
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