GAE에서 DB의 검색 결과를 JSON 포맷으로 가져오기

Google App Engine에서는 django를 기본으로 제공합니다. django를 사용하여 View와 Logic을 구분할 수도 있지만, 이 뿐만 아니라 simplejson을 사용할 수 있기 때문에 서버로부터 DB의 데이터를 JSON 포맷로 가져오거나 서버로 JSON 포맷의 데이터를 보내 DB를 업데이트 하는 동작을 할 수 있습니다. 물론 JSON Parser가 필요하지만, 왠만한 모든 언어로 포팅이 되어 있습니다.

더 편한 방법이 있겠지만, 구글의 예제 중 simplejson.JSONEncoder를 상속받은 GqlEncoder를 사용하면 매우 편하게 GqlQuery의 결과를 JSON으로 뿌릴 수 있습니다.

json.py...

[code python]
# 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
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# 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 simplejson
import time

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 = obj.properties().items()
output = {}
for field, value in properties:
output[field] = getattr(obj, field)
return output

elif isinstance(obj, datetime.datetime):
output = {}
fields = ['day', 'hour', 'microsecond', 'minute', 'month', 'second',
'year']
methods = ['ctime', 'isocalendar', 'isoformat', 'isoweekday',
'timetuple']
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, users.User):
output = {}
methods = ['nickname', 'email', 'auth_domain']
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

Args:
input: A GQL object or DB property.

Returns:
A JSON string based on the input object.

Raises:
TypeError: Typically occurs when an input object contains an unsupported
type.
"""
return GqlEncoder().encode(input) [/code]

아래는 위 파일을 가져다가 사용한 예제입니다. 바로 사용 가능한 완벽한 예제는 아닙니다.

펼쳐두기..

[code python]

import json

class Question(db.Model)
  author = db.StringProperty()
  date = db.DateTimeProperty(auto_now_add=True)

class MainPage(webapp.RequestHandler):
  def get(self):
    questions_query = Question.all().order('-date')
    questions = questions_query.fetch(10)
    encoded_result = json.encode(questions)

    self.response.headers['Content-Type'] = 'text/plain'
    self.response.out.write(encoded_result)

[/code]

나중에 시간나면, 간단하지만 뭔소리인지 모르겠는 json.py를 뜯어 보겠습니다. 일단 문제 해결!