Google App Engine 模型的 JSON 序列化 [英] JSON serialization of Google App Engine models

问题描述

我一直在寻找，但没有成功.我的项目没有使用 Django，是否有一种简单的方法可以将 App Engine 模型 (google.appengine.ext.db.Model) 序列化为 JSON，或者我是否需要编写自己的序列化程序?

I've been searching for quite a while with no success. My project isn't using Django, is there a simple way to serialize App Engine models (google.appengine.ext.db.Model) into JSON or do I need to write my own serializer?

型号:

class Photo(db.Model):
    filename = db.StringProperty()
    title = db.StringProperty()
    description = db.StringProperty(multiline=True)
    date_taken = db.DateTimeProperty()
    date_uploaded = db.DateTimeProperty(auto_now_add=True)
    album = db.ReferenceProperty(Album, collection_name='photo')

推荐答案

一个简单的递归函数可用于将实体(和任何引用对象)转换为可传递给 simplejson 的嵌套字典:

A simple recursive function can be used to convert an entity (and any referents) to a nested dictionary that can be passed to simplejson:

import datetime
import time

SIMPLE_TYPES = (int, long, float, bool, dict, basestring, list)

def to_dict(model):
    output = {}

    for key, prop in model.properties().iteritems():
        value = getattr(model, key)

        if value is None or isinstance(value, SIMPLE_TYPES):
            output[key] = value
        elif isinstance(value, datetime.date):
            # Convert date/datetime to MILLISECONDS-since-epoch (JS "new Date()").
            ms = time.mktime(value.utctimetuple()) * 1000
            ms += getattr(value, 'microseconds', 0) / 1000
            output[key] = int(ms)
        elif isinstance(value, db.GeoPt):
            output[key] = {'lat': value.lat, 'lon': value.lon}
        elif isinstance(value, db.Model):
            output[key] = to_dict(value)
        else:
            raise ValueError('cannot encode ' + repr(prop))

    return output

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