python 如何将 db.Model 对象序列化为 json？
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How to serialize db.Model objects to json?
提问by Jader Dias
When using
使用时
from django.utils import simplejson
on objects of types that derive from db.Modelit throws exceptions. How to circumvent this?
在从db.Model它派生的类型的对象上抛出异常。如何规避这种情况？
采纳答案by Jader Dias
Since I could not find an appropriate solution I wrote my own, which is not exactly a JSON serializer, but a Javascript serializer
由于找不到合适的解决方案，我自己编写了自己的解决方案，这不完全是 JSON 序列化程序，而是 Javascript 序列化程序
from google.appengine.ext import db
from google.appengine.api.datastore_types import *
def dumpStr(obj):
return "'" + obj + "'"
def dumps(obj):
if isinstance(obj, str):
return dumpStr(obj)
elif obj == None:
return None
elif isinstance(obj, list):
items = [];
for item in obj:
items.append(dumps(item))
return '[' + ','.join(items) + ']'
elif isinstance(obj, datetime.datetime):
return "new Date('%s')" % obj.ctime()
properties = [];
for property in dir(obj):
if property[0] != '_':
value = obj.__getattribute__(property)
valueClass = str(value.__class__)
if not(('function' in valueClass) or ('built' in valueClass) or ('method' in valueClass)):
value = dumps(value)
if value != None:
properties.append("'" + property + "':" + value)
if len(properties) == 0:
return str(obj)
else:
return '{' + ','.join(properties) + '}'
回答by spidee
Ok - my python not great so any help would be appreciated - You dont need to write a parser - this is the solution:
好的 - 我的 python 不是很好，所以任何帮助将不胜感激 - 您不需要编写解析器 - 这是解决方案：
add this utlity class http://code.google.com/p/google-app-engine-samples/source/browse/trunk/geochat/json.py?r=55
添加此实用程序类http://code.google.com/p/google-app-engine-samples/source/browse/trunk/geochat/json.py?r=55
import datetime
import time
from google.appengine.api import users
from google.appengine.ext import db
#this is a mod on the orinal file for some reason it includes its own simplejson files i have ref django!
from django.utils import simplejson
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)
save as json.py
另存为 json.py
TO USE
使用
import cgi
import os
import json
from google.appengine.ext.webapp import template
from google.appengine.api import users
from google.appengine.ext import webapp
from google.appengine.ext.webapp.util import run_wsgi_app
from google.appengine.ext import db
class Greeting(db.Model):
author = db.UserProperty()
content = db.StringProperty(multiline=True)
date = db.DateTimeProperty(auto_now_add=True)
class MainPage(webapp.RequestHandler):
def get(self):
greetings_query = Greeting.all().order('-date')
greetings = greetings_query.fetch(5)
if users.get_current_user():
url = users.create_logout_url(self.request.uri)
url_linktext = 'Logout'
else:
url = users.create_login_url(self.request.uri)
url_linktext = 'Login'
template_values = {
'greetings': greetings,
'url': url,
'url_linktext': url_linktext,
}
path = os.path.join(os.path.dirname(__file__), 'index.html')
self.response.out.write(template.render(path, template_values))
class Guestbook(webapp.RequestHandler):
def post(self):
greeting = Greeting()
if users.get_current_user():
greeting.author = users.get_current_user()
greeting.content = self.request.get('content')
greeting.put()
self.redirect('/')
#here i return my json feed - simple implementaion for example
class FeedHandler(webapp.RequestHandler):
def get(self):
"""Retrieve a feed"""
user = None
greetings_query = Greeting.all().order('-date')
rs= greetings_query.fetch(5)
#this is the part that calls the encoder - dosnt cause an exception
data = json.encode(rs)
#roll out to browser -might need to check my headers etc
self.response.headers['Content-Type'] = 'application/json; charset=utf-8'
self.response.out.write(data)
application = webapp.WSGIApplication(
[
('/', MainPage),
('/sign',Guestbook),
('/feed',FeedHandler),
], debug=True
)
def main():
run_wsgi_app(application)
if __name__ == "__main__":
main()
This is the browser response:
这是浏览器响应：
[{"content": "", "date": {"ctime": "Sat Jan 23 02:40:22 2010", "hour": 2, "isoweekday": 6, "month": 1, "second": 22, "microsecond": 434000, "isocalendar": [2010, 3, 6], "timetuple": [2010, 1, 23, 2, 40, 22, 5, 23, -1], "year": 2010, "epoch": 1264214422.0, "isoformat": "2010-01-23T02:40:22.434000", "day": 23, "minute": 40}, "author": {"nickname": "[email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}, {"content": "", "date": {"ctime": "Sat Jan 23 01:12:43 2010", "hour": 1, "isoweekday": 6, "month": 1, "second": 43, "microsecond": 972000, "isocalendar": [2010, 3, 6], "timetuple": [2010, 1, 23, 1, 12, 43, 5, 23, -1], "year": 2010, "epoch": 1264209163.0, "isoformat": "2010-01-23T01:12:43.972000", "day": 23, "minute": 12}, "author": {"nickname": "[email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}, {"content": "test", "date": {"ctime": "Fri Jan 22 22:32:13 2010", "hour": 22, "isoweekday": 5, "month": 1, "second": 13, "microsecond": 659000, "isocalendar": [2010, 3, 5], "timetuple": [2010, 1, 22, 22, 32, 13, 4, 22, -1], "year": 2010, "epoch": 1264199533.0, "isoformat": "2010-01-22T22:32:13.659000", "day": 22, "minute": 32}, "author": {"nickname": "[email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}, {"content": "", "date": {"ctime": "Fri Jan 22 22:29:49 2010", "hour": 22, "isoweekday": 5, "month": 1, "second": 49, "microsecond": 358000, "isocalendar": [2010, 3, 5], "timetuple": [2010, 1, 22, 22, 29, 49, 4, 22, -1], "year": 2010, "epoch": 1264199389.0, "isoformat": "2010-01-22T22:29:49.358000", "day": 22, "minute": 29}, "author": {"nickname": "[email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}, {"content": "ah it works!\r\n", "date": {"ctime": "Fri Jan 22 22:29:22 2010", "hour": 22, "isoweekday": 5, "month": 1, "second": 22, "microsecond": 995000, "isocalendar": [2010, 3, 5], "timetuple": [2010, 1, 22, 22, 29, 22, 4, 22, -1], "year": 2010, "epoch": 1264199362.0, "isoformat": "2010-01-22T22:29:22.995000", "day": 22, "minute": 29}, "author": {"nickname": "[email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}]
[{"content": "", "date": {"ctime": "Sat Jan 23 02:40:22 2010", "hour": 2, "isoweekday": 6, "month": 1, "second ": 22, "微秒": 434000, "isocalendar": [2010, 3, 6], "timetuple": [2010, 1, 23, 2, 40, 22, 5, 23, -1], "年" : 2010, "epoch": 1264214422.0, "isoformat": "2010-01-23T02:40:22.434000", "day": 23, "minute": 40}, "author": {"nickname": "test@" example.com", "email": "[email protected]", "auth_domain": "gmail.com"}}, {"content": "", "date": {"ctime": "Sat Jan 23 01:12:43 2010", "hour": 1, "isoweekday": 6, "month": 1,"second": 43, "microsecond": 972000, "isocalendar": [2010, 3, 6], "timetuple": [2010, 1, 23, 1, 12, 43, 5, 23, -1], "年”：2010，“纪元”：1264209163.0，“isoformat”：“2010-01-23T01:12:43.972000”，“日”：23，“分钟”：12}，“作者”：{“昵称”：“ [email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}, {"content": "test", "date": {"ctime": " Fri Jan 22 22:32:13 2010", "hour": 22, "isoweekday": 5, "month": 1, "second": 13, "microsecond": 659000, "isocalendar": [2010, 3, 5], "timetuple": [2010, 1, 22, 22, 32, 13, 4, 22, -1], "年":2010, "epoch": 1264199533.0, "isoformat": "2010-01-22T22:32:13.659000", "day": 22, "minute": 32}, "author": {"nickname": "test@example .com", "email": "[email protected]", "auth_domain": "gmail.com"}}, {"content": "", "date": {"ctime": "Fri Jan 22 22 :29:49 2010", "hour": 22, "isoweekday": 5, "month": 1, "second": 49, "microsecond": 358000, "isocalendar": [2010, 3, 5], " timetuple": [2010, 1, 22, 22, 29, 49, 4, 22, -1], "year": 2010, "epoch": 1264199389.0, "isoformat": "2010-01-22T22:59:4003. ", "day": 22, "minute": 29}, "author": {"昵称”：“[email protected]”，“电子邮件”：“[email protected]”，“auth_domain”：“gmail.com”}}，{“内容”：“啊它有效！\r\n” , "date": {"ctime": "Fri Jan 22 22:29:22 2010", "hour": 22, "isoweekday": 5, "month": 1, "second": 22, "microsecond": 995000, "isocalendar": [2010, 3, 5], "timetuple": [2010, 1, 22, 22, 29, 22, 4, 22, -1], "year": 2010, "epoch": 1264199362. , "isoformat": "2010-01-22T22:29:22.995000", "day": 22, "minute": 29}, "author": {"nickname": "[email protected]", "email" ：“[email protected]”，“auth_domain”：“gmail.com”}}][email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}, {"content": "啊它有效！\r\n", "date" : {"ctime": "Fri Jan 22 22:29:22 2010", "hour": 22, "isoweekday": 5, "month": 1, "second": 22, "microsecond": 995000, "isocalendar" ": [2010, 3, 5], "timetuple": [2010, 1, 22, 22, 29, 22, 4, 22, -1], "year": 2010, "epoch": 1264199362.0, "isoformat" : "2010-01-22T22:29:22.995000", "day": 22, "minute": 29}, "author": {"nickname": "[email protected]", "email": "test@ example.com", "auth_domain": "gmail.com"}}][email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}, {"content": "啊它有效！\r\n", "date" : {"ctime": "Fri Jan 22 22:29:22 2010", "hour": 22, "isoweekday": 5, "month": 1, "second": 22, "microsecond": 995000, "isocalendar" ": [2010, 3, 5], "timetuple": [2010, 1, 22, 22, 29, 22, 4, 22, -1], "year": 2010, "epoch": 1264199362.0, "isoformat" : "2010-01-22T22:29:22.995000", "day": 22, "minute": 29}, "author": {"nickname": "[email protected]", "email": "test@ example.com", "auth_domain": "gmail.com"}}][email protected]", "auth_domain": "gmail.com"}}, {"content": "啊它有效！\r\n", "date": {"ctime": "Fri Jan 22 22: 29:22 2010", "hour": 22, "isoweekday": 5, "month": 1, "second": 22, "microsecond": 995000, "isocalendar": [2010, 3, 5], "timetuple ": [2010, 1, 22, 22, 29, 22, 4, 22, -1], "year": 2010, "epoch": 1264199362.0, "isoformat": "2010-01-22T22:29:22.995000 , "day": 22, "minute": 29}, "author": {"nickname": "[email protected]", "email": "[email protected]", "auth_domain": "gmail. com"}}][email protected]", "auth_domain": "gmail.com"}}, {"content": "啊它有效！\r\n", "date": {"ctime": "Fri Jan 22 22: 29:22 2010", "hour": 22, "isoweekday": 5, "month": 1, "second": 22, "microsecond": 995000, "isocalendar": [2010, 3, 5], "timetuple ": [2010, 1, 22, 22, 29, 22, 4, 22, -1], "year": 2010, "epoch": 1264199362.0, "isoformat": "2010-01-22T22:29:22.995000 , "day": 22, "minute": 29}, "author": {"nickname": "[email protected]", "email": "[email protected]", "auth_domain": "gmail. com"}}]: "啊它有效！\r\n", "date": {"ctime": "Fri Jan 22 22:29:22 2010", "hour": 22, "isoweekday": 5, "month": 1 , "second": 22, "microsecond": 995000, "isocalendar": [2010, 3, 5], "timetuple": [2010, 1, 22, 22, 29, 22, 4, 22, -1], “年”：2010，“纪元”：1264199362.0，“isoformat”：“2010-01-22T22:29:22.995000”，“日”：22，“分钟”：29}，“作者”：{“昵称”： "[email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}]: "啊它有效！\r\n", "date": {"ctime": "Fri Jan 22 22:29:22 2010", "hour": 22, "isoweekday": 5, "month": 1 , "second": 22, "microsecond": 995000, "isocalendar": [2010, 3, 5], "timetuple": [2010, 1, 22, 22, 29, 22, 4, 22, -1], “年”：2010，“纪元”：1264199362.0，“isoformat”：“2010-01-22T22:29:22.995000”，“日”：22，“分钟”：29}，“作者”：{“昵称”： "[email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}]second": 22, "microsecond": 995000, "isocalendar": [2010, 3, 5], "timetuple": [2010, 1, 22, 22, 29, 22, 4, 22, -1], "year ": 2010, "epoch": 1264199362.0, "isoformat": "2010-01-22T22:29:22.995000", "day": 22, "minute": 29}, "author": {"nickname": "test @example.com", "email": "[email protected]", "auth_domain": "gmail.com"}}]second": 22, "microsecond": 995000, "isocalendar": [2010, 3, 5], "timetuple": [2010, 1, 22, 22, 29, 22, 4, 22, -1], "year ": 2010, "epoch": 1264199362.0, "isoformat": "2010-01-22T22:29:22.995000", "day": 22, "minute": 29}, "author": {"nickname": "test @example.com", "email": "[email protected]", "auth_domain": "gmail.com"}}][email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}][email protected]", "email": "[email protected]", "auth_domain": "gmail.com"}}]
回答by John P
The example provided by Jader Dias works fine for my concern after some twaeking. Remove the encode method as it contains a circular reference. The adjusted class should look like:
经过一些调整后，Jader Dias 提供的示例可以很好地解决我的问题。删除 encode 方法，因为它包含循环引用。调整后的类应如下所示：
import datetime
import time
from google.appengine.api import users
from google.appengine.ext import db
from django.utils import simplejson
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, datetime.date):
output = {}
fields = ['year', 'month', 'day']
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)
As I've saved this class in a file called utils.py and when appropriate I import it using
因为我已经将这个类保存在一个名为 utils.py 的文件中，并且在适当的时候我使用
import utils
Then I just call utils.GqlEncoder().encode(results), for example:
然后我只调用utils.GqlEncoder().encode(results)，例如：
query = User.all()
results = query.fetch(10)
self.response.headers['Content-Type'] = "text/plain" # Alt. application/json
self.response.out.write( utils.GqlEncoder().encode(results) )
The result should look something like this (I've added some line feeds in order to make it a bit easier to read):
结果应该看起来像这样（我添加了一些换行符，以便更容易阅读）：
[
{"date": {"ctime": "Tue Feb 23 10:41:21 2010", "hour": 10, "isoweekday": 2, "month": 2,
"second": 21, "microsecond": 495535, "isocalendar": [2010, 8, 2], "timetuple": [2010, 2, 23, 10, 41, 21, 1, 54, -1],
"year": 2010, "epoch": 1266921681.0, "isoformat": "2010-02-23T10:41:21.495535", "day": 23, "minute": 41},
"claimed_id": "https:\/\/www.google.com\/accounts\/o8\/id?id=abcdefghijklmnopqrstuvxyz",
"display_name": "Alfred E Neumann",
"email": null,
"full_name": "Alfred E Neumann"
},
{"date": {"ctime": "Tue Feb 23 11:00:54 2010", "hour": 11, "isoweekday": 2, "month": 2,
"second": 54, "microsecond": 805261, "isocalendar": [2010, 8, 2], "timetuple": [2010, 2, 23, 11, 0, 54, 1, 54, -1],
"year": 2010, "epoch": 1266922854.0, "isoformat": "2010-02-23T11:00:54.805261", "day": 23, "minute": 0},
"claimed_id": "http:\/\/openid.domain.net\/john",
"display_name": "",
"email": "[email protected]",
"full_name": "John Parnefjord"
}
]
回答by BrainCore
json cannot be used to serialize anything more than basic types such as dicts, lists, ints/longs, and strings (this is not comprehensive). For example, even these simple commands do not work:
json 不能用于序列化除基本类型之外的任何内容，例如 dicts、lists、ints/longs 和 strings（这并不全面）。例如，即使这些简单的命令也不起作用：
import json
json.dumps(object())
If you want to serialize django objects, you should refer to the django documentation on serialization, which will use their own libraries, but they do do support json.
如果你想序列化 django 对象，你应该参考关于序列化的django 文档，它将使用他们自己的库，但他们确实支持 json。
回答by spidee
From what i can understand - and i am new to python - with google app engine the work around is to serialize the model object to a dictioanry python object and then use simple json to dump it as a json string - this makes no sense to me - maybe someone has the know to serialise to a ditionary (pickel?) Any help on this would be HELP! not to impressed that google app engine has no inbuilt solution for this.
据我所知 - 我是 python 的新手 - 使用谷歌应用程序引擎，解决方法是将模型对象序列化为字典 python 对象，然后使用简单的 json 将其转储为 json 字符串 - 这对我来说没有意义- 也许有人知道连载到字典（pickel？）对此有任何帮助！不要给谷歌应用引擎没有内置解决方案留下深刻印象。
