伙计们，我只是花了很多时间来尝试查找-我应该缺少一些基本知识。

我有一个python对象，我要做的就是将此对象插入mondodb中。

这就是我所拥有的：

from pymongo import Connection
import json

conn = Connection()
db = conn.cl_database
postings = db.postings_collection

class Posting(object):
    def __init__(self, link, found=None, expired=None):
        self.link = link
        self.found = found
        self.expired = expired

posting = Posting('objectlink1')
value = json.dumps(posting, default=lambda x:x.__dict__)
postings.insert(value)

抛出此错误：

Traceback (most recent call last):
  File "./mongotry.py", line 21, in <module>
postings.insert(value)
  File "build/bdist.macosx-10.7-intel/egg/pymongo/collection.py", line 302, in insert
  File "build/bdist.macosx-10.7-intel/egg/pymongo/database.py", line 252, in _fix_incoming
  File "build/bdist.macosx-10.7-intel/egg/pymongo/son_manipulator.py", line 73, in transform_incoming
TypeError: 'str' object does not support item assignment

好像是因为json.dumps（）返回一个字符串。

现在，如果我在插入之前对值进行加载，则效果很好：

posting = Posting('objectlink1')
value = json.dumps(posting, default=lambda x:x.__dict__)
value = json.loads(value)
postings.insert(value)

最直接的方法是什么？

谢谢！