Mongokit - 查找最后添加的记录

Question

在用Python和Mongokit的时候，我遇到了一些问题，想要获取最后n条记录。对Python的语法不是很确定，但我写了：

record = collection.find(sort = [{'timestamp': DESCENDING}],limit=10)

但是我得到了这个错误：

Traceback (most recent call last):
  File "C:\Python26\lib\site-packages\flask-0.6-py2.6.egg\flask\app.py", line 874, in __call__
    return self.wsgi_app(environ, start_response)
  File "C:\Python26\lib\site-packages\flask-0.6-py2.6.egg\flask\app.py", line 864, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "C:\Python26\lib\site-packages\flask-0.6-py2.6.egg\flask\app.py", line 861, in wsgi_app
    rv = self.dispatch_request()
  File "C:\Python26\lib\site-packages\flask-0.6-py2.6.egg\flask\app.py", line 696, in dispatch_reque
st
    return self.view_functions[rule.endpoint](**req.view_args)
  File "E:\My Dropbox\Cranktrain\Blog\crankblog\apps\admin\views.py", line 24, in panel
    record = collection.find(sort = [{'timestamp': DESCENDING}],limit=10)
  File "C:\Python26\lib\site-packages\mongokit-0.5.13.1-py2.6.egg\mongokit\collection.py", line 67,
in find
    return Cursor(self, *args, **kwargs)
  File "C:\Python26\lib\site-packages\mongokit-0.5.13.1-py2.6.egg\mongokit\cursor.py", line 35, in _
_init__
    super(Cursor, self).__init__(*args, **kwargs)
  File "C:\Python26\lib\site-packages\pymongo-1.9-py2.6-win32.egg\pymongo\cursor.py", line 95, in __
init__
    self.__ordering = sort and helpers._index_document(sort) or None
  File "C:\Python26\lib\site-packages\pymongo-1.9-py2.6-win32.egg\pymongo\helpers.py", line 65, in _
index_document
    for (key, value) in index_list:
ValueError: need more than 1 value to unpack

如果能帮忙就太好了。

Answer 1

你应该给它一个 [(字段, 方向), ...] 的列表，而不是一个字典。

排序的规则必须是有顺序的；字典是没有顺序的。

不确定你是否需要用列表，试试直接用 (字段, 方向)。