Question

通过Udacity课程＆＃34;数据争夺MongoDB＆＃34;他们有以下问题。我试着解决（如下所示）。但是，它给了我Python错误，我不确定是什么错误。

它正在进行的JSON格式是：

{
    "_id" : ObjectId("5304e2e3cc9e684aa98bef97"),
    "text" : "First week of school is over :P",
    "in_reply_to_status_id" : null,
    "retweet_count" : null,
    "contributors" : null,
    "created_at" : "Thu Sep 02 18:11:25 +0000 2010",
    "geo" : null,
    "source" : "web",
    "coordinates" : null,
    "in_reply_to_screen_name" : null,
    "truncated" : false,
    "entities" : {
        "user_mentions" : [ ],
        "urls" : [ ],
        "hashtags" : [ ]
    },
    "retweeted" : false,
    "place" : null,
    "user" : {
        "friends_count" : 145,
        "profile_sidebar_fill_color" : "E5507E",
        "location" : "Ireland :)",
        "verified" : false,
        "follow_request_sent" : null,
        "favourites_count" : 1,
        "profile_sidebar_border_color" : "CC3366",
        "profile_image_url" : "http://a1.twimg.com/profile_images/1107778717/phpkHoxzmAM_normal.jpg",
        "geo_enabled" : false,
        "created_at" : "Sun May 03 19:51:04 +0000 2009",
        "description" : "",
        "time_zone" : null,
        "url" : null,
        "screen_name" : "Catherinemull",
        "notifications" : null,
        "profile_background_color" : "FF6699",
        "listed_count" : 77,
        "lang" : "en",
        "profile_background_image_url" : "http://a3.twimg.com/profile_background_images/138228501/149174881-8cd806890274b828ed56598091c84e71_4c6fd4d8-full.jpg",
        "statuses_count" : 2475,
        "following" : null,
        "profile_text_color" : "362720",
        "protected" : false,
        "show_all_inline_media" : false,
        "profile_background_tile" : true,
        "name" : "Catherine Mullane",
        "contributors_enabled" : false,
        "profile_link_color" : "B40B43",
        "followers_count" : 169,
        "id" : 37486277,
        "profile_use_background_image" : true,
        "utc_offset" : null
    },
    "favorited" : false,
    "in_reply_to_user_id" : null,
    "id" : NumberLong("22819398300")
}

这里的代码包含说明：

#!/usr/bin/env python
"""
Write an aggregation query to answer this question:

Of the users in the "Brasilia" timezone who have tweeted 100 times or more,
who has the largest number of followers?

The following hints will help you solve this problem:
- Time zone is found in the "time_zone" field of the user object in each tweet.
- The number of tweets for each user is found in the "statuses_count" field.
  To access these fields you will need to use dot notation (from Lesson 4)
- Your aggregation query should return something like the following:
{u'ok': 1.0,
 u'result': [{u'_id': ObjectId('52fd2490bac3fa1975477702'),
                  u'followers': 2597,
                  u'screen_name': u'marbles',
                  u'tweets': 12334}]}
Note that you will need to create the fields 'followers', 'screen_name' and 'tweets'.

Please modify only the 'make_pipeline' function so that it creates and returns an aggregation 
pipeline that can be passed to the MongoDB aggregate function. As in our examples in this lesson,
the aggregation pipeline should be a list of one or more dictionary objects. 
Please review the lesson examples if you are unsure of the syntax.

Your code will be run against a MongoDB instance that we have provided. If you want to run this code
locally on your machine, you have to install MongoDB, download and insert the dataset.
For instructions related to MongoDB setup and datasets please see Course Materials.

Please note that the dataset you are using here is a smaller version of the twitter dataset used 
in examples in this lesson. If you attempt some of the same queries that we looked at in the lesson 
examples, your results will be different.
"""

def get_db(db_name):
    from pymongo import MongoClient
    client = MongoClient('localhost:27017')
    db = client[db_name]
    return db

def make_pipeline():
    # complete the aggregation pipeline
    pipeline = [
        { 
            "$match": {
                         "user.time_zone": "Brasilia",
                         "user.statuses_count": {"$gte": 100}
                      }
        },
        { 
            "$sort": { "$user.friends_count", -1}
        },
        {
            "$limit": 1
        },
        { 
            "$project": {
                           "followers": "$user.friends_count",
                           "screen_name": "$user.screen_name",
                           "tweets": "$user.statuses_count"
                        }
        }

    ]
    return pipeline

def aggregate(db, pipeline):
    result = db.tweets.aggregate(pipeline)
    return result

if __name__ == '__main__':
    db = get_db('twitter')
    pipeline = make_pipeline()
    result = aggregate(db, pipeline)
    import pprint
    pprint.pprint(result)
    assert len(result["result"]) == 1
    assert result["result"][0]["followers"] == 17209

以下是它给我的错误：

Traceback (most recent call last):
  File "vm_main.py", line 33, in <module>
    import main
  File "/tmp/vmuser_hnypkpkult/main.py", line 2, in <module>
    import studentMain
  File "/tmp/vmuser_hnypkpkult/studentMain.py", line 43, in <module>
    result = aggregate(db, pipeline)
  File "/tmp/vmuser_hnypkpkult/studentMain.py", line 37, in aggregate
    result = db.tweets.aggregate(pipeline)
  File "/usr/local/lib/python2.7/dist-packages/pymongo/collection.py", line 1390, in aggregate
    "aggregate", self.__name, **command_kwargs)
  File "/usr/local/lib/python2.7/dist-packages/pymongo/database.py", line 338, in _command
    for doc in cursor:
  File "/usr/local/lib/python2.7/dist-packages/pymongo/cursor.py", line 1076, in next
    if len(self.__data) or self._refresh():
  File "/usr/local/lib/python2.7/dist-packages/pymongo/cursor.py", line 1020, in _refresh
    self.__uuid_subtype))
bson.errors.InvalidDocument: Cannot encode object: set(['$user.friends_count', -1])

Answer 1

您的$sort子句被解释为Python集而不是字典。另外，我认为你需要在该条款中没有美元符号的情况下引用该字段。将其更改为以下内容（请注意冒号而不是逗号）：

{ 
    "$sort": { "user.friends_count": -1}
},

在MongoDB中排序错误

1 个答案: