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    【已解决】Python的pymongo中随机输出一个集合的记录

    Python crifan 1574浏览 0评论
    折腾：
    【记录】用Flask实现测评系统的后端
    期间，
    需要实现MongoDB中，random随机获取一个，evaluation.question的collection
    之前知道有find和find_one，但是只想要获取随机的一个
    mongodb find return random
    Random record from MongoDB – Stack Overflow
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    // Get one random document from the mycoll collection.
    db.mycoll.aggregate([{ $sample: { size: 1 } }])
    先去本地mongo命令行中试试
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    ➜  mongodb mongo
    MongoDB shell version v3.6.3
    connecting to:
    mongodb://127.0.0.1:27017
    MongoDB server version: 3.6.3
    Server has startup warnings:
    2018-12-19T17:51:17.268+0800 I CONTROL  [initandlisten]
    2018-12-19T17:51:17.268+0800 I CONTROL  [initandlisten] ** WARNING: Access control is not enabled for the database.
    2018-12-19T17:51:17.268+0800 I CONTROL  [initandlisten] **          Read and write access to data and configuration is unrestricted.
    2018-12-19T17:51:17.268+0800 I CONTROL  [initandlisten]
    2018-12-19T17:51:17.268+0800 I CONTROL  [initandlisten] ** WARNING: This server is bound to localhost.
    2018-12-19T17:51:17.268+0800 I CONTROL  [initandlisten] **          Remote systems will be unable to connect to this server.
    2018-12-19T17:51:17.268+0800 I CONTROL  [initandlisten] **          Start the server with --bind_ip <address> to specify which IP
    2018-12-19T17:51:17.268+0800 I CONTROL  [initandlisten] **          addresses it should serve responses from, or with --bind_ip_all to
    2018-12-19T17:51:17.268+0800 I CONTROL  [initandlisten] **          bind to all interfaces. If this behavior is desired, start the
    2018-12-19T17:51:17.268+0800 I CONTROL  [initandlisten] **          server with --bind_ip 127.0.0.1 to disable this warning.
    2018-12-19T17:51:17.268+0800 I CONTROL  [initandlisten]
    > show databases
    Scholastic   0.039GB
    admin        0.000GB
    config       0.000GB
    dialog       0.272GB
    evaluation   0.000GB
    gridfs      13.792GB
    local        0.000GB
    log          0.000GB
    storybook    0.101GB
    test         0.000GB
    > use evaluation
    switched to db evaluation
    > show collections
    question
    > db.question.aggregate([{$sample: {size: 1}}])
    { "_id" : ObjectId("5c1777e1cc6df4563adf4b7e"), "question_number" : 304, "major_type" : "单选", "stem_text" : "When will the party start?", "max_answer_time" : 30, "difficulty" : "1.2", "audio_length" : 0, "ave_answer_time" : 15, "sub_questions" : [ { "option_type" : "text", "question_texts" : [ "" ], "options" : [ { "option_number" : 1, "option_image" : "", "option_text" : "In the morning." }, { "option_number" : 2, "option_image" : "", "option_text" : "In the evening." }, { "option_number" : 3, "option_image" : "", "option_text" : "At night." } ], "correct_option" : [ 2 ] } ], "checkpoint" : [ "reading", "general_reading", "句子理解", "", "" ], "stem_image" : "image/party board.png", "audio" : "", "audio_text" : "", "stem_type" : "mix" }
    > db.question.aggregate([{$sample: {size: 1}}]).pretty
    function () {
        this._prettyShell = true;
        return this;
    }
    > db.question.aggregate([{$sample: {size: 1}}]).pretty()
    {
        "_id" : ObjectId("5c1777e2cc6df4563adf4cd1"),
        "question_number" : 643,
        "major_type" : "单选",
        "stem_text" : "Who ___ you maths last Sunday?",
        "max_answer_time" : 10,
        "difficulty" : 2,
        "audio_length" : 0,
        "ave_answer_time" : 5,
        "sub_questions" : [
            {
                "option_type" : "text",
                "question_texts" : [
                    ""
                ],
                "options" : [
                    {
                        "option_number" : 1,
                        "option_image" : "",
                        "option_text" : "taught"
                    },
                    {
                        "option_number" : 2,
                        "option_image" : "",
                        "option_text" : "teaches"
                    },
                    {
                        "option_number" : 3,
                        "option_image" : "",
                        "option_text" : "teach"
                    }
                ],
                "correct_option" : [
                    1
                ]
            }
        ],
        "checkpoint" : [
            "reading",
            "grammar",
            "",
            "",
            ""
        ],
        "stem_image" : "",
        "audio" : "",
        "audio_text" : "",
        "stem_type" : "text"
    }
    >
    再去pymongo中试试是否支持
    pymongo aggregate
    Aggregation Examples — PyMongo 3.7.2 documentation
    需要PyMongo版本>= 2.1.0
    去看看此处版本
    Pipfile
    中只有：
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    flask-pymongo = "*"
    没有版本，去看看pipenv graph
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    ➜  EvaluationSystemServer git:(master) pipenv graph
    Flask-Cors==3.0.7
      - Flask [required: >=0.9, installed: 1.0.2]
        - click [required: >=5.1, installed: 7.0]
        - itsdangerous [required: >=0.24, installed: 1.1.0]
        - Jinja2 [required: >=2.10, installed: 2.10]
          - MarkupSafe [required: >=0.23, installed: 1.1.0]
        - Werkzeug [required: >=0.14, installed: 0.14.1]
      - Six [required: Any, installed: 1.12.0]
    Flask-PyMongo==2.2.0
      - Flask [required: >=0.11, installed: 1.0.2]
        - click [required: >=5.1, installed: 7.0]
        - itsdangerous [required: >=0.24, installed: 1.1.0]
        - Jinja2 [required: >=2.10, installed: 2.10]
          - MarkupSafe [required: >=0.23, installed: 1.1.0]
        - Werkzeug [required: >=0.14, installed: 0.14.1]
      - PyMongo [required: >=3.0, installed: 3.7.2]
    Flask-RESTful==0.3.7
      - aniso8601 [required: >=0.82, installed: 4.0.1]
      - Flask [required: >=0.8, installed: 1.0.2]
        - click [required: >=5.1, installed: 7.0]
        - itsdangerous [required: >=0.24, installed: 1.1.0]
        - Jinja2 [required: >=2.10, installed: 2.10]
          - MarkupSafe [required: >=0.23, installed: 1.1.0]
        - Werkzeug [required: >=0.14, installed: 0.14.1]
      - pytz [required: Any, installed: 2018.7]
      - six [required: >=1.3.0, installed: 1.12.0]
    gevent==1.3.7
      - greenlet [required: >=0.4.14, installed: 0.4.15]
    gunicorn==19.9.0
    python-dotenv==0.10.1
    Flask-PyMongo==2.2.0
    符合要求
    Aggregation Examples — PyMongo 2.7.2 documentation
    “Note
    aggregate requires server version >= 2.1.0. The PyMongo aggregate() helper requires PyMongo version >= 2.3.”
    不清楚到底是否支持了。
    先去试试再说
    python – Aggregate query in mongo works, does not in Pymongo – Stack Overflow
    mongodb – how to find and then aggregate – Stack Overflow
    pymongo and output of aggregate – Stack Overflow
    此处有点诧异：
    为何pymongo有2.7.2和3.7.2，都很新的版本
    但是此处为何只有2.2.0啊
    才想起来：Flask-PyMongo和pymongo 不是同一个吧？
    搜：Flask-PyMongo
    Flask-PyMongo — Flask-PyMongo 2.2.0.post3 documentation
    才注意到是：
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    Flask-PyMongo==2.2.0
    ...
      - PyMongo [required: >=3.0, installed: 3.7.2]
    即：
    • Flask-PyMongo：2.2.0
    • PyMongo：3.7.2
    都是最新的，不用担心版本问题。
    https://flask-pymongo.readthedocs.io/en/latest/
    http://www.pythondoc.com/flask-pymongo/
    没找到aggregate
    用代码：
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    # for debug
    randomPipline = [{ "$sample" : { "size": 1 } }]
    log.debug("randomPipline=%s", randomPipline)
    randomQuestion = questionCollection.aggregate(pipeline=randomPipline)
    log.debug("randomQuestion=%s", randomQuestion)
    randomQuestionType = type(randomQuestion)
    log.debug("randomQuestionType=%s", randomQuestionType)
    得到的是：
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    randomPipline=[{'$sample': {'size': 1}}]
    randomQuestion=<pymongo.command_cursor.CommandCursor object at 0x1082eb320>
    randomQuestionType=<class 'pymongo.command_cursor.CommandCursor'>
    再看看怎么得到record
    参考：
    https://stackoverflow.com/questions/31082323/pymongo-and-output-of-aggregate
    去加上： list()
    https://stackoverflow.com/questions/38133529/aggregate-query-in-mongo-works-does-not-in-pymongo
    “x=db.test.aggregate(aggregation_string)
    print x
    for r in x:
            min_age=r.items()[0]
            print(min_age[1])      #######output:      20”
    【总结】
    最后用代码：
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    randomPipline = [{ "$sample" : { "size": 1 } }]
    log.debug("randomPipline=%s", randomPipline)
    randomQuestionCursor = questionCollection.aggregate(pipeline=randomPipline)
    log.debug("randomQuestionCursor=%s", randomQuestionCursor)
    randomQuestionType = type(randomQuestionCursor)
    log.debug("randomQuestionType=%s", randomQuestionType)
    randomQuestionList = list(randomQuestionCursor)
    log.debug("randomQuestionList=%s", randomQuestionList)
    randomQuestion = randomQuestionList[0]
    log.debug("randomQuestion=%s", randomQuestion)
     
    randomQuestionId = str(randomQuestion["_id"])
    log.debug("randomQuestionId=%s", randomQuestionId)
    randomQuestion.pop("_id")
    log.debug("randomQuestion=%s", randomQuestion)
    randomQuestion["_id"] = randomQuestionId
    log.debug("randomQuestion=%s", randomQuestion)
     
    respDict["message"] = "Get next question ok"
    respDict["data"] = randomQuestion
    return jsonify(respDict)
    可以得到想要的随机出来的单个record：
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    evaluation.py:117 get] randomPipline=[{'$sample': {'size': 1}}]
    evaluation.py:119 get] randomQuestionCursor=<pymongo.command_cursor.CommandCursor object at 0x109e59860>
    evaluation.py:121 get] randomQuestionType=<class 'pymongo.command_cursor.CommandCursor'>
    evaluation.py:123 get] randomQuestionList=[{'_id': ObjectId('5c1777e1cc6df4563adf4aa6'), 'question_number': 88, ..., 'stem_type': 'empty'}]
    evaluation.py:125 get] randomQuestion={'_id': ObjectId('5c1777e1cc6df4563adf4aa6'), 'question_number': 88, ... 'stem_type': 'empty'}
    evaluation.py:128 get] randomQuestionId=5c1777e1cc6df4563adf4aa6
    evaluation.py:130 get] randomQuestion={'question_number': 88, ... 'stem_type': 'empty'}
    evaluation.py:132 get] randomQuestion={'question_number': 88, ... 'stem_type': 'empty', '_id': '5c1777e1cc6df4563adf4aa6'}
    postman测试的flask的接口返回结果效果

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