MongoDB中数组元素的插入顺序答案

【问题标题】：Insertion order of array elements in MongoDBMongoDB中数组元素的插入顺序
【发布时间】：2014-12-16 04:14:25
【问题描述】：

我无法将批量插入的插入顺序保存到 mongodb。

我的应用程序需要连续（通过 HTTP POST @ 每秒一次）将数据发布到服务器。在服务器端，处理 HTTP POST，并将此数据存储在 mongodb v2.4 中的上限集合中。这个上限集合的大小很大 (50MB)。此数据的格式为 JSON，其中包含如下数组：

{"Data":[{"Timestamp":"2014-08-02 13:38:18:852","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0021321268286556005,"b":-0.0010663296561688185}],"Monkec":[{"a":17.511783599853516,"c":-0.42092469334602356,"b":-0.42092469334602356}]},{"Timestamp":"2014-08-02 13:38:18:858","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.892329216003418,"c":-0.2339634746313095,"b":-0.2342628538608551}]},{"Timestamp":"2014-08-02 13:38:18:863","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0021321268286556005,"b":0.0021315941121429205}],"Monkec":[{"a":9.702523231506348,"c":-0.24264541268348694,"b":-0.2148033082485199}]},{"Timestamp":"2014-08-02 13:38:18:866","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.665101051330566,"c":-0.23366409540176392,"b":-0.2197430431842804}]},{"Timestamp":"2014-08-02 13:38:18:868","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.693991661071777,"c":-0.2936892807483673,"b":-0.22857467830181122}]},{"Timestamp":"2014-08-02 13:38:18:872","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.684710502624512,"c":-0.2296224981546402,"b":-0.13786330819129944}]},{"Timestamp":"2014-08-02 13:38:18:873","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.67707633972168,"c":-0.31255003809928894,"b":-0.1902543604373932}]},{"Timestamp":"2014-08-02 13:38:18:875","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0}],"Monkec":[{"a":9.739496231079102,"c":-0.1899549812078476,"b":-0.18845809996128082}]},{"Timestamp":"2014-08-02 13:38:18:878","Rabbit":[{"a":-0.003197923768311739,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.721234321594238,"c":-0.19205063581466675,"b":-0.17318984866142273}]},{"Timestamp":"2014-08-02 13:38:18:881","Rabbit":[{"a":-0.003197923768311739,"c":-0.003197923768311739,"b":0.0010657970560714602}],"Monkec":[{"a":9.78545093536377,"c":-0.2501298487186432,"b":-0.1953437775373459}]},{"Timestamp":"2014-08-02 13:38:18:882","Rabbit":[{"a":0,"c":-0.0010663296561688185,"b":0.0021315941121429205}],"Monkec":[{"a":9.686058044433594,"c":-0.21630020439624786,"b":-0.18247054517269135}]},{"Timestamp":"2014-08-02 13:38:18:884","Rabbit":[{"a":-0.0010663296561688185,"c":0,"b":0.0010657970560714602}],"Monkec":[{"a":9.67198657989502,"c":-0.18546432256698608,"b":-0.23156845569610596}]},{"Timestamp":"2014-08-02 13:38:18:887","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.640103340148926,"c":-0.23276595771312714,"b":-0.25686585903167725}]},{"Timestamp":"2014-08-02 13:38:18:889","Rabbit":[{"a":-0.0010663296561688185,"c":0,"b":0}],"Monkec":[{"a":9.739346504211426,"c":-0.19130218029022217,"b":-0.22602996230125427}]},{"Timestamp":"2014-08-02 13:38:18:891","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0}],"Monkec":[{"a":9.716594696044922,"c":-0.22543121874332428,"b":-0.19728973507881165}]},{"Timestamp":"2014-08-02 13:38:18:898","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.682914733886719,"c":-0.28680360317230225,"b":-0.1740879863500595}]},{"Timestamp":"2014-08-02 13:38:18:904","Rabbit":[{"a":-0.0010663296561688185,"c":0,"b":0.0021315941121429205}],"Monkec":[{"a":9.693093299865723,"c":-0.20866607129573822,"b":-0.2586621046066284}]},{"Timestamp":"2014-08-02 13:38:18:907","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0}],"Monkec":[{"a":9.690997123718262,"c":-0.18681152164936066,"b":-0.23216719925403595}]},{"Timestamp":"2014-08-02 13:38:18:910","Rabbit":[{"a":-0.003197923768311739,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.671688079833984,"c":-0.15388000011444092,"b":-0.2588118016719818}]},{"Timestamp":"2014-08-02 13:38:19:055","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0010663296561688185,"b":0}],"Monkec":[{"a":9.689650535583496,"c":-0.23605911433696747,"b":-0.1989363133907318}]}],"Serial":"35689"}

我正在使用批量插入命令将其插入 mongodb（使用 NodeJs MongoClient 驱动程序）：

    var length = 20; // only doing 20 inserts for testing purposes
    for (var i = 0; i <length;i++) {        
    var bulk = col.initializeUnorderedBulkOp();
    bulk.insert(data["Data"][i]); // data is my JSON data of interest

    bulk.execute(function(err) {
    if (err) {
      return cb(err);
    }

    if (++inserted == length) {
       cb(); // callback (not seen in this code snippet)
    }
  }); // end function
  } // end of for loop

但是，当我检查数据库中的条目时，它们并没有按照数据在原始 JSON 数组中的顺序插入。我的源数据是按时间戳升序排列的，但是 mongodb 上限集合中的一些条目是乱序的。例如，我看到了这个：

{ "Timestamp" : "2014-08-02 13:38:18:910", "Rabbit" : [     {   "a" : -0.003197923768311739,    "c" : -0.0010663296561688185,   "b" : 0.0010657970560714602 } ], "Monkec" : [   {   "a" : 9.671688079833984,    "c" : -0.15388000011444092,     "b" : -0.2588118016719818 } ], "_id" : ObjectId("548e67a683946a5d25bc6d1a") }

{ "Timestamp" : "2014-08-02 13:38:18:884", "Rabbit" : [  {  "a" : -0.0010663296561688185,  "c" : 0,  "b" : 0.0010657970560714602 } ], "Monkec" : [  {   "a" : 9.67198657989502,     "c" : -0.18546432256698608,     "b" : -0.23156845569610596 } ], "_id" : ObjectId("548e67a683946a5d25bc6d13") }

{ "Timestamp" : "2014-08-02 13:38:18:904", "Rabbit" : [  {  "a" : -0.0010663296561688185,  "c" : 0,  "b" : 0.0021315941121429205 } ], "Monkec" : [  {   "a" : 9.693093299865723,    "c" : -0.20866607129573822,     "b" : -0.2586621046066284 } ], "_id" : ObjectId("548e67a683946a5d25bc6d18") }

所以 Timestamp" : "2014-08-02 13:38:18:910 存储在 "Timestamp" : "2014-08-02 13:38:18:884" 之前，即使它是相反的源 JSON。

如何确保 mongodb 以正确的顺序插入数据？我还尝试了非批量插入（db.col.insert 或 db.col.insertOne），但仍然出现这种不一致。谢谢你

【问题讨论】：

Max 已经发布了针对您的问题的解决方案，但请注意批量操作是 2.6 的一个功能。使用 2.4 时，您的驱动程序可能正在后台执行一些魔法以使界面正常工作

标签： node.js mongodb

【解决方案1】：

如果您的查询不要求任何特定的排序/排序，MongoDB 不保证返回的顺序。

如何插入数据无关紧要。您需要做的是像这样编写 find 查询：

// Sort by ascending timestamp
db.my_collection.find({ ... }).sort({"TimeStamp": 1})

有关排序工作原理的更多信息，请参阅http://docs.mongodb.org/manual/reference/method/cursor.sort/#cursor.sort。

当然，如果您想这样做，将Timestamp 上的索引添加到您的集合中会大大受益（请参阅http://docs.mongodb.org/manual/core/indexes/）。

【讨论】：