如何更改 Mongo 文档中嵌套字段的数据类型? [英] How to change datatype of nested field in Mongo document?

问题描述

我的 Mongo 结构如下，

My Mongo structure as below,

"topProcesses" : [
        {
            "cpuUtilizationPercent" : "0.0",
            "processId" : "1",
            "memoryUtilizationPercent" : "0.1",
            "command" : "init",
            "user" : "root"
        },
        {
            "cpuUtilizationPercent" : "0.0",
            "processId" : "2",
            "memoryUtilizationPercent" : "0.0",
            "command" : "kthreadd",
            "user" : "root"
        },
        {
            "cpuUtilizationPercent" : "0.0",
            "processId" : "3",
            "memoryUtilizationPercent" : "0.0",
            "command" : "ksoftirqd/0",
            "user" : "root"
        },
        {
            "cpuUtilizationPercent" : "0.0",
            "processId" : "5",
            "memoryUtilizationPercent" : "0.0",
            "command" : "kworker/0:+",
            "user" : "root"
        },
        {
            "cpuUtilizationPercent" : "0.0",
            "processId" : "6",
            "memoryUtilizationPercent" : "0.0",
            "command" : "kworker/u3+",
            "user" : "root"
        },
        {
            "cpuUtilizationPercent" : "0.0",
            "processId" : "8",
            "memoryUtilizationPercent" : "0.0",
            "command" : "rcu_sched",
            "user" : "root"
        } 
    ]

现在在上面的文档中 topProcesses.cpuUtilizationPercent 是字符串，我想将 topProcesses.cpuUtilizationPercent 数据类型更改为 Float.为此，我在下面尝试过，但没有用

Now in above documents topProcesses.cpuUtilizationPercent is in string and I wanted to change topProcesses.cpuUtilizationPercent data type to Float. For this I tried below but it did not work

db.collectionName.find({
   "topProcesses":{"$exists":true}}).forEach(function(data){
    for(var ii=0;ii<data.topProcesses.length;ii++){
   db.collectionName.update({_id: data._id},{$set:{"topProcesses.$.cpuUtilizationPercent":parseFloat(data.topProcesses[ii].cpuUtilizationPercent)}},false,true);
  }
})

任何人都可以帮助如何将字符串更改为在嵌套的 Mongo 文档中浮动

Can any one help how to changed string to float in nested Mongo documents

推荐答案

您以正确的方式执行此操作，但是您没有在 .update() 的查询部分中包含要匹配的数组元素:

You are doing this the right way but you did not include the array element to match in the query portion of the .update():

db.collectionName.find({
   "topProcesses":{"$exists":true}}).forEach(function(data){
    for(var ii=0;ii<data.topProcesses.length;ii++) {
      db.collectionName.update(
         { 
             "_id": data._id, 
             "topProcesses.processId": data.topProcesses[ii].processId // corrected
         },
         {
             "$set": {
               "topProcesses.$.cpuUtilizationPercent":
                   parseFloat(data.topProcesses[ii].cpuUtilizationPercent)
             }
         }
      );
  }
})

因此您需要匹配数组中的某些内容，以便 positional $ 操作符有什么作用.

So you need to match something in the array in order for the positional $ operator to have any effect.

您也可以在表示法中使用索引"值，因为无论如何您都是在循环中生成的:

You also could have just used the "index" value in the notation, since you are producing that in a loop anyway:

db.collectionName.find({
   "topProcesses":{"$exists":true}}).forEach(function(data){
    for(var ii=0;ii<data.topProcesses.length;ii++) {

      var updoc =  { 
          "$set": {}
      };

      var myKey = "topProcesses." + ii + ".cpuUtilizationPercent";
      updoc["$set"][myKey] = parseFloat(data.topProcesses[ii].cpuUtilizationPercent);

      db.collectionName.update(
         { 
             "_id": data._id
         },
         updoc
      );
  }
})

它只使用匹配的索引，并且在没有数组元素的唯一标识符的情况下很方便.

Which just uses the matching index and is handy where there is no unique identifier of the array element.

另请注意，由于处理现有文档的方式的性质，此处不应应用upsert"或multi"选项.

Also note that neither the "upsert" or "multi" options should apply here due to the nature of how this is processes existing documents.

作为对此的后记"说明，在 2.6 及更高版本中考虑 MongoDB 的批量操作 API 也是值得的.使用这些 API 方法，您可以显着减少客户端应用程序和数据库之间的网络流量.这里明显的改进是整体速度:

Just as a "postscript" note to this, it is also worthwhile to consider the Bulk Operations API of MongoDB in versions from 2.6 and greater. Using these API methods you can significantly reduce the amount of network traffic between your client application and the database. The obvious improvement here is in the overall speed:

var bulk = db.collectionName.initializeOrderedBulkOp();
var counter = 0;

db.collectionName.find({
   "topProcesses":{"$exists":true}}
).forEach(function(data){
    for(var ii=0;ii<data.topProcesses.length;ii++) {

      var updoc =  { 
          "$set": {}
      };

      var myKey = "topProcesses." + ii + ".cpuUtilizationPercent";
      updoc["$set"][myKey] = parseFloat(data.topProcesses[ii].cpuUtilizationPercent);

      // queue the update
      bulk.find({ "_id": data._id }).update(updoc);
      counter++;

      // Drain and re-initialize every 1000 update statements
      if ( counter % 1000 == 0 ) {
          bulk.execute();
          bulk = db.collectionName.initializeOrderedBulkOp();
      }
  }
})

// Add the rest in the queue
if ( counter % 1000 != 0 )
    bulk.execute();

这基本上将发送到服务器的操作语句数量减少到每 1000 个排队操作仅发送一次.您可以使用该数字以及事物的分组方式，但它会以相对安全的方式显着提高速度.

This basically reduces the amount of operations statements sent to the sever to only sending once every 1000 queued operations. You can play with that number and how things are grouped but it will give a significant increase in speed in a relatively safe way.

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