Question

下面的mongodb数据有问题。我想获取数据[projects][log][subject]。所以，我试过这个

$project':{_id:0, projects.log.subject:1}

但语法不正确..

{
    "_id": ObjectID("569f3a3e9d2540764d8bde59"),
    "A": "book",
    "server": "us",
    "projects": [
        {
            "domainArray": [
                {
                    ~~~~
                }
            ],
            "log": [
                {
                    ~~~~~,
                    "subject": "I WANT THIS"
                }
            ],
            "before": "234234234"
        },
        {
            "domainArray": [
                {
                    ~~~~
                }
            ],
            "log": [
                {
                    ~~~~~,
                    "subject": "I WANT THIS"
                }
            ],
            "before": "234234234"
        },....
    ] //end of projects
}//end of document

如何通过[subject]获取数据分组？我不知道这个......

Edited- 我期待这样的数据

{
"subject":"first",
"subject":"second",
"subject":"third",
"subject":"~~~"
}

有可能吗？我只想获得一系列主题。

Answer 1

不确定这是否是您的预期结果。你可以试试这个：

db.project.aggregate([
            {$project:{projects:1,_id:0}},
            {$unwind:"$projects"},
            {$unwind:"$projects.log"},
            {$project:{subject:"$projects.log.subject",_id:0}}
            ])

对于上面的字数结果，

和Map-Reduce如下：

//map function
var map = function() {

  for(var i in this.projects)
  {
      for(var j in this.projects[i].log)
      {

         var arrayWords = this.projects[i].log[j].subject.split(" ");
         for(var k = 0; k < arrayWords.length; k++)
         {
            emit(arrayWords[k],{occurance:1}); 
         }

      } 

  } 

};

//reduce function
function reduce(word, arrayOccurance) {

  var totalOccurance = 0;

  for (var i = 0; i < arrayOccurance.length; i++) 
  {
    totalOccurance = totalOccurance + arrayOccurance[i].occurance;
  }

  return { occurance:totalOccurance };
}

//combine both function into operation and output result into wordOccurance collection

db.project.mapReduce(
                       map,
                       reduce,
                       {
                          query: {"projects.log.subject":"~~~~~"}, 
                          out: "wordOccurance" 
                       }
                     )

//query the result output

db.wordOccurance.find()

您可以更改mapreduce下的查询，以匹配您想要字数的主题。如果我的mapreduce函数不符合您的预期结果，请告诉我。

您还可以参考以下两页来创建地图和缩小功能并进行故障排除：

Troubleshoot the Map Function

Troubleshoot the Reduce Function

选择数组内部元素

1 个答案: