格式化MongoDB结果

当我们从集合“Articles”获取数据时，MongoDB返回以下JSON数组

但是，我需要以下格式的json

[{
    "id1": {
        "_id": "id1",
        "description": "Description for article",
        "author": "publisher of article"
    },
    "id2": {
        "_id": "id2",
        "description": "Description for article",
        "author": "publisher of article"
    },
    "id3": {
        "_id": "id3",
        "description": "Description for article",
        "author": "publisher of article"
    }
}]

使用MongoDB查询是否可以获得这样的结果？

您可以通过以下方法实现：

• 地图功能：

  var mapFunction = function() {
      var obj = {};
  
      obj[this._id] = {
  
          "_id": this._id,
          "description": this.description,
          "author": this.author
  
      };
      emit(1,obj);
  };
  

  var reduceFunction = function(key, values) {
  
      var reduced = {};
  
      var output_arr = [];
  
      values.forEach(function(value) {
          Object.keys(value).forEach(function(key) {
              var obj = {};
              obj[key]=value[key];
              output_arr.push(obj);
          });
      });
  
      reduced["data"] = output_arr;
  
      return reduced;
  
  };
  

• 减少功能：

  var mapFunction = function() {
      var obj = {};
  
      obj[this._id] = {
  
          "_id": this._id,
          "description": this.description,
          "author": this.author
  
      };
      emit(1,obj);
  };
  

  var reduceFunction = function(key, values) {
  
      var reduced = {};
  
      var output_arr = [];
  
      values.forEach(function(value) {
          Object.keys(value).forEach(function(key) {
              var obj = {};
              obj[key]=value[key];
              output_arr.push(obj);
          });
      });
  
      reduced["data"] = output_arr;
  
      return reduced;
  
  };
  

map reduce查询：

db.items.mapReduce(mapFunction, reduceFunction, { out: { inline: 1 } })

您可以在

结果[0].value.data

中访问结果。输出为：

{
    "results" : [
        {
            "_id" : 1,
            "value" : {
                "data" : [
                    {
                        "id1" : {
                            "_id" : "id1",
                            "description" : "Description for article",
                            "author" : "publisher of article"
                        }
                    },
                    {
                        "id2" : {
                            "_id" : "id2",
                            "description" : "Description for article",
                            "author" : "publisher of article"
                        }
                    },
                    {
                        "id3" : {
                            "_id" : "id3",
                            "description" : "Description for article",
                            "author" : "publisher of article"
                        }
                    }
                ]
            }
        }
    ],
    "timeMillis" : 11,
    "counts" : {
        "input" : 3,
        "emit" : 3,
        "reduce" : 1,
        "output" : 1
    },
    "ok" : 1
}

---

为什么要这样格式化？为了通过指定键直接获取结果，而不是在JSONC中循环，可以使用聚合或项目来完成此操作，因为当我运行此查询以获取大量记录时，需要花费大量时间。现在还没有（mongo 3.4），可能在将来的版本中，请参阅