格式化MongoDB的結果

Question

的MongoDB返回以下JSON數組時，我們取從集合「公司章程」的數據

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

但是我想JSON在以下格式

[{ 
    "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" 
    } 
}] 

是否有可能用獲得這樣的結果MongoDB查詢？

Answer 1

你可以用map reduce做到這一點：

• 地圖功能：

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

• 減少功能：

  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; 
  
  }; 
  

地圖查詢降低：

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

您可以訪問results[0].value.data中的結果。輸出是：

{ 
    "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 
}