MongoDB的使用过滤器

Question

在下面的记录我想item_details其中类型是“系统”和id获取子文件中的记录是“7634e9639f5c25f2434b72d8a”

var operator = { 
     'item_details': { 
      $elemMatch: { 
       type: 'custom' 
      } 
     }   
    } 

    var query = { 
    _id : "7634e9639f5c25f2434b72d8a" 
    }; 

    req.db.collection('products').find(query, operator).toArray(function (err, result) { 

    if(err)throw err; 
    console.log(result); 
}); 

它是只返回的第一个元素。但需要获取与查询和投影相匹配的所有记录。 下面是我想要查询的示例数据。

 [ 
     { 

      "_id": "7634e9639f5c25f2434b72d8a", 
      "item_details": [ 
       { 

        "quantity": 1, 
        "sub_total": 1201, 
        "type": "system" 
       }, 
       { 
        "quantity": 19, 
        "sub_total": 140, 
        "type": "custom" 

       }, 
       { 
        "quantity": 81, 
        "sub_total": 130, 
        "type": "custom" 

       }, 
       { 
        "quantity": 71, 
        "sub_total": 90, 
        "type": "system" 

       } 
      ] 

     }, 

     { 

      "_id": "564e9639f5c25f2434b72d8a", 
      "item_details": [ 
       { 

        "quantity": 1, 
        "sub_total": 101, 
        "type": "system" 
       }, 
       { 
        "quantity": 9, 
        "sub_total": 40, 
        "type": "custom" 

       }, 
       { 
        "quantity": 8, 
        "sub_total": 30, 
        "type": "custom" 

       }, 
       { 
        "quantity": 7, 
        "sub_total": 60, 
        "type": "system" 

       } 
      ] 

     } 
    ] 

Answer 1

elemmatch $只会给你数组的第1个要素（子文档）。 见下面 http://docs.mongodb.org/manual/reference/operator/projection/elemMatch/

所以我们宁可用点符号来得到你想要的。

req.db.collection('products').find({"_id": "7634e9639f5c25f2434b72d8a", "item_details.type": "custom"}).toArray(function(err, result) { 
    if (err) throw err; 
    console.log(result); 
});