node.js – Mongodb使用过滤器获取子文档中的记录

在以下记录中我想得到item_details类型为“system”且id为“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);
});

它只返回第一个元素.但需要获取与查询和投影匹配的所有记录.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"

                }
            ]

        }
    ]

$elemmatch只会给你数组的第一个元素(在子文档中).
见下文
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东西.

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