MongoDB 聚合：创建子文档

Question

我有一个 MongoDB 集合，其中包含如下文档：

{
  "_id": ObjectId("..."),
  "code": 22726,
  "parent_code": 35481,
  "parent_description": "posterdati",
},
{
  "_id": ObjectId("..."),
  "code": 22726,
  "parent_code": 35484,
  "parent_description": "vicesindaco",
},
{
  "_id": ObjectId("..."),
  "code": 22727,
  "parent_code": 35487,
  "parent_description": "prefettura",
}

我想使用 "code" 字段作为 _id 对它们进行 $group，创建一个包含 parent_code 和 parent_description:

的子文档数组

{
    "code": 22726,
    parents: [
        {
            "parent_code": 35481,
            "parent_description": "posterdati"
        },
        {
            "parent_code": 35484,
            "parent_description": "vicesindaco"
        }
    ]
},
{
    "code": 22727,
    parents: [
        {
            "parent_code": 35487,
            "parent_description": "prefettura"
        }
    ]
}

是否可以仅使用聚合框架？我在聚合框架文档中没有看到对子文档的引用，所以我认为不是...

谢谢大家。

Answer 1

您可以使用以下聚合管道来获得所需的结果：

db.collection.aggregate([
    {
        "$group": {
            "_id": "$code",
            "parents": {
                "$addToSet": {
                    "parent_code": "$parent_code",
                    "parent_description": "$parent_description"
                }
            }
        }
    },
    {
        "$project": {
            "_id": 0,
            "code": "$_id",
            "parents": 1
        }
    }
]);

输出:

/* 0 */
{
    "result" : [ 
        {
            "parents" : [ 
                {
                    "parent_code" : 35487,
                    "parent_description" : "prefettura"
                }
            ],
            "code" : 22727
        }, 
        {
            "parents" : [ 
                {
                    "parent_code" : 35484,
                    "parent_description" : "vicesindaco"
                }, 
                {
                    "parent_code" : 35481,
                    "parent_description" : "posterdati"
                }
            ],
            "code" : 22726
        }
    ],
    "ok" : 1
}

MongoDB 聚合：创建子文档

MongoDB Aggregation: creating subdocuments

mongodb

mongodb-query

aggregation-framework