从子文档返回字段数组

Question

请任何人帮助我查询mongo以展开数组，并且我正在使用mongdb本机驱动程序我的收集文档如下所示，也请忽略我的objectId i只是作为示例

{  
      "_id":ObjectId(123),
      "name":"Sam",
      "age":20,
      "hobbiesDetail":[  
         {  
            "description":"FootBall",
            "level":"20%"
         },
         {  
            "description":"Cricket",
            "level":"80%"
         }
      ]
   },
   {  
      "_id":ObjectId(124),
      "name":"Ted",
      "age":26,
      "hobbiesDetail":[  
         {  
            "description":"FootBall",
            "level":"20%"
         }
      ]
   }

我的预期产出是

[  
   {  
      "name":"Sam",
      "age":20,
      "hobbies":"Football,Cricket"
   },
   {  
      "name":"Ted",
      "age":26,
      "hobbies":"Football"
   }
]

我只想在一个查询Thanx中展开我的数组并在兴趣爱好描述之间添加一个逗号，以获得任何帮助。

Answer 1

您所需要的只是一个带有$project数组运算符的$map离子。

db.collection.aggregate([
    { "$project": { 
        "name": 1, 
        "age": 1, 
        "hobbies": { 
            "$map": { 
                "input": "$hobbiesDetail", 
                "as": "hobby", 
                "in": "$$hobby.description" 
            } 
        } 
    }}
])