如何获取嵌入文档中的单个字段? [英] How to get individual fields in embedded documents?

问题描述

假设我有一个像下面这样的文档

Lets say i have a document like following

{
"_id" : 1,
"name" : "sue",
"age" : 19,
"type" : 1,
"status" : "P",
"favorites" : {
    "artist" : "Picasso",
    "food" : "pizza"
},
"finished" : [
    17,
    3
],
"badges" : [
    "blue",
    "black"
],
"points" : [
    {
        "points" : 85,
        "bonus" : 20
    },
    {
        "points" : 85,
        "bonus" : 10
    }
]

}

当我运行像 db.users.find( { 收藏夹:{ 艺术家:毕加索"，食物:比萨"}}，{最喜欢的食物":1 } ).pretty()

我得到以下结果

{ "_id" : 1, "favorites" : { "food" : "pizza" } }

是否可以只获取 food 字段，如

Is it possible to get only food field like

{食物":披萨"}

没有收藏夹键?

推荐答案

您可以通过 $project

you can achieve this using aggregation with $project

db.users.aggregate([  
   {  
      $match:{  
         favorites:{  
            artist:"Picasso",
            food:"pizza"
         }
      }
   },
   {  
      $project:{  
         _id:0,
         food:"$favorites.food"
      }
   }
])

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