mongoDB实战聚合管道--$unwind

Posted 2022-12-13 陈晓婵

  $unwind：将文档中的某一个数组类型字段拆分成多条，每条包含数组中的一个值。

在做项目的时候碰上了这样的需求:

实例讲解:

    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陈晓婵",
    "address" : "北京朝阳区",
    "weekday" : [ 
        1, 
        2, 
        3, 
        4, 
        5
    ]

对weekday进行拆分:

db.getCollection('chenxiaochantest').aggregate(
 [
  
     $unwind:"$weekday"
  
 ]
)

拆分结果:

/* 1 */

    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陈晓婵",
    "address" : "北京朝阳区",
    "weekday" : 1


/* 2 */

    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陈晓婵",
    "address" : "北京朝阳区",
    "weekday" : 2


/* 3 */

    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陈晓婵",
    "address" : "北京朝阳区",
    "weekday" : 3


/* 4 */

    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陈晓婵",
    "address" : "北京朝阳区",
    "weekday" : 4


/* 5 */

    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陈晓婵",
    "address" : "北京朝阳区",
    "weekday" : 5

使用$unwind可以将weekday中的每个数据都被分解成一个文档,并且除了weekday的值不同外,其他的值都是相同的.

实例讲解:

    "_id" : ObjectId("5951ca15567ebff0d5011fbb"),
    "name" : "陈晓婵",
    "address" : "北京朝阳",
    "lunch" : [ 
        
            "food" : "baozi",
            "fruit" : "taozi"
        , 
        
            "food" : "miaotiao",
            "fruit" : "xigua"
        
    ]

对lunch进行拆分:

db.getCollection('chenxiaochantest2').aggregate(
  [
    
       $unwind:"$lunch"
    
  ]
)

拆分结果:

/* 1 */

    "_id" : ObjectId("5951ca15567ebff0d5011fbb"),
    "name" : "陈晓婵",
    "address" : "北京朝阳",
    "lunch" : 
        "food" : "baozi",
        "fruit" : "taozi"
    


/* 2 */

    "_id" : ObjectId("5951ca15567ebff0d5011fbb"),
    "name" : "陈晓婵",
    "address" : "北京朝阳",
    "lunch" : 
        "food" : "miaotiao",
        "fruit" : "xigua"
    

使用$unwind可以将lunch中的每个数据都被分解成一个文档,并且除了lunch的值不同外,其他的值都是相同的.