mongodb $unwind 聚合管道

$unwind

：将文檔中的某一個數組類型字段拆分成多條，每條包含數組中的一個值。

需求：

{
    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陳曉婵",
    "address" : "北京朝陽區",
    "weekday" : [ 
        1, 
        2, 
        3, 
        4, 
        5
    ]
}
           

對weekday進行拆分:

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

拆分結果:

/* 1 */
{
    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陳曉婵",
    "address" : "北京朝陽區",
    "weekday" : 1
}
 
/* 2 */
{
    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陳曉婵",
    "address" : "北京朝陽區",
    "weekday" : 2
}
 
/* 3 */
{
    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陳曉婵",
    "address" : "北京朝陽區",
    "weekday" : 3
}
 
/* 4 */
{
    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陳曉婵",
    "address" : "北京朝陽區",
    "weekday" : 4
}
 
/* 5 */
{
    "_id" : ObjectId("5951c5de567ebff0d5011fba"),
    "name" : "陳曉婵",
    "address" : "北京朝陽區",
    "weekday" : 5
}
           

使用$unwind可以将weekday中的每個資料都被分解成一個文檔,并且除了weekday的值不同外,其他的值都是相同的.

執行個體講解:

{
    "_id" : ObjectId("5951ca15567ebff0d5011fbb"),
    "name" : "陳曉婵",
    "address" : "北京朝陽",
    "lunch" : [ 
        {
            "food" : "baozi",
            "fruit" : "taozi"
        }, 
        {
            "food" : "miaotiao",
            "fruit" : "xigua"
        }
    ]
}
           

對lunch進行拆分:

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

拆封結果:

/* 1 */
{
    "_id" : ObjectId("5951ca15567ebff0d5011fbb"),
    "name" : "陳曉婵",
    "address" : "北京朝陽",
    "lunch" : {
        "food" : "baozi",
        "fruit" : "taozi"
    }
}
 
/* 2 */
{
    "_id" : ObjectId("5951ca15567ebff0d5011fbb"),
    "name" : "陳曉婵",
    "address" : "北京朝陽",
    "lunch" : {
        "food" : "miaotiao",
        "fruit" : "xigua"
    }
}
           

轉載來源：https://blog.csdn.net/chenxiaochan/article/details/73771879