【mongoDB实战】聚合管道--$unwind

我不是女神ヾ 2022-06-13 04:20 251阅读 0赞

**  $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.**