mongodb $unwind 聚合管道

$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。
需求：

{"_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"}]
)

拆封结果:

/* 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"}
}