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

使用$unwind可以將weekday中的每個數據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.

實例講解:

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

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

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