向所有的銀行賬戶文檔中加入數組字段 ~~~ db.accounts.update( {"name.firstName":"alice"}, { $set: {currency:["CNY","USD"]} } ) db.accounts.update( {"name.firstName":"bob"}, {$set:{currency:["GBP"]}} ) ~~~ ``` 返回結果 WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 2 }) ``` 將文檔中的貨幣種類數組展開 ~~~ db.accounts.aggregate([ { $unwind:{ path:"$currency" } }]) ~~~ 返回數據： ``` { "_id" : ObjectId("60d2cb85c9b0d831c97763ea"), "name" : { "firstName" : "alice", "lastName" : "wong" }, "balance" : 50, "currency" : "CNY" } { "_id" : ObjectId("60d2cb85c9b0d831c97763ea"), "name" : { "firstName" : "alice", "lastName" : "wong" }, "balance" : 50, "currency" : "USD" } { "_id" : ObjectId("60d2cb85c9b0d831c97763eb"), "name" : { "firstName" : "bob", "lastName" : "yang" }, "balance" : 20, "currency" : "GBP" } ```