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Legal Studies如何僅使用 MongoDB 聚合獲取陣列中的值？
讓我們建立一個包含文件的集合——
> db.demo411.insertOne(
... {
... "Information" : [
... {
... "Name1" : "Chris",
... "Name2" : "David"
... },
... {
... "Name1" : "John",
... "Name2" : "John"
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e70f19715dc524f70227682")
}藉助 find() 方法顯示集合中的所有文件——
> db.demo411.find();
這將生成以下輸出——
{ "_id" : ObjectId("5e70f19715dc524f70227682"), "Information" : [ { "Name1" : "Chris", "Name2" : "David" }, { "Name1" : "John", "Name2" : "John" } ] }以下是僅獲取陣列中值所用的查詢——
> db.demo411.aggregate(
... [
... {$project : {
... _id : 0,
... Information : {$map : {input : "$Information", as : "out", in : ["$$out.Name1", "$$out.Name2"]}}
... }
... }
... ]
... )這將生成以下輸出——
{ "Information" : [ [ "Chris", "David" ], [ "John", "John" ] ] }
更新於： 03-04-2020
848 次瀏覽
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