如何仅显示嵌套 MongoDB 文档中的键?
mongodbdatabasebig data analytics
让我们创建一个包含文档的集合 −
> db.demo740.insertOne({
... "details":
... [
... {
... Name:"Chris",
... Age:21,
... CountryName:"US"
... },
... {
... Name:"Bob",
... Age:20,
... CountryName:"UK",
... isMarried:true
... }
... ]
... });
{
"acknowledged" : true,
"insertedId" : ObjectId("5ead700c57bb72a10bcf066d")
}
借助 find() 方法显示集合中的所有文档 −
> db.demo740.find();
这将产生以下输出 −
"_id" : ObjectId("5ead700c57bb72a10bcf066d"), "details" : [ { "Name" : "Chris", "Age" : 21, "CountryName" : "US" }, { "Name" : "Bob", "Age" : 20, "CountryName" : "UK", "isMarried" : true } ] }
以下是获取嵌套 MongoDB 文档的键的查询 −
> db.demo740.aggregate([
... {
... $project: {
... ListKeys: {
... $reduce: {
... input: "$details",
... initialValue: [],
... in: {
... $concatArrays: [
... "$$value",
... {
... $map: {
... input: {
... $objectToArray: "$$this"
... },
... in: "$$this.k"
... }
... }
... ]
... }
... }
... }
... }
... }
... ]).pretty()
这将产生以下输出 −
{
"_id" : ObjectId("5ead700c57bb72a10bcf066d"),
"ListKeys" : [
"Name",
"Age",
"CountryName",
"Name",
"Age",
"CountryName",
"isMarried"
]
}
