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How to display only the keys from nested MongoDB documents?
Let us create a collection with documents −
> db.demo740.insertOne({
... "details":
... [
... {
... Name:"Chris",
... Age:21,
... CountryName:"US"
... },
... {
... Name:"Bob",
... Age:20,
... CountryName:"UK",
... isMarried:true
... }
... ]
... });
{
"acknowledged" : true,
"insertedId" : ObjectId("5ead700c57bb72a10bcf066d")
}Display all documents from a collection with the help of find() method −
> db.demo740.find();
This will produce the following output −
"_id" : ObjectId("5ead700c57bb72a10bcf066d"), "details" : [ { "Name" : "Chris", "Age" : 21, "CountryName" : "US" }, { "Name" : "Bob", "Age" : 20, "CountryName" : "UK", "isMarried" : true } ] }Following is the query to get keys of nested MongoDB documents −
> db.demo740.aggregate([
... {
... $project: {
... ListKeys: {
... $reduce: {
... input: "$details",
... initialValue: [],
... in: {
... $concatArrays: [
... "$$value",
... {
... $map: {
... input: {
... $objectToArray: "$$this"
... },
... in: "$$this.k"
... }
... }
... ]
... }
... }
... }
... }
... }
... ]).pretty()This will produce the following output −
{
"_id" : ObjectId("5ead700c57bb72a10bcf066d"),
"ListKeys" : [
"Name",
"Age",
"CountryName",
"Name",
"Age",
"CountryName",
"isMarried"
]
}
Updated on: 30-Jun-2020
399 Views
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