For this, use $elemMatch, which is used to query nested objects. Let us create a collection with documents −
> db.demo444.insertOne(
... {
... "Information": [{
... id:1,
... Name:"Chris"
... }]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e78ea87bbc41e36cc3caebf")
}
> db.demo444.insertOne(
... {
... "Information": [{
... id:2,
... Name:"David"
... }]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e78ea87bbc41e36cc3caec0")
}
> db.demo444.insertOne(
... {
... "Information": [{
... id:3,
... Name:"Bob"
... }]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e78ea88bbc41e36cc3caec1")
}Display all documents from a collection with the help of find() method −
> db.demo444.find();
This will produce the following output −
{ "_id" : ObjectId("5e78ea87bbc41e36cc3caebf"), "Information" : [ { "id" : 1, "Name" : "Chris" } ] }
{ "_id" : ObjectId("5e78ea87bbc41e36cc3caec0"), "Information" : [ { "id" : 2, "Name" : "David" } ] }
{ "_id" : ObjectId("5e78ea88bbc41e36cc3caec1"), "Information" : [ { "id" : 3, "Name" : "Bob" } ] }Following is the query to improve queries with multikey index in array −
> db.demo444.find({
... "Information":{
... $elemMatch:{
... id:2,
... Name:"David"
... }
... }
... })This will produce the following output −
{ "_id" : ObjectId("5e78ea87bbc41e36cc3caec0"), "Information" : [ { "id" : 2, "Name" : "David" } ] }