How do you find a MongoDB record that is two level deep?

To find a MongoDB record that is two level deep, loop inside MongoDB $where. Let us create a collection with documents −

> db.demo468.insertOne(
... {
... "_id" : new ObjectId(),
... "FirstPosition" : {
...    "StudentName" : "Chris",
...    "StudentAge" : 23
... },
... "SecondPosition" : {
...    "StudentName" : "David",
...    "StudentAge" : 20
... }
... }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e804e2fb0f3fa88e2279069")
}
> db.demo468.insertOne(
... {
... "_id" : new ObjectId(),
... "FirstPosition" : {
...    "StudentName" : "Carol",
...    "StudentAge" : 21
... },
... "SecondPosition" : {
...    "StudentName" : "John",
...    "StudentAge" : 22
... }
... }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e804fb0b0f3fa88e227906a")
}

Display all documents from a collection with the help of find() method −

> db.demo468.find();

This will produce the following output −

{ "_id" : ObjectId("5e804e2fb0f3fa88e2279069"), "FirstPosition" : { "StudentName" : "Chris",
"StudentAge" : 23 }, "SecondPosition" : { "StudentName" : "David", "StudentAge" : 20 } }
{ "_id" : ObjectId("5e804fb0b0f3fa88e227906a"), "FirstPosition" : { "StudentName" : "Carol",
"StudentAge" : 21 }, "SecondPosition" : { "StudentName" : "John", "StudentAge" : 22 } }

Following is the query to find a MongoDB record that is two level deep −

> db.demo468.find({
... $where: function() {
...    for (var i in this) {
...       if (this[i]["StudentName"] == "John") {
...          return true;
...       }
...    }
...    return false;
... }
... })

This will produce the following output −

{ "_id" : ObjectId("5e804fb0b0f3fa88e227906a"), "FirstPosition" : { "StudentName" : "Carol",
"StudentAge" : 21 }, "SecondPosition" : { "StudentName" : "John", "StudentAge" : 22 } }