How to efficiently perform “distinct” with multiple keys in MongoDB?

You can perform distinct with multiple keys with the help of an aggregate framework.

To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −

> db.distinctWithMultipleKeysDemo.insertOne({"StudentName":"Mike","StudentAge":22,"StudentMathMarks":56});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c7f74488d10a061296a3c53")
}
> db.distinctWithMultipleKeysDemo.insertOne({"StudentName":"Mike","StudentAge":22,"StudentMathMarks":56});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c7f744b8d10a061296a3c54")
}
> db.distinctWithMultipleKeysDemo.insertOne({"StudentName":"Bob","StudentAge":23,"StudentMathMarks":45});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c7f74598d10a061296a3c55")
}
> db.distinctWithMultipleKeysDemo.insertOne({"StudentName":"Bob","StudentAge":23,"StudentMathMarks":45});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c7f745e8d10a061296a3c56")
}
> db.distinctWithMultipleKeysDemo.insertOne({"StudentName":"Carol","StudentAge":27,"StudentMathMarks":54});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c7f74688d10a061296a3c57")
}

Display all documents from a collection with the help of find() method. The query is as follows −

> db.distinctWithMultipleKeysDemo.find().pretty();

The following is the output −

{
   "_id" : ObjectId("5c7f74488d10a061296a3c53"),
   "StudentName" : "Mike",
   "StudentAge" : 22,
   "StudentMathMarks" : 56
}
{
   "_id" : ObjectId("5c7f744b8d10a061296a3c54"),
   "StudentName" : "Mike",
   "StudentAge" : 22,
   "StudentMathMarks" : 56
}
{
   "_id" : ObjectId("5c7f74598d10a061296a3c55"),
   "StudentName" : "Bob",
   "StudentAge" : 23,
   "StudentMathMarks" : 45
}
{
   "_id" : ObjectId("5c7f745e8d10a061296a3c56"),
   "StudentName" : "Bob",
   "StudentAge" : 23,
   "StudentMathMarks" : 45
}
{
   "_id" : ObjectId("5c7f74688d10a061296a3c57"),
   "StudentName" : "Carol",
   "StudentAge" : 27,
   "StudentMathMarks" : 54
}

Here is the query to perform distinct with multiple keys −

> c = db.distinctWithMultipleKeysDemo;
test.distinctWithMultipleKeysDemo
> myResult = c.aggregate( [ {"$group": { "_id": { StudentName:"$StudentName", StudentAge: "$StudentAge" } } } ] );

The following is the output −

{ "_id" : { "StudentName" : "Carol", "StudentAge" : 27 } }
{ "_id" : { "StudentName" : "Bob", "StudentAge" : 23 } }
{ "_id" : { "StudentName" : "Mike", "StudentAge" : 22 } }