To apply a condition, use $setIsSubset. Let us first create a collection with documents −
> db.subsetDemo.insertOne({"StudentName":"Chris","StudentFavouriteSubject":["Java","Python"]}); { "acknowledged" : true, "insertedId" : ObjectId("5e063e49150ee0e76c06a052") } > db.subsetDemo.insertOne({"StudentName":"Chris","StudentFavouriteSubject":["Java","Python","MySQL"]}); { "acknowledged" : true, "insertedId" : ObjectId("5e063e4f150ee0e76c06a053") }
Following is the query to display all documents from a collection with the help of find() method −
> db.subsetDemo.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5e063e49150ee0e76c06a052"), "StudentName" : "Chris", "StudentFavouriteSubject" : [ "Java", "Python" ] } { "_id" : ObjectId("5e063e4f150ee0e76c06a053"), "StudentName" : "Chris", "StudentFavouriteSubject" : [ "Java", "Python", "MySQL" ] }
Here is the query to apply condition inside subset in MongoDB aggregation −
> db.subsetDemo.aggregate([ ... { ... $project: { ... _id: 0, ... StudentName: 1, ... isMySQL: { ... $setIsSubset: [["MySQL"], "$StudentFavouriteSubject"] ... } ... } ... } ... ]);
This will produce the following output −
{ "StudentName" : "Chris", "isMySQL" : false } { "StudentName" : "Chris", "isMySQL" : true }