Database
[{"UserId":"1","IsAndroid":true,"IsIos":false,"IsWeb":false},{"UserId":"2","IsAndroid":false,"IsIos":true,"IsWeb":false},{"UserId":"3","IsAndroid":false,"IsIos":false,"IsWeb":true}]
Query
db.collection.aggregate([{$addFields:{Combo:{$switch:{branches:[{case:"$IsAndroid",then:"ANDROID"},{case:"$IsIos",then:"IOS"},{case:"$IsWeb",then:"WEB"}],default:"Unknown"}}}}])