db.MoviesCollection.find({genres: {$size: 3}})

Find all generes which has size of 3 elements/documents

db.movieStarts.find({genre: { $all: ["action", "thriller"]}}, {title: 1, genre: 1, _id:0 })

Find all generes having action and thriller element. If $all is not used, it will search for the particular order and which is not what we might want.

db.users.find({ hobbies: { $elemMatch: { title:  'sports', frequency: { $gte:  3 } } } }).pretty()

Find all hobbies with element having sports and frequency Greater than or eqals to 3.