[{_id:"chrYMAqT8meXpqdrC",message:"Hello world. This is mongo"},{_id:"rKu5gf5zL6NaSvZ5Q",message:"hello. This is mongo world"},{_id:"rKu5gf5zL6NaSvZ5R",message:"world. This is mongo Hello"}]

db.collection.find({message:{$regex:"Hello.*world",$options:"i"}})