How to know whether a field contains a string or not in MongoDb?

Question

Is there any operator, which allows me to check, if the value of a field contains a certain string?

Something in this way:

db.users.findOne({$contains:{"username":"son"}})

Answer 1

This can be done by following code:

db.users.findOne({"username" : {$regex : ".*son.*"}});