object DatabaseConnection {
    private val Connection = ...

    private object PasswordDevice {
        def check(pw1: String, pw2: String) = ...
        def encrypt(password: String) = ...
    }

    object LoginDevice {
        private val GetUserStatement = Connection.prepareStatement("SELECT Name, Password, ... FROM Users WHERE UPPER(Name) = UPPER(?)")

        def login(username: String, password: String) = {
            GetUserStatement.setString(1, username)
            val userResult = GetUserStatement.executeQuery
            if ( !userResult.next )
                throw User.NotFoundException
            if ( !PasswordDevice.check(password, userResult.getString("Password")) )
                throw User.WrongPasswordException
            new User(userResult.getString("Name"), ...)
        }
    }


    object RegisterDevice {
        private val RegisterStatement = Connection.prepareStatement("SELECT Name, Password, ... FROM Users WHERE UPPER(Name) = UPPER(?)")
        private val GetKeyStatement = Connection.prepareStatement("SELECT Key FROM Keys WHERE Key = ?")
        private val InsertStatement = Connection.prepareStatement(s"INSERT INTO Users VALUES(?, ?, ...)")
        private val DeleteKeyStatement = Connection.prepareStatement("DELETE FROM Keys WHERE Key = ?")

        def register(name: String, password: String, key: String) = {
            RegisterStatement.setString(1, name)
            GetKeyStatement.setString(1, key)
            val userExistsResult = RegisterStatement.executeQuery
            val keyValidResult = GetKeyStatement.executeQuery
            if ( userExistsResult.next ) throw User.AlreadyExistsException
            if ( !keyValidResult.next ) throw User.InvalidKeyException
            InsertStatement.setString(1, name)
            InsertStatement.setString(2, PasswordDevice.encrypt(password))
            InsertStatement.executeUpdate()
            DeleteKeyStatement.setString(1, key)
            DeleteKeyStatement.executeUpdate()
            new User(name, ...)
        }
    }

    object RequestDevice {
        private val RequestStatement = Connection.prepareStatement("SELECT Request.* FROM Request WHERE ID = ?")

        def request(id: String) = {
            RequestStatement.setString(1, id)
            val result = RequestStatement.executeQuery
            if(!result.next)
                throw Request.InvalidIDException
            new DataElement(result.getString("ID"), ...)
        }
    }

    ...
}