[DataContract]
    public class User
    {
        [Key]
        [DataMember]
        public String Username { get; set; }

        [DataMember]
        public String Password { get; set; }

        [DataMember]
        public Role Role { get; set; }

        [DataMember]
        public String ValidationToken { get; set; }

        [DataMember]
        public List<OptimizationTask> OptimizationTasks { get; set; }

        public User(String Username=null, String Password=null, Role Role=Role.USER)
        {
            if(Username != null)
            this.Username = Username;

            if(Password != null)
            this.Password = Password;

            if (!Role.Equals(Role.USER))
                this.Role = Role;
        }
    }