Question

I want to create maintainable code, but this inheritance situation is causing me problems.

The issue is with my 2nd database helper class named InitUserExtension.

Since UserExtension inherits from User, I have to make sure that I mirror any changes in my InitUser helper to InitUserExtension.

I really don’t like this as its prone to bugs, what’s the solution?

My class definitions:

public class User {     public string Name {get; set; }     public string Age { get; set; } }  public class UserExtension : User {     public string Lastname {get; set; }         public string Password {get; set; }  } 

My database helpers:

public static SqlDataReader InitUser(SqlDataReader dr) {       User user = new User();        user.Name = Convert.ToString(dr['name']);       user.Age ... }   public static SqlDataReader InitUserExtension(SqlDataReader dr) {       UserExtension user = new UserExtension();         // note: mirror attributes from User       user.Name = Convert.ToString(dr['name']);       user.Age ...          user.Lastname = Convert.ToString(dr['lastname']);       user.Password = ....; } 

Answer 1

How about moving the processing of Name etc into a method (accepting either a User or a T : User), and call that from both?

private static void InitUser(User user, SqlDataReader dr) { // could also use an interface here, or generics with T : User   user.Name = Convert.ToString(dr['name']);   user.Age ... }   public static User InitUser(SqlDataReader dr) {     User user = new User();     InitUser(user, dr);     return user; }  public static UserExtension InitUserExtension(SqlDataReader dr) {   UserExtension user = new UserExtension();   InitUser(user, dr);   user.Lastname = Convert.ToString(dr['lastname']);   user.Password = ....;   return user; } 

As an alternative, you could reduce the line count, but increase the complexity, using generics:

private static T InitUserCore<T>(SqlDataReader dr) where T : User, new() {     T user = new T();     // ...     return user; } public static User InitUser(SqlDataReader dr) {     return InitUserCore<User>(dr); } public static UserExtension InitUserExtension(SqlDataReader dr) {     UserExtension user = InitUserCore<UserExtension>(dr);     // ...     return user; }