Question

In many projects I have to make a table containing users and implementing standard user-based functions such as authentication, saving, etc. So I decided to make a class library containing these functionalities, for example:

public class User
{
  public int? Id {get;set;}
  public string UserName {get;set;}
  public string Password {get;set;}
}

public class MyDbContext : DbContext
{
  public DbSet<User> {get;set;}
}

public class UserService
{
  public MyDbContext Context {get;set;} // will be initialized in constructor

  public User GetByUserName(string username)
  {
    return (from s in Context.Users where s.UserName.Equals(username) select s).SingleOrDefault();
  }

  // etc...
}

Now when I start a new Mvc project I add this library and extends the DbContext with custom models. The problem is I don’t know how to extend the User table with some additional fields, for example:

public class MyUser : User
{
   public bool IsApproved {get;set;}
}

public class CustomDbContext : MyDbContext
{
  public DbSet<SomeOtherModel> {get;set;}

  // problem: override DbSet in MyDbContext with class MyUser?
  //public DbSet<MyUser> {get;set;}
}

In this case I also need to override the DbSet<User> of the MyDbContext. If I remove the DbSet<User> in the library my UserService class won’t work anymore. Any ideas how to make an extensible framework?

Answer 1

You could use generics (I haven’t tested this, just a thought):

public abstract class UserDbContext<TUser> : DbContext where TUser : User
{
  public DbSet<TUser> Users {get;set;}
}

And then inherit:

public class CustomDbContext : MyDbContext<MyUser>

And the same generic in the UserService:

public abstract class UserService<TUser> where TUser : User
{
  public UserDbContext<TUser> Context {get;set;} // will be initialized in constructor

  public TUser GetByUserName(string username)
  {
    return (from s in Context.Users where s.UserName.Equals(username) select s).SingleOrDefault();
  }

  // etc...
}