[DotNetDevelopment] UI, BusinessLogic, Interfaces and the Data Access Layer

[Adam]

Hi,

I may have designed something fundamentally flawed....

I have three c# projects - a UI, the Business Logic (BL) and a Data
Access Layer (DAL)

Some pseudo(ish) code to illustrate

DAL is:

class DAL
{
   public interface IDALUser
   {
      string UserId { get; set; }
   }

   public void SaveUser(IDALUser myUser)
   {
      /// Save the user using the properties
      /// If UserId is an empty string then generate ID and INSERT
      /// otherwise UPDATE
   }

   public List<IDALUser> SearchForUser(IDALUser searchUser)
   {
      /// User properties to generate SQL SELECT statement
      /// foreach row in results
      ///    Clone() the supplied object, set its properties from the
DataTable, add it to the return list
   }
}

my Business logic (references DAL project)

class User : IDALUser
{
   public string UserId
   {
      /// get and set
   }

   public void Save()
   {
      DAL.SaveUser(this as IDALUser);
   }

   public List<User> User GetById(string userId)
   {
      List<User> returnList = new List<User>();
      searchUser = new User();
      searchUser.UserId = 1;

      foreach(IDALUser current in DAL.SearchForUser(this as IDALUser)
      {
         returnList.add(current as User);
      }

      return returnList;
}

OK, this works. However....
When some idiot (me) is implementing the UI using the BL, they are
able to set the UserId on the BL object. I would rather this property
were internal as it should only be set by the DAL (it tells me whether
to INSERT or UPDATE). Can I achieve this? Or is this approach just bad
design?

If you got this far, thanks for your time.
Any comments/suggestions/abuse gratefully received

Adam