Question

Is it possible to extend LINQ-to-SQL entity-classes with constructor-methods and in the same go; make that entity-class inherit from it’s data-context class?–In essence converting the entity-class into a business object.

This is the pattern I am currently using:

namespace Xxx {     public class User : Xxx.DataContext     {         public enum SiteAccessRights         {             NotRegistered = 0,             Registered = 1,             Administrator = 3         }          private Xxx.Entities.User _user;          public Int32 ID         {             get             {                 return this._user.UsersID;             }         }          public Xxx.User.SiteAccessRights AccessRights         {             get             {                 return (Xxx.User.SiteAccessRights)this._user.UsersAccessRights;             }              set             {                 this._user.UsersAccessRights = (Int32)value;             }         }          public String Alias         {             get             {                 return this._user.UsersAlias;             }              set             {                 this._user.UsersAlias = value;             }         }           public User(Int32 userID)         {             var user = (from u in base.Users                         where u.UsersID == userID                         select u).FirstOrDefault();              if (user != null)             {                 this._user = user;             }             else             {                 this._user = new Xxx.Entities.User();                  base.Users.InsertOnSubmit(this._user);             }         }           public User(Xxx.User.SiteAccessRights accessRights, String alias)         {             var user = (from u in base.Users                         where u.UsersAccessRights == (Int32)accessRights && u.UsersAlias == alias                         select u).FirstOrDefault();              if (user != null)             {                 this._user = user;             }             else             {                 this._user = new Xxx.Entities.User                 {                     UsersAccessRights = (Int32)accessRights,                     UsersAlias = alias                 };                  base.Users.InsertOnSubmit(this._user);             }         }           public void DeleteOnSubmit()         {             base.Users.DeleteOnSubmit(this._user);         }     } } 

Update:

Notice that I have two constructor-methods in my User class. I’d like to transfer those to the User entity-class and extend the User entity-class on it’s data-context class, so that the data-context is available to the entity-class on ‘new-up’.

Hope this makes sense.

Answer 1

It doesn’t seem to make sense to make an entity a type of DataContext. It doesn’t need to be a DataContext in order to be considered a business object, nor do you necessarily need to create a type that contains the original entity. It might be better to just extend the entity class and contain a reference to a DataContext using composition:

namespace Xxx.Entities {   public partial class User : IDisposable    { DataContext ctx;       public static GetUserByID(int userID)       {  var ctx  = new DataContext();          var user = ctx.Users.FirstOrDefault(u=>u.UsersID == userID);           if (user == null)           {              user = new User();              ctx.Users.InsertOnSubmit(user);           }           user.ctx = ctx;          return user;                 }             public void Dispose() { if (ctx != null) ctx.Dispose(); }    } } 

If you just want the property names to be different than the database column names, do that in the mapping file.