Implementing the Repository and Unit of Work Patterns in ASP.NET

Question

Has anyone read this article on www.asp.net titled "Implementing the Repository and Unit of Work Patterns in an ASP.NET MVC Application (9 of 10)"

http://www.asp.net/mvc/tutorials/getting-started-with-ef-5-using-mvc-4/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application

In the article it says: "This generic repository will handle typical CRUD requirements. When a particular entity type has special requirements, such as more complex filtering or ordering, you can create a derived class that has additional methods for that type."

Can anyone explain in detail how can I create a derived class and use these additional methods? Do I put additional methods in the generic repository as virtual methods?

Please help, I cannot figure out how to do this. Thanks a lot.

Answer 1

Here is an example:

public class GenericRepository<TEntity> where TEntity : class
{
    public virtual TEntity GetByID(object id)
    {
        // ...
    }

    public virtual void Insert(TEntity entity)
    {
        // ...
    }

    public virtual void Delete(TEntity entityToDelete)
    {
        // ...
    }
}

These methods would apply to all your entities. However let's say you want to get a User by an email (a property that only the user has) you can extend the GenericRepository with your additional method:

public class UserRepository : GenericRepository<User>
{
    // Now the User repository has all the methods of the Generic Repository
    // with addition to something a bit more specific
    public User GetByEmail(string email)
    {
        // ..
    }
}

Edit - In the article they're using a GenericRepository in the Unit of Work, but when your repository is more specific you use it instead. For example:

public class UnitOfWork : IDisposable
{
    private GenericRepository<Department> departmentRepository;
    private GenericRepository<Course> courseRepository;

    // here is the one we created, which is essentially a GenericRepository as well
    private UserRepository userRepository;

    public UserRepository UserRepository
    {
        get
        {

            if (this.userRepository== null)
            {
                this.userRepository= new UserRepository(context);
            }
            return this.userRepository;
        }
    }

   // ...
}