Entity Framework generic repository. Meant to be used as a wrapper to access a particular type/table from DbContext

GenericRepository.cs

public class GenericRepository<T> : IRepository<T> where T : class
  {
      protected DbSet<T> DBSet {get;set;}
      protected DbContext Context { get; set; }

      public GenericRepository(DbContext context)
      {
          if (context == null)
          {
              throw new ArgumentException("An instance of DbContext is " +
                  "required to use this repository.", "context");
          }

          this.Context = context;
          this.DBSet = this.Context.Set<T>();
      }

      public virtual IQueryable<T> GetAll()
      {
          return this.DBSet;
      }

      public virtual T GetById(int id)
      {
          return this.DBSet.Find(id);
      }

      public virtual void Add(T entity)
      {
          DbEntityEntry entry = this.Context.Entry(entity);
          if (entry.State != EntityState.Detached)
          {
              entry.State = EntityState.Added;
          }
          else
          {
              this.DBSet.Add(entity);
          }
      }

      public virtual void Update(T entity)
      {
          DbEntityEntry entry = this.Context.Entry(entity);

          if (entry.State == EntityState.Detached)
          {
              this.DBSet.Attach(entity);
          }

          entry.State = EntityState.Modified;
      }

      public virtual void Detach(T entity)
      {
          DbEntityEntry entry = this.Context.Entry(entity);

          entry.State = EntityState.Detached;
      }

      public virtual void Delete(T entity)
      {
          DbEntityEntry entry = this.Context.Entry(entity);

          if (entry.State != EntityState.Deleted)
          {
              entry.State = EntityState.Deleted;
          }
          else
          {
              this.DBSet.Attach(entity);
              this.DBSet.Remove(entity);
          }
      }

      public virtual void Delete(int id)
      {
          var entity = this.GetById(id);

          if (entity != null)
          {
              this.Delete(entity);
          }
      }
  }

IRepository.cs

public interface IRepository<T> where T : class
{
    IQueryable<T> GetAll();
    T GetById(int id);
    void Add(T entity);
    void Update(T entity);
    void Delete(T entity);
    void Delete(int id);
    void Detach(T entity);
}