如何检索存储库模式中的相关数据？

Question

我用过这篇文章  [http://www.codeproject.com/Articles/615499/Models-POCO-Entity-Framework-and-Data-Patterns][1] 实现我的存储库模式：

例如，我有这个模型和repo实现：

   public class Teacher
    {
        public Teacher()
        {
            this.Reshte = new Reshte();
            this.City = new City();
            this.Books = new HashSet<TeacherBook>();
        }
        public int ID { get; set; }
        public string Name { get; set; }
        public string Family { get; set; }
        public string Tell { get; set; }
        int CityID { get; set; }
        public City City { get; set; }
        public string Attend { get; set; }
        public Reshte Reshte { get; set; }
        int ReshteID { get; set; }
        public bool Recruitment { get; set; }//True rasmi False gharardady
        public DateTime Date { get; set; }
        public virtual ICollection<TeacherBook> Books { get; set;}
    }

  public class TeacherBook
    {
        public int ID { get; set; }
        public int TeacherID { get; set; }
        public  int BookID { get; set; }
        public virtual Teacher Teacher { get; set; }
        public virtual Book Book { get; set; }

        public string Day { get; set; }

    }

   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);


    }



  public class Repository<T>:IRepository<T> where T:class
    {
        protected DbContext DbContext{ get; set; }
        protected DbSet<T> DbSet { get; set; }
        public Repository(DbContext dbContext)
        {
            if (dbContext!=null)
            {
                DbContext = dbContext;
                DbSet = DbContext.Set<T>();
            }
        }
        public IQueryable<T> GetAll()
        {
            return DbSet.ToList().AsQueryable();
        }

        public T GetByID(int id)
        {
            return DbSet.Find(id);
        }

        public virtual void ADD(T entity)
        {
            var res = DbContext.Entry(entity);
            if (res.State != System.Data.EntityState.Detached)
            {
                res.State = System.Data.EntityState.Added;
            }
            else
                DbSet.Add(entity);
        }

        public void Update(T entity)
        {
            DbEntityEntry res = DbContext.Entry(entity);
            if (res.State != System.Data.EntityState.Detached)
            { 
                DbSet.Attach(entity);

            }
             res.State = System.Data.EntityState.Modified;

        }

        public void Delete(T entity)
        {
            DbEntityEntry res = DbContext.Entry(entity);
            if (res.State!=System.Data.EntityState.Deleted)
            {
                res.State = System.Data.EntityState.Deleted;
            }
            else
            {
                DbSet.Attach(entity);
                DbSet.Remove(entity);

            }
        }

        public void Delete(int ID)
        {
            var res = GetByID(ID);
            if (res == null)
                return;
            else
                Delete(res);
        }
    }

public class TeacherBookRepository:Repository<TeacherBook>,ITeacherBookRepository
    {
        public TeacherBookRepository(System.Data.Entity.DbContext DbContext):base(DbContext)
        {

        }
            public IEnumerable GetTeacherBookList()
            {
                return GetAll().Select(x => new {ID=x.ID,BookName=x.Book.Name,Day=Day(x.Day), }).ToList();
            }

            private object Day(string p)
            {
     //...
            }
        }

当我想要检索数据时，导航属性的相关数据为空。例如 在GetTeacherBookList方法的结果中，bookName为null。 如何解决这个问题？