public class Book
{
public int Id { get; set; }
public string Title { get; set; }
public Author Author { get; set; }
}

public class Author
{
public int Id { get; set; }
public string Name { get; set; }
public DateTime? Birthdate { get; set; }
public virtual ICollection<Book> Books { get; set; }
}

        public Book GetByIdWithAuthor(int id)
        {
            var query = _dbcontext.Set<Book>().Include(b => b.Author) as IQueryable<Book>;

            return query.FirstOrDefault(b => b.Id == id);
        }

public Book GetByIdWithAuthor(int id)
        {                                                
            return _dbcontext.Set<Book>().SqlQuery("dbo.GetBookByIdWithAuthor @p0", id).FirstOrDefault();
        }