Entity Framework query to custom object Class with List - entity-framework

Question

I am using entity frame work for Web API 2.0 I am trying to query Author Book to a custom Object.
Object is :
public class AuthorBooks
{
public Author Author;
public List<BookDetail> BookDetails;
public AuthorBooks() {
Author = new Author();
BookDetails = new List<BookDetail>();
}
}
public class BookDetail
{
public BookDetail()
{
Book = new Book();
Category = new Category();
SubCategory = new SubCategory();
}
public Book Book { get; set; }
public Category Category { get; set; }
public SubCategory SubCategory { get; set; }
}
Here Book, Author, Category and SubCategory are entities
Relation presently working properly is:
Author
----List
public class AuthorBooks
{
public Author Author;
public List<Book> Book;
public AuthorBooks() {
Author = new Author();
Book = new List<Book>();
}
}
using query I get proper result :
AuthorBooks authorBooks = (from a in _context.Authors.Where(author => author.Id == id)
join b in _context.Books on a.Id equals b.AuthorName into b1
select new AuthorBooks { Author = a, Book = b1.ToList() }).Single<AuthorBooks>();
But Now for Above Mentioned Relation :
Author
---List
where Book Detail of other Entities related by Id's of Entities Category and SubCategory.
So How Can It be Done with BookDetails Id???
AuthorBooks authorBooks = (from a in _context.Authors.Where(author => author.Id == id)
join b in _context.Books on a.Id equals b.AuthorName into b1
from b2 in b1
join c in _context.Categories on b2.CategoryId equals c.Id
join s in _context.SubCategories on b2.SubCategoryId equals s.Id
select new AuthorBooks { Author = a, BookDetails = #####List<BookDetail>####### }).Single<AuthorBooks>();

Answer 1

You need to join the necessary data needed for BookDetail in a subquery and then group join the authors query to it to get the desired author - list of detail correlation:
AuthorBooks authorBooks = (
from a in _context.Authors.Where(author => author.Id == id)
join bd in (from b in _context.Books
join c in _context.Categories on b.CategoryId equals c.Id
join s in _context.SubCategories on b.SubCategoryId equals s.Id
select new BookDetail { Book = b, Category = c, SubCategory = s }
) on a.Id equals bd.Book.AuthorName into bookDetails
select new AuthorBooks { Author = a, BookDetails = bookDetails.ToList() }
).Single();