Group加入幷包括

Question

GroupJoin後，我想包括Book.Authors，因爲字段Book.Authors將爲空。 但我不能。我該怎麼做才能解決這個問題？

Queryable<NewRead> recent = Repository.NewReads.Where(x => x.UserId == usersId); 

var newFavs = IsAuthorized ? Repository.NewFavs.Where(x => x.UserId == UserId) : Repository.NewFavs.Where(x => false); 

var recentFavorite = recent.GroupJoin(newFavs, 
          x => x.BookId, 
          y => y.BookId, 
          (x, y) => new {Recent = x, Favorite = y, x.Book}); 

我想：

var recent = Repository.NewReads.Include("Book.Authors") 
        .Where(x => x.UserId == usersId); 

和

var newFavs = IsAuthorized ? Repository.NewFavs.Include("Book.Authors").Where(x => x.UserId == UserId) : Repository.NewFavs.Where(x => false); 

而這一切都在一起。 它在GroupJoin之前工作，但在Authors字段丟失之後。 如果我添加：

var recentFavorite = recent.GroupJoin(newFavs, 
          x => x.BookId, 
          y => y.BookId, 
          (x, y) => new {Recent = x, Favorite = y, x.Book, x.Book.Authors}); 

所有工作正常，但它不是解決方案。

Answer 1

可以

var recent = Repository.NewReads.Include(x => x.Book.Authors) 
         .Where(x => x.UserId == usersId); 

Answer 2

var recent = Repository.NewReads.Include("Book").Where(n => n.UserId == usersId).FirstOrDefault().Book.Select(b=>b.Authors);