Entity Framework subquery

Question

Guys I am new to Entity Framework and I\'m having a bt of a problem that I have been trying to solve for quite a while. Basically I have 4 entities: users, groups, books an

Answer 1

I haven't tested it but hopefully it will work.

entities.Books.Where(
b => entities.ReadingList.
Where(rl => rl.GroupId == groupId).
Select(rl => rl.BookId).
Contains(b.BookId)
)

Answer 2

Personally I think there is a better solution(untested of course):

First select from ReadList by GroupdID, then join in books on BookID.

IQueryable<Book> q = 
       from rl in entities.ReadingList
       join b in entities.Books on rl.BookID equals b.BookID
       where rl.GroupdID ==groupID
       select b;

var books = q.ToList()

Please let me know if you have any issues.