Question

I have a User, Book and UserBooks releation table. UserBooks table like this

|UserID | BookID  | Status    |    1        34      Read    1        35      Unread     2        34      Read    2        70      Read    2        32      Unread      ................... 

My domain classes are User,Book and UserBook. in NHibernate how can I get top 10 most read books and their read count by users?

Top 10 Read Books

| BookID | ReadCount |    34         2    70         1    ............... 

Answer 1

Assuming you are using composite-element to map your UserBook class:

var top10Books = session     .CreateQuery(@'select b.Book                     from User u                     join fetch u.Books b                     where b.Status = :status')     .SetParameter('status', 'Read')     .SetMaxResults(10)     .SetResultTransformer(CriteriaSpecification.DistinctRootEntity)     .List<Book>(); 

And here’s the link to the complete source code.

EDIT:

I see that you require the number of times a book has been read. Here’s the query:

var top = session     .CreateQuery(@'select b.Book, count(b.Book.Id)                     from User u join fetch u.Books b                     where b.Status = :status                     group by b.Book')     .SetParameter('status', 'Read')     .SetMaxResults(10)     .List<object[]>();      foreach (var item in top)     {         var book = (Book)item[0];         var readCount = (long)item[1];         Console.WriteLine('book id: {0}, read count: {1}', book.Id, readCount);     }