Include only the latest/newest associated record with active record?

Question

is it possible to load only the latest associated record of an associated table? an example: ``` class author attr_accessible :first_name, :last_name, :birthday has_many :books end class book attr_accessible :pages, :date of publication, :title belongs_to :author end ``` Is there a way to generate a scope to load only the newest released book the author wrote? Or the book with the most pages? I know, that I could include or join all books. But I don't know if its possible to load only a specific book for each author. So that I could do a query like this: ``` Author.authors_and_their_newest_book ``` So that I could get these results ``` first_name_author_1, last_name_author_1, birthday_author_1, pages_book_3, date_of_publication_book_3, title_book_3 first_name_author_2, last_name_author_2, birthday_author_2, pages_book_5, date_of_publication_book_5, title_book_5 first_name_author_3, last_name_author_3, birthday_author_3, pages_book_9, date_of_publication_book_9, title_book_9 ``` ... up…

Accepted Answer

This is a working scope with lambda to pass parameters to the scope to select the genre id.

```
scope :latest_with_genre, lambda do |searched_genre_id|
  joins(:books)
    .where('books.date_of_publication = (SELECT MAX(books.date_of_publication) FROM books WHERE books.author_id = authors.id)')
    .where("books.genre_id = #{searched_genre_id}").group('author.id')
end
```

This answer Rails query through association limited to most recent record? from Pan Thomakos helped me for the scope. This answer Pass arguments in scope from keymone helped me for passing argument

Include only the latest/newest associated record with active record?

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