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

Question

Can I load only the last related record of a linked table?

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 create a download area for only the latest released book that the author wrote? Or a book with most pages?

I know that I can include or join all books. But I do not know if it is possible to download only a specific book for each author.

So that I can make such a request:

Author.authors_and_their_newest_book

To 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

...

update: I understand that my real problem is not resolved by answering this question.

There is a third model that I should consider.

class author
  attr_accessible :first_name, :last_name, :birthday
  has_many :books
end

class book
  attr_accessible :pages, :date of publication, :title, _genre_id
  belongs_to :author
  belongs_to :genre
end

class genre
  attr_accessible :name
  has_many :books
end

My real problem is that I want to filter using area

scope :with_latest_book_is_a_thriller
scope :with_latest_book_is_a_science_fiction
scope :with_latest_book_is_a_genre_xyz
...

, , genre_id. , ", - xyz", " xyz".

, , :

author_1: Bruce Wayne  
books:   
title: "how to fight a villain",date_of_publication: March 2010,genre: self-help,  
title: "my life as batman",date_of_publication: April 2012,genre: biography,  
title: "developing high tech equipment", date_of_publication: January 2013, genre: science  

author_2: Clark Kent  
books:  
title: "how I crossed the universe", date_of_publication: January 2009, genre: biography,  
title: "controlling a freezing breath", date_of_publication: February 2012, genre: self-help,  
title: "Clark Kent as Batman", date_of_publication: December 2013, genre: fiction  

author_3: Peter Parker  
books:  
title: "Spider-Man life", date_of_publication: January 2010, genre: biography,  
title: "how to handle a life with a clone", date_of_publication: February 2011, genre: self-help,  
title: "Spider-Man is becoming a baker", date_of_publication: November 2013, genre: fiction  

:

scope :with_latest_book_is_a_self_help => empty result  
scope :with_latest_book_is_a_biography => empty result  
scope :with_latest_book_is_a_science => Bruce Wayne, "developing high tech equipment"  
scope :with_latest_book_is_a_fiction => Clark Kent, "Clark Kent as Batman"; Peter Parker, "Spider-Man is becoming a baker" 

:

scope :with_latest_book_is_a_self_help => Bruce Wayne, "how to fight a villain"; Clark Kent, "controlling a freezing breath"; Peter Parker, "how to handle a life with a clone"

? ?

Answer 1

lambda , .

scope :latest_with_genre, lambda{|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') }

Rails- , ? .
keymone

Answer 2

,

class author
  attr_accessible :first_name, :last_name, :birthday
  has_many :books

  scope :latest, joins(:books).where('books.author_id = authors.id').order('date_of_publication DESC').group('authors.id')
end

, , Book.

class book
  attr_accessible :pages, :date of publication, :title, _genre_id
  belongs_to :author
  belongs_to :genre

  scope :latest_with_genre, joins(:author,:genre).where("author_id =?","genre_id =?,author.id,genre.id).order('date_of_publication DESC').group('author.id','genre.id')

end

, .