# Books belongs\_to authors. How to find only author with books **URL:** \ **Category:** Rails\ **Created:** [June 1, 2008, 10:15pm UTC](https://www.ruby-forum.com/t/books-belongs-to-authors-how-to-find-only-author-with-books/139212 "2008-06-01T22:15:14Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![ferblape](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/73ab20/32.png) [@ferblape](https://www.ruby-forum.com/u/ferblape)\ **Post date:** [June 1, 2008, 10:15pm UTC](https://www.ruby-forum.com/t/books-belongs-to-authors-how-to-find-only-author-with-books/139212/1 "2008-06-01T22:15:14Z")
Hello I have a table called Books And a table called Authors Books belong\_to authors How can I find only authors that have books? Thanks ---
**Author:** ![ferblape](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/73ab20/32.png) [@ferblape](https://www.ruby-forum.com/u/ferblape)\ **Post date:** [June 1, 2008, 11:08pm UTC](https://www.ruby-forum.com/t/books-belongs-to-authors-how-to-find-only-author-with-books/139212/2 "2008-06-01T23:08:29Z")
Fernando B. wrote: > Hello > > I have a table called Books > And a table called Authors > > Books belong\_to authors > > How can I find only authors that have books? > > Thanks I think an author can write many books so that you can put has\_many :books in Author ActiveRecord so that you can find books easily @author = Author.find(:first) @books = @author.books Reinhart [http://teapoci.blogspot.com](http://teapoci.blogspot.com) ---
**Author:** ![ferblape](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/73ab20/32.png) [@ferblape](https://www.ruby-forum.com/u/ferblape)\ **Post date:** [June 1, 2008, 11:30pm UTC](https://www.ruby-forum.com/t/books-belongs-to-authors-how-to-find-only-author-with-books/139212/3 "2008-06-01T23:30:45Z")
I thought I’d point out too that one book can have multiple authors, so you might need something like Book id name Writings book\_id author\_id Author id name and use something like Books has\_many :authors, :through =\> :writings Writings belongs\_to :book, belongs\_to :author Author has\_many :books, :through =\> :writings To get that many to many relationship working. As for your question, and using the above, now all you need to do is construct a find query to get authors if COUNT(\*) FROM writings WHERE author\_id = [id here] and check its size is \> 0 That would be my solution anyway. A more exp. rails dev might have a faster option. Regards Kieran On Mon, Jun 2, 2008 at 9:08 AM, Rails T. \< ---
**Author:** ![ferblape](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/73ab20/32.png) [@ferblape](https://www.ruby-forum.com/u/ferblape)\ **Post date:** [June 2, 2008, 4:35am UTC](https://www.ruby-forum.com/t/books-belongs-to-authors-how-to-find-only-author-with-books/139212/4 "2008-06-02T04:35:41Z")
This is not optimal code, but you can make a method in Author: def self.find\_all\_with\_books authors = [] for author in self.find(:all) authors \<\< author if author.books.count \> 0 end authors end If you’re using Rails 2.1 you can check out named\_scope. Not familiar with it yet, but it goes something like this class Author \< … has\_many :books named\_scope :published, :include =\> :books, :conditions =\> [“books.count \> 0”] I’m pretty sure the code won’t work. Watch this to be more familiar with it though [#108 named\_scope - RailsCasts](http://railscasts.com/episodes/108) On Mon, Jun 2, 2008 at 4:15 AM, Fernando B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > ## Thanks > > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). > > > – Ramon T. ---
**Author:** ![ferblape](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/73ab20/32.png) [@ferblape](https://www.ruby-forum.com/u/ferblape)\ **Post date:** [June 2, 2008, 2:51pm UTC](https://www.ruby-forum.com/t/books-belongs-to-authors-how-to-find-only-author-with-books/139212/5 "2008-06-02T14:51:02Z")
On Mon, Jun 2, 2008 at 8:27 AM, sullivan.t [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I like that, though what about finding the db records with sql and a > standard table join? > > I suppose it’d be the same in terms of cpu cycles, etc. No it wouldn’t, doing it in SQL would result in one query and less cycles. Something like: Author.find(:all, :joins =\> :books) Should do the trick, this should do a query with an inner equijoin on Authors and Books, so Authors without books would not be returned. Note that I haven’t actually tested this code. – Rick DeNatale My blog on Ruby [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) ---
**Author:** ![ferblape](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/73ab20/32.png) [@ferblape](https://www.ruby-forum.com/u/ferblape)\ **Post date:** [June 2, 2008, 2:28pm UTC](https://www.ruby-forum.com/t/books-belongs-to-authors-how-to-find-only-author-with-books/139212/6 "2008-06-02T14:28:23Z")
I like that, though what about finding the db records with sql and a standard table join? I suppose it’d be the same in terms of cpu cycles, etc. On Jun 1, 10:34 pm, “Ramon Miguel M. Tayag” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![ferblape](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/73ab20/32.png) [@ferblape](https://www.ruby-forum.com/u/ferblape)\ **Post date:** [June 2, 2008, 2:59pm UTC](https://www.ruby-forum.com/t/books-belongs-to-authors-how-to-find-only-author-with-books/139212/7 "2008-06-02T14:59:52Z")
On 2 Jun 2008, at 13:50, Rick DeNatale wrote: > Something like: > > Author.find(:all, :joins =\> :books) > > Should do the trick, this should do a query with an inner equijoin > on Authors and Books, so Authors without books would not be returned. > > Note that I haven’t actually tested this code. There’s always the cheat’s version: have a counter\_cache on books. Fred ---
**Author:** ![ferblape](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/73ab20/32.png) [@ferblape](https://www.ruby-forum.com/u/ferblape)\ **Post date:** [June 2, 2008, 3:34pm UTC](https://www.ruby-forum.com/t/books-belongs-to-authors-how-to-find-only-author-with-books/139212/8 "2008-06-02T15:34:16Z")
Hey everyone! Well what do you know? I had to do this today, right after I emailed. If you’re going to use named\_scope, you have to setup a counter cache. > **[\#23 Counter Cache Column - RailsCasts](http://railscasts.com/episodes/23-counter-cache-column)** > > Short Ruby on Rails screencasts containing tips, tricks and tutorials. Great for both novice and experienced web developers. then, in Author: named\_scope :published, :conditions =\> [“books\_count \> 0”] if not named\_scope, try: Author.find(:all, :conditions =\> [“books\_count \> 0”]) Either way, counter\_cache would be a good thing to setup since doing these kinds of finds will be a lot less CPU intensive. – Ramon T.