# Getting started with Ruby on Rails and Relationships **URL:** \ **Category:** Rails\ **Created:** [May 30, 2007, 3:45pm UTC](https://www.ruby-forum.com/t/getting-started-with-ruby-on-rails-and-relationships/105506 "2007-05-30T15:45:42Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![revanche](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ac91a4/32.png) [@revanche](https://www.ruby-forum.com/u/revanche)\ **Post date:** [May 30, 2007, 3:45pm UTC](https://www.ruby-forum.com/t/getting-started-with-ruby-on-rails-and-relationships/105506/1 "2007-05-30T15:45:42Z")
Hello! I’m relatively new to Ruby on Rails, but decided to start experimenting with it after looking at how it can simply some rather repetitive tasks that I find myself writing with PHP. For the most part, I’ve been learning through books and writing code, as expected, and tend to plug away at something until I can get it right. Working with relationships, however, has proven a bit difficult so I thought I would try to solicit some help from anyone willing… As part of this experiment, I’m building a sample bookstore that has two database tables (author, book). Author is setup as has\_many :book, and book as has\_one :author Authors simply has id, firstname, lastname fields while book stores id, title, description, author\_id Inside the book controller, it calls a simple find to display all books by a particular author @results = Book.find(:all, :conditions =\> { :author\_id =\> entry.id}) Entry.id is a numeric value provided by a form on a previous page. The view page itself is: \<% @results.each do |result| %\> \<%= h(book.title)%\> \<%= h(book.description)%\> \<% end %\> All of this works fine. The question is: Given the setup, how do I display the appropriate first and last name of the author for each book? I’ve tried a variety of different approaches to no avail, and I’m guessing its just a minor error in my methodology. ---
**Author:** ![revanche](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ac91a4/32.png) [@revanche](https://www.ruby-forum.com/u/revanche)\ **Post date:** [May 30, 2007, 4:46pm UTC](https://www.ruby-forum.com/t/getting-started-with-ruby-on-rails-and-relationships/105506/2 "2007-05-30T16:46:17Z")
Hi, As a side-note, instead of doing @results = Book.find(:all, :conditions =\> { :author\_id =\> entry.id}) You can do this: @results = Author.find(entry.id).books Or if entry is already an author instance @results = entry.books This also infers that your relations ships are: has\_many :books and belongs\_to :author On to your actual question, you would want to do: \<% @results.each do |result| %\> \<%= h(book.title) %\> \<%= h(book.description) %\> \<%= h(book.author.firstname) %\> \<%= h(book.author.lastname) %\> \<% end %\> If this gives you problems, check that your relationships are like I said above: has\_many :books on the author model belongs\_to :author on the book model Hope this helps. Cheers, James ---
**Author:** ![revanche](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ac91a4/32.png) [@revanche](https://www.ruby-forum.com/u/revanche)\ **Post date:** [May 30, 2007, 4:51pm UTC](https://www.ruby-forum.com/t/getting-started-with-ruby-on-rails-and-relationships/105506/3 "2007-05-30T16:51:49Z")
If you have a has\_many/belongs\_to relationship between authors and books, finding one should give you access to the other. For example, if author has\_many books, you should be able to do this: a = Author.find(entry.id) # returns author object with id == entry.id @results = a.books # collections of books by the author Then you should be able to access a.firs\_name and a.last\_name (or whatever). The Rails console is your friend. In a terminal, cd to the root of your app, then enter “script/console” (or “ruby script/console”). You can enter the lines above (with real numbers, of course) and see the author object, and then see if an array of books is returned (assuming you have relationships). Neil H. wrote: > Hello! I’m relatively new to Ruby on Rails, but decided to start > experimenting with it after looking at how it can simply some rather > repetitive tasks that I find myself writing with PHP. For the most part, > I’ve been learning through books and writing code, as expected, and tend > to plug away at something until I can get it right. Working with > relationships, however, has proven a bit difficult so I thought I would > try to solicit some help from anyone willing… > > As part of this experiment, I’m building a sample bookstore that has two > database tables (author, book). Author is setup as has\_many :book, and > book as has\_one :author > > Authors simply has id, firstname, lastname fields while book stores id, > title, description, author\_id > > Inside the book controller, it calls a simple find to display all books > by a particular author > > @results = Book.find(:all, :conditions =\> { :author\_id =\> entry.id}) > > Entry.id is a numeric value provided by a form on a previous page. > > The view page itself is: > > \<% @results.each do |result| %\> > \<%= h(book.title)%\> > \<%= h(book.description)%\> > \<% end %\> > > All of this works fine. > > The question is: Given the setup, how do I display the appropriate first > and last name of the author for each book? I’ve tried a variety of > different approaches to no avail, and I’m guessing its just a minor > error in my methodology. ---
**Author:** ![revanche](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ac91a4/32.png) [@revanche](https://www.ruby-forum.com/u/revanche)\ **Post date:** [May 30, 2007, 5:04pm UTC](https://www.ruby-forum.com/t/getting-started-with-ruby-on-rails-and-relationships/105506/4 "2007-05-30T17:04:35Z")
Thank you! Just one follow-up… On your recommendation for using @results = Author.find(entry.id).books instead of my longer Find query, how would you appropriately adjust it if we expanded to check multiple fields. Say we created a new field, status. Would @results = Author.find(entry.id, status).books be appropriate? James Brooks wrote: > Hi, > > As a side-note, instead of doing > @results = Book.find(:all, :conditions =\> { :author\_id =\> entry.id}) > > You can do this: > @results = Author.find(entry.id).books > > Or if entry is already an author instance > @results = entry.books > > This also infers that your relations ships are: > has\_many :books and belongs\_to :author > > On to your actual question, you would want to do: > > \<% @results.each do |result| %\> > \<%= h(book.title) %\> > \<%= h(book.description) %\> > \<%= h(book.author.firstname) %\> > \<%= h(book.author.lastname) %\> > \<% end %\> > > If this gives you problems, check that your relationships are like I > said > above: > has\_many :books on the author model > belongs\_to :author on the book model > > Hope this helps. > > Cheers, > James ---
**Author:** ![revanche](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ac91a4/32.png) [@revanche](https://www.ruby-forum.com/u/revanche)\ **Post date:** [May 31, 2007, 12:11am UTC](https://www.ruby-forum.com/t/getting-started-with-ruby-on-rails-and-relationships/105506/5 "2007-05-31T00:11:28Z")
Rails has some magic finders. To find based on one attribute, like lastName, use Author.find\_by\_lastName(‘wibble’) To find on two attributes, like lastName and status, use Author.find\_by\_lastName\_and\_status(‘wibble’, ‘dead’) These finders only return one record (the first one they find in the db, which may not be the one you expect). To find all records that match the criteria, use instead Author. find\_all\_by… Finding by a record’s id is a special case, which is the one I originally presented: Author.find(id), so your construction will not work. If you need to search on more fields (like lastName, firstName, and status) you’ll have to use find(:all) with modifiers. That’s a bit much to go into here, but is well covered in the Agile Web D. book. To give you an idea, a query could be written as Author.find(:all, :conditions =\> “lastName = ‘wibble’ and status = ‘dead’”) BTW, if you are pulling the values for comparison (i.e., ‘wibble’ and ‘dead’ in my example) from form fields, make sure you understand SQL Injection before you do anything like the above query. [http://www.google.com/search?q=rails+sql+injection](http://www.google.com/search?q=rails+sql+injection) Neil H. wrote: > Thank you! > > Just one follow-up… > > On your recommendation for using > @results = Author.find(entry.id).books instead of my longer Find query, > how would you appropriately adjust it if we expanded to check multiple > fields. Say we created a new field, status. > > Would @results = Author.find(entry.id, status).books be appropriate?