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----
-layout: post
-title: Relationships in Rails 2.3
-tags:
-- Development
-- rails
-status: publish
-type: post
-published: true
-meta:
-  _edit_last: '1'
----
-Ruby on Rails is becoming quite a piece of software. I've been learning how to work with its latest version to date, 2.3, for a series of workshops on web development. It has surprised me how easy it is now to accomplish a simple task such as multi-model form processing. Let me show what I've been doing lately.
-
-<!--more-->
-<h3>Case study: a school</h3>
-The example I am going to show my attendees resembles a typical school situation. In a nutsheel:
-<ul>
-	<li>Students have Subjects.</li>
-	<li>Subjects have Students.</li>
-	<li>Students have Grades to Subjects.</li>
-</ul>
-[caption id="attachment_78" align="alignnone" width="442" caption="Rails relationships — student"]<a href="/wp-content/uploads/2009/07/rails-relationships-student.png"><img class="size-full wp-image-78" title="Rails relationships — student" src="/wp-content/uploads/2009/07/rails-relationships-student.png" alt="Rails relationships — student" width="442" height="98" /></a>[/caption]
-<h3>The Models</h3>
-<h4>Student</h4>
-<pre class='brush:rails'>class Student < ActiveRecord::Base
-   has_many :grades
-   has_many :subjects, :through => :grades, :uniq => true
-   accepts_nested_attributes_for :grades, :allow_destroy => true
-end</pre>
-<h4>Subject</h4>
-<pre class='brush:rails'>class Subject < ActiveRecord::Base
-  validates_uniqueness_of :shortname
-  has_many :grades
-  has_many :students, :through => :grades, :uniq => true
-end
-</pre>
-<h4>Grade</h4>
-<pre class='brush:rails'>class Grade < ActiveRecord::Base
-  belongs_to :subject
-  belongs_to :student
-  validates_presence_of :value
-end
-</pre>
-<h3>And the magic trick!</h3>
-Through <em>accepts_nested_attributes_for</em>, the student's <em>form_for</em> can now accept nested fields through <em>fields_for</em> for setting Grades' data.
-
-Everytime a student is created, subjects are not directly associated to him. You need to create a form in which you allow to assign a student the subjects you want.
-
-[image missing]
-
-This tells you that a student can have an array of subject id's. You even get to see what subjects are already assigned and dissociate them just like that! When the associations are done, a new Grade record is created to associate the first two modules. Unfortunately, when the associations are dismantled, the Grade association is gone too.
-
-If you know Railscasts, the <a href="http://railscasts.com/episodes?search=complex+forms">Complex Forms series</a> explain this task for Rails &lt; 2.3. But now it has become easier and easier to associate models and worrying less about your structure.