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+---
+layout: post
+title: Relationships in Rails 2.3
+tags: [ development, rails ]
+type: post
+published: true
+---
+
+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.
+
+## Case study: a school
+
+The example I am going to show my attendees resembles a typical school
+situation. In a nutsheel:
+
+* Students have Subjects.
+* Subjects have Students.
+* Students have Grades to Subjects.
+
+![Rails relationships — student](/wp-content/uploads/2009/07/rails-relationships-student.png)
+
+## The Models
+
+### Student
+
+{% highlight ruby %}
+class Student < ActiveRecord::Base
+   has_many :grades
+   has_many :subjects, :through => :grades, :uniq => true
+   accepts_nested_attributes_for :grades, :allow_destroy => true
+end
+{% endhighlight %}
+
+### Subject
+
+{% highlight ruby %}
+class Subject < ActiveRecord::Base
+  validates_uniqueness_of :shortname
+  has_many :grades
+  has_many :students, :through => :grades, :uniq => true
+end
+{% endhighlight %}
+
+### Grade
+
+{% highlight ruby %}
+class Grade < ActiveRecord::Base
+  belongs_to :subject
+  belongs_to :student
+  validates_presence_of :value
+end
+{% endhighlight %}
+
+## And the magic trick!
+
+Through `accepts_nested_attributes_for`, the student's `form_for` can now
+accept nested fields through `fields_for` 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 [Complex
+Forms](http://railscasts.com/episodes?search=complex+forms) series 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.