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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.
## 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 < 2.3. But now it has become easier and easier to associate
models and worrying less about your structure.
|
