Help with rails nested forms - ruby-on-rails

Question

I have these three models.
Student.
Evaluation.
Grade (student_id, evaluatioin_id, value)
I want to make a form so that a User can set the grade for each student of a evaluation...
I want to keep this is as clean as possible (and restful)...
Im open to any suggestions on how to get this done.
Please Help.

Answer 1

See these
http://railscasts.com/episodes/196-nested-model-form-part-1
http://railscasts.com/episodes/197-nested-model-form-part-2

Answer 2

I suppose you have the following associations:
Evaluation:
class Evaluation < ActiveRecord:Base
has_many :grades
accepts_nested_attributes_for :grades
end
Student:
class Student < ActiveRecord::Base
has_many :grades
end
Grade:
class Grade < ActiveRecord::Base
belongs_to :student
blongs_to :evaluation
end
Regarding your comment I think you want to use the nested_form_for gem made by Ryan Bates. It helps you add/delete dynamically nested attributes in your form, very efficiently. You can use it like this:
<% nested_form_for #evaluation do |f| %>
<% f.fields_for :grades do |gf| %>
<%= gf.label 'Username of the student' %>
<%= gf.collection_select(:student, :student_id, Student.All, :id, :username) %> <br/>
<%= gf.label :value %>
<%= gf.text_field :value %> <br/>
<%= gf.link_to_remove 'delete' %> <br/>
<% end %>
<%= f.link_to_add 'Add grade', :grades %> <br/>
<%= f.submit %>
<% end %>
Tell me if it works/fits your needs. I have been using this gem a lot these previous days.

Answer 3

What I ended up doing was..
In Grade Model
scope :for_student,lambda{|student, evaluation| where("student_id"=>student.id).where("evaluation_id"=>evaluation.id)}
In EvaluationsController
def assign_grades])
#evaluation = Evaluation.find(params[:id])
#students = Student.all
#students.each do |s|
grade = Grade.for_student(s,#evaluation)
if !grade.exists?
#evaluation.grades.build(:value=> 0,:student_id=>s.id)
end
end
end
def save_grades
#evaluation = Evaluation.find(params[:id])
#evaluation.update_attributes(params[:evaluation])
redirect_to [#evaluation.batch_subject, #evaluation]
end
In View
<table class="medium">
<thead>
<tr>
<th>name</th>
<th>Grade</th>
</tr>
</thead>
<tbody>
<%=f.fields_for :grades do |g|%>
<tr>
<td><%=g.label :value,g.object.student.full_name%> <%= g.hidden_field :student_id%></td>
<td><%=g.text_field :value%></td>
</tr>
<%end%>
</tbody>
</table>