Active record wont save for some reason - ruby-on-rails

Question

I have an model called assignment, which represents a rich join between users and questions in a multiple choice quiz app. when a user answers a question, the response is recorded in the following update method in the assignments controller
def edit
#assignment = Assignment.find_by_id(params[:id])
#user = #assignment.user
#question = #assignment.question
puts "user #{#user} question #{#question} assignment #{#assignment}"
end
def update
#assignment = Assignment.find(params[:id])
#user = #assignment.user
#assignment.update_attributes(:response => params[:assignment][:response])
if #assignment.save
flash[:notice] = "Your response has been saved"
redirect_to(:action => 'show', :id => #assignment.id , :user_id => #user.id)
else
puts #assignment.save
puts "could not save"
render(user_assignment_path(#user, #assignment) , :html => {:method => :get})
end
end
I have a before save called grade that gets called. Here is the model:
class Assignment ActiveRecord::Base
belongs_to :user
belongs_to :question
attr_accessible :title, :body, :user_id, :question_id , :response
before_save :grade
def grade
self.correct = (response == self.question.solution) unless response == nil
end
end
So the first time I submit a response, the save works perfectly and it redirects me accordingly. after that, if i try to edit the question again and resubmit the form, the save fails.
Can anyone think of a reason this might be occurring?
In addition I know there is an error in the second redirect, so if someone could correct my usage that would be a bonus help
EDIT Here is the Edit erb, in case someone can spot something wrong here. I also added the edit method in the controller above.
<div class="admin-display">
<%if #admin%>
<p>
You may edit the user's response below or change the question to override whether the question is marked correct.
</p>
<%end%>
</div>
<div class="question body">
<%= #question.question %>
</div>
<div class="answer-choices">
<%= params[:user_id] + " " + params[:id] %>
<ol type="A">
<%=form_for(#assignment , :url => user_assignment_path(params[:user_id] , params[:id]) , :html => {:method => "put"}, :user_id => params[:user_id]) do |f|%>
<%[#question.answerA, #question.answerB ,#question.answerC ,#question.answerD].each do |choice|%>
<li>
<%= f.radio_button(:response, choice)%>
<%= choice %>
</li>
<%end%>
</ol>
<div class="form-buttons">
<%= submit_tag("Submit Response") %>
</div>
<%end%>
</div>
EDIT 2 I have just gone through the steps by hand in the rails console, without any issue, so there must be something strange going on.

Answer 1

It's probably due to the fact that your grade() callback method is returning a false, which will cancel the action all together (as stated in the documentation).

Answer 2

Hope this will work for you.
In Assignment model, add correct field as attr_accessible. First time as the response is nil, it is not executing the statement in before_save method, Hence your code will be
class Assignment ActiveRecord::Base
belongs_to :user
belongs_to :question
attr_accessible :title, :body, :user_id, :question_id , :response, :correct
before_save :grade
def grade
correct = (response == question.solution) unless response.nil?
end
end
and cotroller action could be
def update
#assignment = Assignment.find(params[:id])
#user = #assignment.user
#assignment.update_attributes(:response => params[:assignment][:response])
if #assignment.valid?
flash[:notice] = "Your response has been saved"
redirect_to(:action => 'show', :id => #assignment.id , :user_id => #user.id)
else
render(user_assignment_path(#user, #assignment) , :html => {:method => :get})
end
end