How to loop through two alternating resources on a

Question

I'm trying to make a dynamic form of questions and answers, like so:

Question _______

Answer _______

Question _______

Answer _______

I can't figure out how to loop through the two resources as alternating pairs. I have tried this:

<%= semantic_fields_for [@question, @answer] do |h, i| %>
  <%= f.inputs :for => @question do |h|%>
    <%= h.input :question %>
  <% end %>
  <%= f.inputs :for => @answer do |i|%>
    <%= i.input :answer %>
  <% end %>
<% end %>

But it gives me the error "Undefined method `model_name' for Array:Class."

My controller:

def new

  @post = Post.new
  @question = @post.questions.new
  @answer = @question.build_answer

  respond_to do |format|
    format.html
  end
end

And my models:

class Post < ActiveRecord::Base
  has_many :questions
  has_many :answers
end
class Question < ActiveRecord::Base
  belongs_to :post
  has_one :answer
end
class Answer < ActiveRecord::Base
  belongs_to :question
  belongs_to :post
end

Answer 1

I think what you need is exactly what is described in these railcasts:

• Nested Model Form Part 1
• Nested Model Form Part 2

I think you should also refactor a bit, Posts should not have questions. You might notice a little difference from the railcasts but that's because you have only one answer per question whereas in the railcasts a question has many answers. In the part 2 it shows how to add AJAX calls to add/remove questions and answers (probably you won't need this if you only have one answer).

Mandatory reading so you have a better understanding of associations and how nested attributes work:

• A Guide to Active Record Associations
• Active Record Nested Attributes

And this is an example that will probably work, with some minimum tweaking. I haven't used semantic fields, just the standard form builder.

class Post < ActiveRecord::Base
  has_many :questions
  accepts_nested_attributes_for :questions, :reject_if => lambda { |a| a[:content].blank? }, :allow_destroy => true
end
class Question < ActiveRecord::Base
  belongs_to :post
  has_one :answer, :dependent => :destroy
  accepts_nested_attributes_for :answers, :reject_if => lambda { |a| a[:content].blank? }, :allow_destroy => true
end
class Answer < ActiveRecord::Base
  belongs_to :question
end

# posts_controller.rb
def new
  @post = Post.new
  # lets add 2 questions
  2.times do
    question = @post.questions.build
    question.build_answer

  respond_to do |format|
    format.html
  end
end

# views/posts/_form.html.erb
<%= form_for @post do |f| %>
  <%= f.error_messages %>
  <p>
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </p>
  <%= f.fields_for :questions do |builder| %>
    <%= render "question_fields", :f => builder %>
  <% end %>
  <p><%= f.submit "Submit" %></p>
<% end %>

# views/posts/_question_fields.html.erb
<p>
  <%= f.label :content, "Question" %><br />
  <%= f.text_area :content, :rows => 3 %><br />
  <%= f.check_box :_destroy %>
  <%= f.label :_destroy, "Remove Question" %>
</p>
<%= f.fields_for :answers do |builder| %>
  <%= render 'answer_fields', :f => builder %>
<% end %>

# views/posts/_answer_fields.html.erb
<p>
  <%= f.label :content, "Answer" %>
  <%= f.text_field :content %>
  <%= f.check_box :_destroy %>
  <%= f.label :_destroy, "Remove" %>
</p>

Answer 2

So I don't personally use formtastic but I understand it follows similar lines to simple_form. Your error is coming from trying to pass an Array to semantic_fields_for which only takes a single object:

<%= semantic_form_for @questions do |q| %>
  <%= q.input :question %>
  <%= q.semantic_fields_for @answer do |a| %>
    <%= a.inputs :answer %>
  <% end %>
  <%= q.actions %>
<% end %>

Don’t forget your models need to be setup correctly with accepts_nested_attributes_for

class Question < ActiveRecord::Base
  belongs_to :post
  has_one :answer
  accepts_nested_attributes_for :answers
end

You'll want to check out the formtastic docs at https://github.com/justinfrench/formtastic

That should get your form showing correctly in the view but you'll need to add some more to your questions controller to make sure it saves the answers (someone correct me if I'm mistaken).

Also just so it's clear do your Questions and Answers tables really have a question and answer column? If the columns are actually something like :body you'll want to replace the relevant symbols in the above code.