Rails: Iterate through attributes with simple_form

Question

I have a rails model with a large number of fields (112), for loading a configuration. I would like, in the edit and show forms, display only if the field is already filled . That is, if the field is null in the database then do not display it for edit.

There are two records - the main one is Batch and there is a 1:1 relationship to the Primer3Batch class. I'm trying to do an edit on the Primer3Batch class on the show action of Batch, I'm not sure if this is a good idea or will even work.

I have tried using the attributes method and am getting this error:

undefined method `attributes' for #<SimpleForm::FormBuilder

batches_controller.rb

def show
  @batch = Batch.find(params[:id])
  @primer3 = Primer3Batch.where(:batch_id => @batch.id)[0]

  respond_to do |format|
    format.html # show.html.erb
    format.json { render json: @batch }
  end
end

batches/show.html.erb

<h1>Batch Details: <%= @batch.id %></h1>

<%= simple_form_for(@primer3) do |f| %>
  <%= f.error_notification %>

  <div class="form-inputs">
    <% f.attributes.each_attribute do |a| %>
      <% if a %><%# if a is not nil %>
        <%= f.input a %><%# send the field to the form %>
      <% end %>
    <% end %>
  </div>

  <div class="form-actions">
    <%= f.button :submit %>
  </div>
<% end %> 

EDIT

Thank you JSWorld for pointing out the error of using the instance variable. I have corrected it and seem to have gotten further but it's still not quite right. This is the line changed - note attributes.each as attributes.each_attribute doesn't work.

<% @primer3.attributes.each do |a| %>

Now I am getting an error on the form fields:

undefined method `["id", 110]' for #<Primer3Batch:

I guess I need to somehow turn this :

a   ["id", 110]

into:

<%= f.input :id %>

* EDIT 2 *

Final code block based on IIya Khokhryakov's answer.

<%= simple_form_for(@primer3) do |f| %>
  <%= f.error_notification %>

  <div class="form-inputs">
    <% @primer3.attributes.each_pair do |name, value| %>
      <%= f.input name if value %>
    <% end %>
  </div>

  <div class="form-actions">
    <%= f.button :submit %>
  </div>
<% end %>

Answer 1

I hope your intention is @primer3.attributes and not f.attributes . The error is because f is the form object and does not have attributes associated with it.

Answer 2

@primer3.attributes is a Hash of the model's attributes and their values. So you can do something like this:

<% @primer3.attributes.each_pair do |name, value| %>
  <%= f.input name if value %>
<% end %>