Call a model method in a partial called from another model

Question

I am having trouble calling a method in a partial. The method is defined in the Isbn model. Here's the set up:

Contracts

has_many :isbns, :through => :istcs

Isbns

belong_to :contracts

The Isbn show view successfully displays the result of roy_first, an instance variable that's defined in the method:

<% @isbn.roy_first.each do |hash| %>
<% hash.each do |channel, roy| %>
<%= "#{channel} 1st: £#{roy}" %> 
<% end %><% end %>

As I say, roy_first is an instance variable defined in Isbn.rb:

def sales_lookup_complete
# a bunch of code... 
@roy_first << {channel_name => ra = df*(u/100)}
end 

Here's the isbns_controller show, if it's relevant:

 @isbn.sales_lookup_complete

But when I try to call the same instance variable in an _isbn partial, I get an undefined method error. I get this error when I use a local or an instance variable.

My question: How do I call the same in a partial which is accessed from contracts > show.html.erb?

The partial is called from the contracts show page like this:

<%= render @isbns %>

Many thanks in advance.

Here is some more code as requested:

The contracts controller show method:

  def show
    @title = (@contract.contract_name + "'s contract")
    @istcs = @contract.istcs.paginate(:page => params[:page])
    @isbns = @contract.isbns.paginate(:page => params[:page])    
  end

The isbns controller show method:

  def show
    @isbn   = Isbn.find(params[:id])
    @title  = @isbn.descriptivedetail_titledetail_titleelement_titlewithoutprefix
    @sales  = @isbn.sales.paginate(:page => params[:page] || 1)
    @isbn.sales_lookup_complete
  end

The contract show view:

<h4>ISBNs <span class="add"><%= link_to "Create ISBN", new_isbn_path %></span></h4>
<% unless @contract.isbns.empty? %>
<table summary="Contract ISBNs">
<%= render @isbns %>        
    </table>
<% end %>

The isbn show view:

<table> 
    <tr><h5>Royalties for all sales</h5>
        <tr><% @isbn.roy_first.each do |hash| %>
            <td><% hash.each do |channel, roy| %>
                <%= "#{channel} 1st: £#{roy}" %> 
            </td><% end %><% end %>
        </tr>
</table>

This is the bit that causes the error, in the partial called _isbn, and which is in the isbn views area, but called from the contracts show view:

 Id: <%= isbn.id%>
<tr><% @isbn.roy_first.each do |hash| %>
    <td><% hash.each do |channel, roy| %>
        <%= "#{channel} 1st: £#{roy}" %> 
    </td><% end %><% end %>
</tr>

The isbn.id bit works fine. The code in tags gives the following error:

NoMethodError in Contracts#show

Showing /app/views/isbns/_isbn.html.erb where line #6 raised:

undefined method `roy_first' for nil:NilClass

Extracted source (around line #6):

3:  <span class="content"><%= link_to isbn.descriptivedetail_titledetail_titleelement_titlewithoutprefix, edit_isbn_path(isbn.id) %> </span>
4:     <span class="timestamp">
5:      Id: <%= isbn.id%>
6:      <tr><% @isbn.roy_first.each do |hash| %>
7:          <td><% hash.each do |channel, roy| %>
8:              <%= "#{channel} 1st: £#{roy}" %> 
9:          </td><% end %><% end %>

And making it a local variable gives:

NoMethodError in Contracts#show

Showing /app/views/isbns/_isbn.html.erb where line #6 raised:

You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.each

Extracted source (around line #6):

3:  <span class="content"><%= link_to isbn.descriptivedetail_titledetail_titleelement_titlewithoutprefix, edit_isbn_path(isbn.id) %> </span>
4:     <span class="timestamp">
5:      Id: <%= isbn.id%>
6:      <tr><% isbn.roy_first.each do |hash| %>
7:          <td><% hash.each do |channel, roy| %>
8:              <%= "#{channel} 1st: £#{roy}" %> 
9:          </td><% end %><% end %>

Trace of template inclusion: app/views/contracts/show.html.erb

Answer 1

I dont know if you are trying to do this, but try this:

contracts_controller - show

def show
  @title = (@contract.contract_name + "'s contract")
  @istcs = @contract.istcs.paginate(:page => params[:page])
  @isbns = @contract.isbns.paginate(:page => params[:page])    
end

contracts - show view

<h4>ISBNs <span class="add"><%= link_to "Create ISBN", new_isbn_path %></span></h4>
<% unless @isbns.empty? %>
  <table summary="Contract ISBNs">
    <% @isbns.each do |isbn| %>
      <% isbn.sales_lookup_complete %>
      <%= render :partial => "isbn", :locals => {:isbn => isbn} %>
    <% end %>       
   </table>
<% end %>

and _isbn.html.erb

<tr>
  <% isbn.roy_first.each do |hash| %>
    <td>
      <% hash.each do |channel, roy| %>
        <%= "#{channel} 1st: £#{roy}" %> 
      <% end %>
    </td>
  <% end %>
</tr>

Answer 2

In the _isbn.html.erb partial:

<% isbn.roy_first.each do |hash| %>
  <% hash.each do |channel, roy| %>
    <%= "#{channel} 1st: £#{roy}" %> 
  <% end %>
<% end %>

this should definitely work.

The error occurred while evaluating nil.each this error mean that roy_first method returns nil instead of expected hash.