rails & mongoid - scroll through specific group of records

Question

I have a site implemented with Rails and mongoDB to submit, read and update items.
There are a few different areas on the site that you can view items and filter them based on search keywords or different querying methods.

For example: on the home page there is a list of categories to sort by. 'Use Case', 'Status', 'Level'. When a user clicks the 'Use Case' button a list will show up with more specific categories for use cases such as 'E-Commerce', if they click that a div will populate with the items that have a Use Case that equals E-Commerce. From this point on a specific item they can click a 'Details' button which will show them all the properties for the item.
In this 'detailed' view I have a next and back button. Right now it scrolls through the database of items by incrementing and decrementing the item ID number.
I want the next and back button to be able to scroll through the list they were presented with in the populated div. It's accessible by an instance variable called @items which is initialized in the items controller but can't be seen in the details view even when saved as a global variable...

The only option I have thought of is to pass the list of items through as a URL parameter - but that seems like a messy way to do it.
Is there any other way to pass an instance variable between different views?

Example code:

item_controller.rb :

 def list
   @items = Item.asc(:id)
 end

list.html.erb :

<tbody>
    <% @items.each do |item| %>
            <% $list = @items%>
      <tr>
        <td><%= item.name %></td>
        <td><% item.Use_Cases.each do |u| %>
           <ul>
             <li><%= u %></li>
       </ul>
           <% end %>
        </td>

        <td><%= item.Level %></td>
        <td><%= item.Status %></td>
        <td><%= link_to item, class: 'btn btn-default' do %>
            <span class="glyphicon glyphicon-eye-open"></span>&nbsp;Details
            <% end %>
    </td>
      </tr>
    <% end %>
  </tbody>

show.html.erb - scroll buttons :

  <div class="panel-footer">
    <%if @item.id != @first_id %>
        <% #need to change to scroll to previous in $list %>
        <%= link_to item_path(:id => (@item.id-1)), class: 'btn btn-default' do %>
            <span class="glyphicon glyphicon-menu-left"></span>&nbsp;Back
        <% end %>
    <% end %>
    <%if @item.id != @last_id %>
        <% #need to change to scroll to next in $list %>
        <%= link_to item_path(:id => (@item.id+1)), class: 'btn btn-default' do %>
            Next&nbsp;<span class="glyphicon glyphicon-menu-right"></span>
        <% end %>
    <% end %>
  </div>

Answer 1

Use the same scope to retreive a list of items and a single item with its next and previous.

 # item_controller.rb     

 def list
   @items = items_scope
 end

def show
  @item = items_scope.find(params[:id])
  @next_item_id = items_scope.select(:id).where("id > ?", params[:id]).first
  @previous_item_id = items_scope.select(:id).where("id < ?", params[:id]).last
end

private

def items_scope
  # this scope might depend on url parameters which, for example, present current chosen category
  # `order("id ASC")` is a very important part. it makes this solution work
  Item.order("id ASC").any_other_scopes_or_conditions_depending_on_chosen_category
end

In the view:

<%= link_to item_path(:id => @next_item_id) ...
<%= link_to item_path(:id => @previous_item_id) ...