How to create a dynamic select list using Simple Form and Awesome Nested Set in Rails 3.1? -

could please explain how create dynamically generated pull-down select shows name labels web visitor , writes corresponding id database? concept seems basic must obvious else @ wit's end trying find way make work and/or code example learning how this. suggestions frustrated newbie?

i have simple category model using awesome nested list track 200 categories. these table fields:

t.string :name t.integer :parent_id t.integer :lft t.integer :rgt 

this category.rb model:

class category < activerecord::base   acts_as_nested_set   attr_accessible :name, :parent_id end 

this simple form view/categories/_form.html.erb

<%= simple_form_for(@category) |f| %>   <%= f.error_notification %>    <div class="form-inputs">     <%= f.input :name, :label => 'category name' %>     <%= f.select :parent_id, :label => 'parent category', :value_method => { |r| [r.name, r.id, { :class => r.category.id }]}, :include_blank => true %>   </div>    <div class="form-actions">    <%= f.button :submit %>   </div> <% end %> 

this yields "syntaxerror in categories#new" error message

extracted source (around line #6):  3:  4:   <div class="form-inputs"> 5:     <%= f.input :name, :label => 'category name' %> 6:     <%= f.select :parent_id, :label => 'parent category', :value_method => { |r| [r.name, r.id, { :class => r.category.id }]}, :include_blank => true %> 7:   </div> 8:  9:   <div class="form-actions"> 

you can use awesome_nested_set's view helper building select:

<%= f.select :parent_id, nested_set_options(category, @category) {|i| "#{'-' * i.level} #{i.name}" } %>