Using nested_form_for with rails_admin

gistfile1.txt

class Product < ActiveRecord::Base

  has_many :material_product_mappings, :dependent => :destroy, :inverse_of => :product
  has_many :materials, :through => :material_product_mappings, :autosave => true

  #...

  rails_admin do
    list do
      field :material_product_mappings do
        label "Materials"
        visible true
      end
      #...
    end
    edit do
      form_builder :nested_form_for
      field :material_product_mappings do
        label "Materials"
        partial "edit_material_product_mappings"
      end
      #...
    end
  end

end

class MaterialProductMapping < ActiveRecord::Base
  belongs_to :product, :inverse_of => :material_product_mappings
  belongs_to :material, :inverse_of => :material_product_mappings
  
  validates :num_units,
  :numericality =>  { :greater_than_or_equal_to => 0 }

  def name
    "#{self.material.name} (#{self.material.unit.name}) x #{self.num_units}"
  end

  rails_admin do
    label "Materials"
    visible false
  end
end


# file .../app/views/rails_admin/main/_edit_material_product_mappings.html.erb

<div class="field <%= field.dom_id %>">
  <% _saved_object = @object %>
  <% _saved_form = form %>
  <% _saved_field = field %>
  <%= label_tag(field.dom_id, field.label) %>
  <div style="clear:left;padding-left:100px">
    <%= form.fields_for(:material_product_mappings) %>
    <p>
      <%= form.link_to_add('Add Material ', :material_product_mappings) %>
    </p>
    <% @object = _saved_object %>
    <% form = _saved_form %>
    <% field = _saved_field %>
    <% if field.has_errors? %>
      <span class="errorMessage"><%= "#{field.label } #{field.errors.first}" %></span>
    <% end %>
  </div>
</div>

# file .../app/views/rails_admin/main/_material_product_mapping_fields.html.erb
#  nested form looks for this file...
<% ff = f %>
<% ff.object.errors.full_messages.each do |msg| %>
   <p class="flash_alert_msg"><%= msg %></p>
<% end %>
<%= ff.number_field(:num_units, :min => 0.0, :step => 0.01, :size => 6, :style => "text-align:right") %>
<%= ff.collection_select('material_id',Material.active,:id,:name,:prompt => false) %>
<%= ff.link_to_remove('Remove') %>

# also need to copy app/views/layouts/rails_admin/_head.html.haml from the rails_admin installation to
#  your app and modify it to include nested_form's JS. add the following line:

    - head_javascript "nested_form"