Displaying an explicit number of nested attributes in a Rails form

Given three models:

1. Document
2. Asset
3. AssetCategory

A document accepts_nested_attributes_for assets (a document has_many assets), and an asset belongs_to an asset category.

I would like to display a field for an asset attribute for each asset category.

I am currently achieving this as follows. Controller:

def new
  @document = Document.new
  @asset_categories = AssetCategory.all
  @asset_categories.count.times { @document.assets.build }
end

View (this example uses the semantic_fields_for method provided by Formtastic, but this is just a thin wrapper around fields_for):

i=0
f.semantic_fields_开发者_开发技巧for :assets do |asset_form|
  asset_form.input :attachment, :label => @asset_categories[i].name
  asset_form.input :asset_category, :as => :hidden, :value => @asset_categories[i].id
  i+=1
end

Is there a cleaner approach to this? I'm not so fond of the temporary variable i.

In the controller:

def new
  @document = Document.new
  AssetCategory.all.each do |ac|
    @document.assets.build :asset_category_id=>ac.id
  end
end

In the view:

f.semantic_fields_for :assets do |af|
  af.input :attachment, :label=>af.object.asset_category.name
  af.input :asset_category_id, :as => :hidden, :value => af.object.asset_category.id
end