Creating or deleting associations with accepts_nested_attributes_for

Question

I have 2 models, Category and LineItemTypes

There are already plenty existing of both, it is now a requirement for them to be associated. Being many LineItemTypes for every Category.

I have added accepts_nested_attributes_for :line_item_types on Category

I've tried using a hidden_field on a form to create a list of existing associated LineItemTypes:

- form_for @category do |form|
  %ul#categorised
    - form.fields_for :line_item_types do |line_item_types|
      -categorised.each do |l|
        %li
          =l.description
          =line_item_types.hidden_field :category_id

  =form.submit

If I add an item to that list, I get errors saying that a LineItemType for that Category can't be found. I thought accepts_nested_attributes_for would add the association if it doesn't exist. Or is it only for 'creating' new records and modifying existing relationships, not creating new relationships.

a.update_attributes({:line_item_types_attributes => [{:id => 2767}, {:id => LineItemType.find(2).id}]})
ActiveRecord::RecordNotFound: Couldn't find LineItemType with ID=2 for Category with ID=1

Any ideas without having to write something to traverse the resulting form params and create the associations? Or an even easier way to achieving this?

Answer 1

I've come to the conclusion that accepts_nested_attributes_for works kinda like url_for... Where the presence of ID makes it assume the relationship exists. Rendering accepts_nested_attributes_for not suitable for what I want to do.

I've worked around this with a before filter:

def find_line_item_types
  params[:category][:line_item_types] = LineItemType.find(params[:category][:line_item_types].collect { |a| a[0].to_i }) if params[:category] and params[:category][:line_item_types]
end

Answer 2

no you should be able to create line_item_types from a Category instance without specifying the category_id in the line_item_types attributes!

You should check that you got the :inverse_of option in your has_many and belongs_to declarations.

# in Category
has_many :line_item_types, :inverse_of => :category

# In LineItemType
belongs_to :category, :inverse_of => :line_item_types

Tell me if that helps.

Answer 3

Well, I had the same issue, so I searched into the source and monkey patched accepts_nested_attributes_for to allow this behavior...

https://gist.github.com/2223565

It looks like a lot, but I actually just modified a few lines:

module ActiveRecord::NestedAttributes::ClassMethods
  def accepts_nested_attributes_for(*attr_names)
    # ...
    #options.assert_valid_keys(:allow_destroy, :reject_if, :limit, :update_only)
    options.assert_valid_keys(:allow_destroy, :reject_if, :limit, :update_only, :allow_existing)
    # ...
  end
end

And...

module ActiveRecord::NestedAttributes
  def assign_nested_attributes_for_collection_association(association_name, attributes_collection, assignment_opts = {})
    # ...
    #existing_records = if association.loaded?
    #  association.target
    #else
    #  attribute_ids = attributes_collection.map {|a| a['id'] || a[:id] }.compact
    #  attribute_ids.empty? ? [] : association.scoped.where(association.klass.primary_key => attribute_ids)
    #end

    existing_records = if options[:allow_existing] or not association.loaded?
      attribute_ids = attributes_collection.map {|a| a['id'] || a[:id] }.compact
      scope = options[:allow_existing] ? association.target_scope : association.scoped
      scope.where(association.klass.primary_key => attribute_ids)
    else
      association.target
    end
    # ...
  end
end