has_one_association.rb

require 'rails_admin/config/fields/association'

module RailsAdmin
  module Config
    module Fields
      module Types
        class HasOneAssociation < RailsAdmin::Config::Fields::Association
          # Register field type for the type loader
          RailsAdmin::Config::Fields::Types::register(self)

          register_instance_option :partial do
            nested_form ? :form_nested_one : :form_filtering_select
          end

          # Accessor for field's formatted value
          register_instance_option :formatted_value do
            (o = value) && o.send(associated_model_config.object_label_method)
          end

          register_instance_option :inline_add do
            true
          end

          register_instance_option :inline_edit do
            true
          end


          def editable?
            (nested_form || abstract_model.model.new.respond_to?("#{self.name}_id=")) && super
          end

          def selected_id
            value.try :id
          end

          def method_name
            nested_form ? "#{self.name}_attributes".to_sym  : "#{self.name}_id".to_sym
          end

          def multiple?
            false
          end
        end
      end
    end
  end
end