gistfile1.coffee

angular.module('product_size_resource', ['ngResource']).
factory 'ProductSize', ["$resource", ($resource) ->
  ProductSize = $resource '/product_sizes/:id', format: 'json']

app_module = angular.module 'products', ['product_size_resource']

app_module.controller "FormCtrl", ["$scope", "ProductSize", ($scope, ProductSize) ->
  $scope.product_references = window.product_references
  $scope.product_sizes = ProductSize.query()

  $scope.add = ->
    $scope.product_references.push({})

  $scope.remove = (index) ->
    $scope.product_references[index].deleted = true

    if($scope.product_references[index]._id)
      $scope.product_references[index].deleted_id = true

]

gistfile2.haml

:javascript
  window.product_references = #{f.object.product_references.to_json.html_safe};

= f.error_notification

= f.input :name

%div(ng-repeat="product_reference in product_references")
  %div(ng-if="!product_reference.deleted")
    .controls
      %label Reference:
      %input(type="text" ng-model="product_reference.code" name="product[product_references_attributes][][code]")
      %select(ng-model="product_reference.product_size_id" ng-options="s._id as s.name for s in product_sizes")
      %input(type="hidden" name="product[product_references_attributes][][product_size_id]" value="{{product_reference.product_size_id}}")

      %a(ng-click="remove($index)") Remove

  %input(ng-if="product_reference._id" type="hidden" name="product[product_references_attributes[][_id]" value="{{product_reference._id}}")
  %input(ng-if="product_reference.deleted_id" type="hidden" name="product[product_references_attributes[][_destroy]" value="true")

  %input(type="hidden" name="product[product_references_attributes[]" value="")
.control-group
  .controls
    %a(ng-click="add()") Add

.form-actions
  = f.button :submit

= custom_javascript "products/form"