Validations on parent and accepts_nested_attributes_for don't comply?


I've got two models:

class ProductGroup < ActiveRecord::Base    has_many :fields, :dependent => :destroy    accepts_nested_attributes_for :fields end

class Field < ActiveRecord::Base    belongs_to :product_group    validates_presence_of :product_group end

Now when I try something like this: ProductGroup.create(:title => "foo", :fields_attributes => {"new_1" => {:title => "bar"}}) it'll fail because of the validates_presence_of :product_group validation. Since the field is being build by the function (in assign_nested_attributes_for_collection_association of the NestedAttributes module) the product reference of field is not set because the ProductGroup instance is not saved yet, and hence the validation fails.

Now if I remove the validation all goes well and both objects are saved as they should.

Is there a better / other way to make sure a Field can only be saved when it has a reference to a ProductGroup while still being able to use the nested attributes functionality?