I’m trying to set up a couple of validations – unclear what the best approach is:

    attribute :allowed_types, {:array, :atom} do
      allow_nil? false
      default [:value_add, :non_value_add]
    end

    attribute :default_type, :atom do
      allow_nil? false
    end

  validations do
    # this works but is clunky (what if allowed set is > 2?)
    validate one_of(:allowed_types, [[:value_add, :non_value_add], [:value_add], [:non_value_add]])
    # this doesn't work ... :allowed_types is supposed to be an attribute, not an atom... :/
    validate one_of(:default_type, [:allowed_types])
  end

Potentially pretty obvious, but the intention of the two validations:

1. The first is to make sure the :allowed_types conforms to some combination of one or more of a set (currently, just [:value_add, :non_value_add])
2. The second is to make sure that the value of :default_type is one of the types specified in the attribute :allowed_types

I can live with #1 for now (until the list grows, but then it becomes a problem). #2 seems like it may require a custom validation, but I’m unsure if that’s correct… or how to write one quite yet…