Members' uniqueness

[awead]

I don't know if this is in scope or not, but the use case I'm dealing with is that members of a PCDM object must be unique according to a given property. For example, no two objects can be members of another object if they have the same value for a given property.

Given:

class List < ActiveFedora::Base
  include Hydra::PCDM::ObjectBehavior
end

class ListItem
  include Hydra::PCDM::ObjectBehavior
  property :pref_label, predicate: ::RDF::SKOS.prefLabel, multiple: false
end

Doing something like this should not be allowed:

> list = List.create
> list.members << ListItem.create(pref_label: "Duplicate")
> list.members << ListItem.create(pref_label: "Duplicate")

It might be helpful to have something like:

class List < ActiveFedora::Base
  include Hydra::PCDM::ObjectBehavior
  validate_uniqueness_of_member with: :pref_label
end

But, not sure if that's appropriate or even possible here.