datamapper multi-field unique index

Question

In Datamapper, how would one specify the the combination of two fields must be unique. For example categories must have unique names within a domain:

class Category
  include DataMapper.resource
  property :name, String, :index=>true #must be unique for a given domain

  belongs_to :domain
end

Answer 1

You have to create a unique index for the two properties:

class Category
  include DataMapper::Resource

  property :name, String, :unique_index => :u
  property :domain_id, Integer, :unique_index => :u

  belongs_to :domain
end