get_real.rb

class State < ActiveRecord::Base
  has_many :case_type_states
  has_many :case_types,    :through => :case_type_states
  has_many :process_types, :through => :case_type_states
  
  def case_type_processes=(hash)
    hash.each do |case_type_id, process_type_ids|
      case_type_states.create!(:case_type_id => case_type_id,
                               :process_type_ids => process_type_ids)
    end
  end
end

class CaseTypeState < ActiveRecord::Base
  belongs_to :state
  belongs_to :case_type
  
  has_and_belongs_to_many :process_types
end

# case_type_state_process_types JOIN table (no primary key)
# case_type_state_id, process_type_id

class CaseType < ActiveRecord::Base
end

class ProcessType < ActiveRecord::base
end

case_type_a = CaseType.create!  # id => 1
case_type_b = CaseType.create!  # id => 2

process_type_a = ProcessType.create!  # id => 1
process_type_b = ProcessType.create!  # id => 2

state = State.new(:case_type_processes => {
                     "1" => [2],
                     "2" => [1]
                  })