Collection of Models for Red

Collection AB {
  model B is table<bbb> { ... }
  model A is table<aaa> { has UInt $.id is serial; has B @.bs is relationship{ .a-id } }
  model B { has UInt $.id is serial; has UInt $.a-id is referencing{ A.id }; has A $.a is relationship{ .a-id } }
}