Generate and associate type information for domain elements

[subhashb]

Having type information available for elements like Aggregates, Entities, and Events is invaluable. While this works in most cases, some edge scenarios need to be handled:

• Type information for elements subclassing an abstract base element, like HoldExpired and HoldPlaced event classes below:

  @lending.event(part_of="Patron", abstract=True)
  class HoldEvent:
      patron_id = Identifier(required=True)
      patron_type = String(required=True)
      hold_id = Identifier(required=True)
      branch_id = Identifier(required=True)
      book_id = Identifier(required=True)
      hold_type = String(required=True)
      requested_at = DateTime(required=True)
      expires_on = Date()
  
  
  @lending.event(part_of="Patron")
  class HoldExpired(HoldEvent):
      """Event raised when a hold on a book placed by a patron expires"""
  
  
  @lending.event(part_of="Patron")
  class HoldPlaced(HoldEvent):
      """Event raised when a book is placed on hold"""
  

• Auto-generated fields like id and attributes/shadow fields backing associations and value objects

• Special fields like HasMany and ValueObject that are connected to other elements have to be annotated with the proper types and attributse