edgedb error: ConstraintViolationError: may not make non-empty object type 'default::Person' abstract

[passion8]

I am reading a book, I am on chapter 2 https://www.edgedb.com/easy-edgedb/chapter2

when I read scalar type Transport extending enum<Feet, Train, HorseDrawnCarriage>; , I made appropriate changes into the schema (below is the schema)

 module default {
    
    abstract type Person {
      required property name -> str;
      multi link places_visited -> City;
    }
    
    scalar type Transport extending enum<Feet, Train, HorseDrawnCarriage>;
  
    type PC extending Person {
      required property transport -> Transport;
    }
  
    type NPC extending Person {
    }
  
    type City {
      required property name -> str;
      property modern_name -> str;
      property important_places -> array<str>;
    }
  
  }

after then I ran edgedb migration create and edgedb migrate it is throwing error

edgedb error:  ConstraintViolationError: may not make non-empty object type 'default::Person' abstract

What does it mean? How to solve it?

I am attaching migrations, which probably might help you to debug.

migrations.zip

[elprans]

Turning a non-abstract Person type into an abstract one while it contains data is not allowed, because abstract types are not supposed to contain data.

Two ways to fix this:

1. Migrate to an empty schema first.
2. Remove all data from Person before migrating: delete Person (though this may fail if there are links to person objects).

@vpetrovykh, can we do something here to remove this snag?

P/S @passion8, also please direct future book bugs to the edgedb/easy-edgedb repo. Thanks!

[dotlouis]

Just in case someone stumbles upon this while migrating, here's a relevant discord thread to help: https://discord.com/channels/841451783728529451/1009476546085523496/1009499950054396026