[Breaking Change] Foreign key for 1:n moved to another table.

[sameoldmadness]

Given a schema

model Merchant {
  id    String    @default(cuid()) @id
}

model Payload {
  id                   String           @default(cuid()) @id
  merchant .   Merchant?
}

When I update to preview15
And create a migration
I see a breaking change

ALTER TABLE "public"."Merchant" DROP COLUMN "Payload;

ALTER TABLE "public"."Payload" ADD COLUMN "merchant" text   REFERENCES "public"."Merchant"("id") ON DELETE SET NULL;

Expected behaviour: be able to perform this migration without a data loss.

[tomhoule]

Thanks for reporting this :)

This migration was probably caused by a change we made recently in how prisma interprets "implicit self-relations" like the relation between Merchant and Payload in your schema. Relevant links: spec, PR.

And you are right, the current behaviour is leading to systematic data loss when doing that type of schema changes. We haven't had the time and resources to implement something better yet, but we are very much aware of that and are planning to work on it. Discussion is centralized here.