Make the implicit unique constraints on 1:1 relations explicit

[tomhoule]

Problem

The following Prisma schema:

model A {
  id   Int @id
  b_id Int
  b    B @relation(fields: [b_id], references: [id])
}

model B {
  id Int @id
  as A?
}

doesn't contain an @unique, but if you migrate it, you will have a unique index on b_id so that it's enforced that the relation is really one-to-one and not one-to-many. If you introspect it, it would become explicit in the schema. This is a very old opinionation. Prisma as a whole has evolved towards more explicitness, less "magic" in the schema to better reflect the reality of the database.

This issue is here to propose that we enforce that the backing scalar fields of the relation are covered by a unique constraint, meaning we would validate (and possibly help with autoformatting or code actions) so that the valid schema would be:

model A {
  id   Int @id
  b_id Int @unique
  b    B   @relation(fields: [b_id], references: [id])
}

model B {
  id Int @id
  as A?
}

This works exactly the same if the relation is backed by multiple scalar fields.

Suggested solution

1. Add a validation with a clear error message explaining that to enforce the one-to-one-ness of the relation, a unique constraint is required on such and such fields, with an example of how it would look like.
2. Offer a code action to do this automatically in LSP-enabled editors.

This is a breaking change, because existing valid Prisma schemas would not pass validation anymore. It can only be released in a new major version.

Alternatives

• Do nothing and keep the current behaviour.
• Make explicating the unique constraint part of the reformatting logic

Additional context

• Prisma internal document

[janpio]

Client team label as this will trigger work in fixing QE tests.

[janpio]

Note: This is not for implementation, but only consideration what to do about it next.

[BroNils]

any solution for this? i don't have much time to wait for prisma4 got released

[janpio]

This only adds a restriction, you can just enforce that manually already - if there a 1:1 relation, make sure there is a @unique constraint.

[BroNils]

oh okay, thanks for your reply

…

On Thu, Jun 16, 2022, 9:00 PM Jan Piotrowski ***@***.***> wrote: This only adds a restriction, you can just enforce that manually already - if there a 1:1 relation, make sure there is a @unique constraint. — Reply to this email directly, view it on GitHub <#10503 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AEVOVPFSGWKRSEWUAPQR7OTVPMXOZANCNFSM5JBBJ77Q> . You are receiving this because you commented.Message ID: ***@***.***>