Document SetNull validation introduced in [email protected]

[jkomyno]

In the "Referential Actions" page, we should mention that, starting from [email protected], defining a Prisma schema with a SetNull referential action referencing a non-nullable field is no longer valid.

Consider the following Prisma models:

model SomeUser {
  id      Int      @id
  profile Profile?
}

model Profile {
  id     Int      @id
  user   SomeUser @relation(fields: [userId], references: [id], onUpdate: SetNull, onDelete: SetNull)
  userId Int      @unique
}

The @relation in Profile is not valid anymore, as the referenced field (user_id) has a non-nullable type (Int).

We have decided to add this new Prisma validation as, with the scenario above, all databases would fail with a validation error at the database level (which would result in a Prisma migration error). The only exception is Postgres, which accepts SET NULL referential actions, but would fail at runtime once such action is triggered by a change in a referenced row.

The new validation error message is:

Error parsing attribute "@relation": The onUpdate referential action of a relation must not be set to SetNull when a referenced field is required.
Either choose another referential action, or make the referenced fields optional.

Here's an example of a valid Prisma schema using SetNull appropriately:

model SomeUser {
  id      Int      @id
  profile Profile?
}

model Profile {
  id     Int       @id
  user   SomeUser? @relation(fields: [userId], references: [id], onUpdate: SetNull, onDelete: SetNull)
  userId Int?      @unique
}

Please check out the internal notion for additional context.