In Prisma 4.6.0, changing `onDelete: SetNull` to `Cascade` results in recreating foreign key

Discussed in https://github.com/prisma/prisma/discussions/16223

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^{Originally posted by jameyhart November 10, 2022} @janpio After upgrading to 4.6.0, we started reciving the following error when migrating our database:

Error: Schema validation error - Error (query-engine-node-api library)
Error code: P1012
error: Error parsing attribute "@relation": The `onDelete` 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.

  -->  schema.prisma:126
   |
125 |     
126 |     survey    Survey   @relation(fields: [surveyId], references: [id], onDelete: SetNull)
127 |
   |

To rectify this, we changed the onDelete from SetNull to Cascade but it then cerates a new migration that drops the foreign key and recreates it. Is this the expected behaviour?

Our current database model:

model Survey {
    id                      String                    @id @default(cuid())
    name                    String
    survey                  Json
    reportSurvey            SurveyReport[]
    ...
}

model SurveyReport {
    id                String       @id @default(cuid())
    surveyId          String
    survey            Survey       @relation(fields: [surveyId], references: [id], onDelete: SetNull)
    reportType        SurveyReportType
    ...
}

The output from the new migration:

-- DropForeignKey
ALTER TABLE "SurveyReport" DROP CONSTRAINT "SurveyReport_surveyId_fkey";

-- AddForeignKey
ALTER TABLE "SurveyReport" ADD CONSTRAINT "SurveyReport_surveyId_fkey" FOREIGN KEY ("surveyId") REFERENCES "Survey"("id") ON DELETE CASCADE ON UPDATE CASCADE;

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[jameyhart]

Hi both, thanks for the speedy reply!

So, upgrading to v4.6.1 fixed the bug we were experiecing with enums. Yes, the schema was written by hand. The new validation helped us highlight an issue/oversight from us in the schema, i.e. we were trying to set the Survey field to NULL if a survey was deleted, however the field cannot be NULL as it’s required. So that’s appreciated.

Also, yes - everything you said makes sense. I’ve discussed with the team and we’re happy for you to close this issue and we’ll review both our Prisma versions and our database models going forward.

Thanks so much!

[elie222]

4.6.1 also fixed the enum error for us. 4.6.0 caused the problem.