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Unique constraint error inside a transaction throws unparsed error (but works fine when using Node API)

See original GitHub issue

Bug description

While trying to auto-generate slugs for user-made pages at Copyfolio, we noticed that unique constraint violation errors aren’t caught properly inside a prisma.$transaction.

How to reproduce

Have a model with a unique constraint, e.g. a Site with a globally unique URL slug.
Run some code which is meant to detect unique slug constraint violation errors – and then auto-generate a new slug to try with, but that isn’t part of the code below:

/* Fill our database with some initial data */
await prisma.site.create({ id: "1", slug: "taken-by-1" });
await prisma.site.create({ id: "2", slug: "another" });

try {
  await prisma.$transaction([
    prisma.site.updateMany({
      where: { id: "2" },
      data: { slug: "taken-by-1" },
    }),

    /* Any other site update is required for the test to fail */
    prisma.site.update({
      where: { id: "2" },
      data: { id: "2" },
    }),
  ]);
} catch (error) {
  if (
    error instanceof PrismaClientKnownRequestError &&
    error.code === "P2002"
  ) {
    console.debug("Unique constraint violation detection works");
  } else {
    console.error("Unknown error, as violation detection fails");
    throw error;
  }
}

It should throw an unknown error, which isn’t the expected behavior. However, then using previewFeatures = ["nApi"], the code above works as expected.

Expected behavior

No response

Prisma information

model Site {
  id   String @id @default(cuid())
  slug String @unique
}

Environment & setup

OS: mac OS v11.4
Database: PostgreSQL 12/13
Node.js version: v14.16.1

Prisma Version

prisma               : 2.23.0
@prisma/client       : 2.23.0
Current platform     : darwin
Query Engine         : query-engine adf5e8cba3daf12d456d911d72b6e9418681b28b (at node_modules/@prisma/engines/query-engine-darwin)
Migration Engine     : migration-engine-cli adf5e8cba3daf12d456d911d72b6e9418681b28b (at node_modules/@prisma/engines/migration-engine-darwin)
Introspection Engine : introspection-core adf5e8cba3daf12d456d911d72b6e9418681b28b (at node_modules/@prisma/engines/introspection-engine-darwin)
Format Binary        : prisma-fmt adf5e8cba3daf12d456d911d72b6e9418681b28b (at node_modules/@prisma/engines/prisma-fmt-darwin)
Default Engines Hash : adf5e8cba3daf12d456d911d72b6e9418681b28b
Studio               : 0.393.0