Wrong nullable types with fluent API in Prisma 5.0

[p-kuen]

Bug description

We use Fluent API very often and it works very well.
Since Prisma version 5.0, results for related models queried with fluent API are nullable, although findUniqueOrThrow was used on the base model and the relation field is not optional.

How to reproduce

1. Create two models with a 1:n relation:

model PlanGroup {
  id             Int                     @id @default(autoincrement()) @db.UnsignedInt
  plans          BuildingSitePlan[]
}

model Plan {
  id              Int         @id @default(autoincrement()) @db.UnsignedInt
  groupId         Int         @map("group_id") @db.UnsignedInt
  group           PlanGroup   @relation(fields: [groupId], references: [id], onDelete: Cascade)
}

3. Use Fluent API to query them:

(
    await prisma.plan
      .findUniqueOrThrow({
        where: {
          id,
        },
      })
      .group({
        select: {
          id: true,
        },
        
      })
  ).id

6. See typescript error ts(2531) "Object is possibly null"

Expected behavior

In versions <5.0.0, queries for non-nullable related models with fluent api were non-nullable.

Prisma information

model PlanGroup {
  id             Int                     @id @default(autoincrement()) @db.UnsignedInt
  plans          BuildingSitePlan[]
}

model Plan {
  id              Int         @id @default(autoincrement()) @db.UnsignedInt
  groupId         Int         @map("group_id") @db.UnsignedInt
  group           PlanGroup   @relation(fields: [groupId], references: [id], onDelete: Cascade)
}

(
    await prisma.plan
      .findUniqueOrThrow({
        where: {
          id,
        },
      })
      .group({
        select: {
          id: true,
        },
        
      })
  ).id

Environment & setup

• OS: macOS Ventura 13.2
• Database: MariaDB 10.11.3
• Node.js version: v20.2.0

Prisma Version

prisma                  : 5.0.0
@prisma/client          : 5.0.0
Current platform        : darwin-arm64
Query Engine (Node-API) : libquery-engine 6b0aef69b7cdfc787f822ecd7cdc76d5f1991584 (at node_modules/.pnpm/@prisma+engines@5.0.0/node_modules/@prisma/engines/libquery_engine-darwin-arm64.dylib.node)
Schema Engine           : schema-engine-cli 6b0aef69b7cdfc787f822ecd7cdc76d5f1991584 (at node_modules/.pnpm/@prisma+engines@5.0.0/node_modules/@prisma/engines/schema-engine-darwin-arm64)
Schema Wasm             : @prisma/prisma-schema-wasm 4.17.0-26.6b0aef69b7cdfc787f822ecd7cdc76d5f1991584
Default Engines Hash    : 6b0aef69b7cdfc787f822ecd7cdc76d5f1991584
Studio                  : 0.487.0

[Jolg42]

@p-kuen and upvoters: The fix is merged and will be a part of 5.1 release.
You can try 5.1.0-dev.28 development snapshot and let us know if that version works for you. We don't recommend using it in production, but it should be enough to confirm the fix.

[p-kuen]

Thanks for the fix! We will test the dev version. The PR shows a negative impact in typescript compilation, do I read this correctly? But I think it's still better than in versions before 5.0.0, right?

[Jolg42]

@p-kuen I guess you saw the "Codspeed" comment #20197 (comment) It is unfortunately not reliable for this, so it's hard to say if there is any actual performance impact.
I definitely recommend ignoring it and using 5.0.0 and up.

[p-kuen]

I can confirm that the Fluent API error is fixed with current dev version (5.1.0-dev.61), although I have lots of other errors with enums and other typings. We will wait until the release of 5.1.0 and look if problems still exist.
Thanks again for the fix!