Bug description

Count relations does not work with the new queryCompiler feature enabled.

This does not affect the db.user.count() which works as expected.

Severity

🚨 Critical: Data loss, app crash, security issue

Reproduction

https://github.com/hrougier/prisma-query-compiler-count-issue

Expected vs. Actual Behavior

I expect the _count property to have a value.

Frequency

Consistently reproducible

Does this occur in development or production?

Both development and production

Is this a regression?

No, it's still a preview feature

Workaround

Remove the queryCompiler feature flag, run prisma generate again and now it works:

[
  {
    "id": 1,
    "name": "Alice",
    "_count": {
      "posts": 2
    }
  },
  {
    "id": 2,
    "name": "Bob",
    "_count": {
      "posts": 1
    }
  }
]

Prisma Schema & Queries

Using the queryCompiler preview feature in schema.prisma

generator client {
  provider        = "prisma-client"
  output          = "./generated"
  moduleFormat    = "esm"
  previewFeatures = ["driverAdapters", "queryCompiler"]
}

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
}

model User {
  id    Int     @id @default(autoincrement())
  email String  @unique
  name  String?
  posts Post[]
}

model Post {
  id        Int     @id @default(autoincrement())
  title     String
  content   String?
  published Boolean @default(false)
  authorId  Int
  author    User    @relation(fields: [authorId], references: [id])
}

and counting relations between User and Post:

await prisma.user.findMany({
    select: {
      id: true,
      name: true,
      _count: {
        select: {
          posts: true,
        },
      },
    }

    // same issue using:

    // include: {
    //   _count: {
    //     select: { posts: true },
    //   },
    // },
  })

returns nothing for the _count property:

[
  {
    "id": 1,
    "name": "Alice"
  },
  {
    "id": 2,
    "name": "Bob"
  }
]

Prisma Config

// Add your `prisma.config.ts`

Logs & Debug Info

// Debug logs here

Environment & Setup

• OS: macOS
• Database: PostgreSQL
• Node.js version: v22.15.0

Prisma Version

prisma                  : 6.7.0
@prisma/client          : 6.7.0
Computed binaryTarget   : darwin-arm64
Operating System        : darwin
Architecture            : arm64
Node.js                 : v22.15.0
TypeScript              : 5.8.3
Query Engine (Node-API) : libquery-engine 3cff47a7f5d65c3ea74883f1d736e41d68ce91ed (at node_modules/@prisma/engines/libquery_engine-darwin-arm64.dylib.node)
Schema Engine           : schema-engine-cli 3cff47a7f5d65c3ea74883f1d736e41d68ce91ed (at node_modules/@prisma/engines/schema-engine-darwin-arm64)
Schema Wasm             : @prisma/prisma-schema-wasm 6.7.0-36.3cff47a7f5d65c3ea74883f1d736e41d68ce91ed
Default Engines Hash    : 3cff47a7f5d65c3ea74883f1d736e41d68ce91ed
Studio                  : 0.511.0
Preview Features        : driverAdapters, queryCompiler