relationJoins MySQL converts nested Decimal to float

[michaelhays]

Bug description

When using relationLoadStrategy: 'join' in MySQL, retrieving nested models with Decimal fields seem to convert decimal values to floats.

How to reproduce

https://github.com/michaelhays/prisma-relationjoins-decimal

See these lines for what gets logged.

console.log(queryResult) // 95993.57
console.log(joinResult) // 95993.57000000001

Prisma information

generator client {
  provider        = "prisma-client-js"
  previewFeatures = ["relationJoins"]
}

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

model FirstModel {
  id           Int           @id @default(autoincrement())
  secondModels SecondModel[]
}

model SecondModel {
  id           Int        @id @default(autoincrement())
  value        Decimal
  firstModelId Int
  firstModel   FirstModel @relation(fields: [firstModelId], references: [id])

  @@index([firstModelId])
}

const joinResult = (await prisma.firstModel.findFirstOrThrow({
  relationLoadStrategy: 'join',
  include: { secondModels: true },
})).secondModels[0].value

Environment & setup

• OS: Linux, Fedora 39
• Database: MySQL
• Node.js version: v20.11.0

Prisma Version

prisma                  : 5.10.2
@prisma/client          : 5.10.2
Computed binaryTarget   : rhel-openssl-3.0.x
Operating System        : linux
Architecture            : x64
Node.js                 : v20.11.0
Query Engine (Node-API) : libquery-engine 5a9203d0590c951969e85a7d07215503f4672eb9 (at node_modules/@prisma/engines/libquery_engine-rhel-openssl-3.0.x.so.node)
Schema Engine           : schema-engine-cli 5a9203d0590c951969e85a7d07215503f4672eb9 (at node_modules/@prisma/engines/schema-engine-rhel-openssl-3.0.x)
Schema Wasm             : @prisma/prisma-schema-wasm 5.10.0-34.5a9203d0590c951969e85a7d07215503f4672eb9
Default Engines Hash    : 5a9203d0590c951969e85a7d07215503f4672eb9
Studio                  : 0.499.0
Preview Features        : relationJoins

[planklmar]

We found the same issue using Postgres, when using relationLoadStrategy: 'join'.
With load strategy relationLoadStrategy: 'query' or deactivating the preview Feature, the values are correct again.

In the query using "relationJoins", I can see a JSONB_BUILD_OBJECT maybe this is causing a wrong conversion to number at some point

Should I open another issue or can I leave this here?

prisma : 5.10.2
@prisma/client : 5.10.2
Postgres : 12
PreviewFeature: "relationJoins"

[Weakky]

Hey folks, this issue should be fixed in the next release of Prisma. Thanks for reporting 🙏

[michaelhays]

Confirmed that this is fixed in 5.12.0! Thanks so much y'all :)