Prisma 6.9.0 error [DataMapperError]: Missing data field on query with @map("snake_case") attribute

[anonnoisy]

Bug description

When querying a model that uses the @map attribute to map a snake_case database column to a camelCase model field, Prisma's data mapper incorrectly fails to find the field in the result set.

The generated SQL query correctly uses an alias (e.g., SELECT "column_name" AS "columnName"). The data returned from the database driver also correctly contains the aliased camelCase key. However, the final data mapping layer still seems to search for the original snake_case key, causing a DataMapperError: Missing data field error.

Severity

🚨 Critical: Data loss, app crash, security issue

Reproduction

How to Reproduce

1. Define the following generic schema in prisma/schema.prisma:

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

generator client {
  provider = "prisma-client-js"
}

model BlogPost {
  id          Int       @id @default(autoincrement())
  title       String    @unique
  publishedAt DateTime? @map("published_at")

  @@map("blog_posts")
}

2. Run prisma db push to sync the schema with the database.

3. Run the following TypeScript code to query the data:

import { PrismaClient } from '@prisma/client';
import { PrismaPg } from '@prisma/adapter-pg'

const adapter = new PrismaPg({ connectionString: process.env.DATABASE_URL })
const prisma = new PrismaClient({ adapter })

async function main() {
  // Seed some data first
  const postTitle = 'Hello World';
  await prisma.blogPost.create({
    data: {
      title: postTitle,
      publishedAt: new Date(),
    },
  });

  // This is the query that fails
  try {
    const post = await prisma.blogPost.findUnique({
      where: {
        title: postTitle,
      },
    });
    console.log('Found post:', post);
  } catch (error) {
    console.error('An error occurred:', error);
  } finally {
    await prisma.$disconnect();
  }
}

main();

4. Observe the error in the console.

Expected vs. Actual Behavior

Expected behavior The query should successfully execute and return the BlogPost object. The program should log something similar to: Found post: { id: 1, title: 'Hello World', publishedAt: 2025-06-16T08:38:00.000Z }

Actual behavior The query fails with a DataMapperError. The logs would show the following pattern (adapted for this new example):

prisma:query SELECT "t0"."id", "t0"."title", "t0"."published_at" AS "publishedAt" FROM "public"."blog_posts" AS "t0" WHERE "t0"."title" = $1 LIMIT $2
prisma:error Missing data field (Value): 'published_at'; node: {"type":"Value","dbName":"published_at","resultType":{"type":"DateTime"}}; data: {"id":1, "title": "Hello World", "publishedAt":"2025-06-16T08:38:00.000+00:00"}
prisma:query ROLLBACK
An error occurred: [DataMapperError]: Missing data field (Value): 'published_at'; node: {"type":"Value","dbName":"published_at","resultType":{"type":"DateTime"}}; data: {"id":1, "title": "Hello World", "publishedAt":"2025-06-16T08:38:00.000+00:00"}

Frequency

Consistently reproducible

Does this occur in development or production?

Both development and production

Is this a regression?

Yes, last worked in Prisma 6.6.0, broke in 6.9.0

Workaround

Revert upgrade to 6.6.0

Prisma Schema & Queries

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

generator client {
  provider = "prisma-client-js"
}

model BlogPost {
  id          Int       @id @default(autoincrement())
  title       String    @unique
  publishedAt DateTime? @map("published_at")

  @@map("blog_posts")
}

import { PrismaClient } from '@prisma/client';
import { PrismaPg } from '@prisma/adapter-pg'

const adapter = new PrismaPg({ connectionString: process.env.DATABASE_URL })
const prisma = new PrismaClient({ adapter })

async function main() {
  // Seed some data first
  const postTitle = 'Hello World';
  await prisma.blogPost.create({
    data: {
      title: postTitle,
      publishedAt: new Date(),
    },
  });

  // This is the query that fails
  try {
    const post = await prisma.blogPost.findUnique({
      where: {
        title: postTitle,
      },
    });
    console.log('Found post:', post);
  } catch (error) {
    console.error('An error occurred:', error);
  } finally {
    await prisma.$disconnect();
  }
}

main();

Prisma Config

No response

Logs & Debug Info

prisma:query SELECT "t0"."id", "t0"."title", "t0"."published_at" AS "publishedAt" FROM "public"."blog_posts" AS "t0" WHERE "t0"."title" = $1 LIMIT $2
prisma:error Missing data field (Value): 'published_at'; node: {"type":"Value","dbName":"published_at","resultType":{"type":"DateTime"}}; data: {"id":1, "title": "Hello World", "publishedAt":"2025-06-16T08:38:00.000+00:00"}
prisma:query ROLLBACK
An error occurred: [DataMapperError]: Missing data field (Value): 'published_at'; node: {"type":"Value","dbName":"published_at","resultType":{"type":"DateTime"}}; data: {"id":1, "title": "Hello World", "publishedAt":"2025-06-16T08:38:00.000+00:00"}

Environment & Setup

• OS: macOs
• Database: PostgreSQL
• Node.js version: v20.12.2

Prisma Version

Environment variables loaded from .env
Prisma schema loaded from src/infrastructures/database/prisma/schema
prisma                  : 6.9.0
@prisma/client          : 6.9.0
Computed binaryTarget   : darwin
Operating System        : darwin
Architecture            : x64
Node.js                 : v20.12.2
TypeScript              : 5.8.3
Query Engine (Node-API) : libquery-engine 81e4af48011447c3cc503a190e86995b66d2a28e (at node_modules/.pnpm/@[email protected]/node_modules/@prisma/engines/libquery_engine-darwin.dylib.node)
Schema Engine           : schema-engine-cli 81e4af48011447c3cc503a190e86995b66d2a28e (at node_modules/.pnpm/@[email protected]/node_modules/@prisma/engines/schema-engine-darwin)
Schema Wasm             : @prisma/prisma-schema-wasm 6.9.0-10.81e4af48011447c3cc503a190e86995b66d2a28e
Default Engines Hash    : 81e4af48011447c3cc503a190e86995b66d2a28e
Studio                  : 0.511.0