findMany broken with many relations to same entity

Bug description

When making a findMany query to an entity (A) that has a ManyToMany relation to another entity (B), if B is referred to in many of the returned A entities, only one of the A entities actually has B returned.

How to reproduce

1. Run a findMany query with a Many to Many relationship
2. Have many of the base entities reference the same related entity
3. Only one of the base entities will have the related entity in the response

Expected behavior

All related entities should be returned correctly in the prisma mapping.

Prisma information

Schema

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

generator client {
  provider = "prisma-client-js"
  output   = "../node_modules/@prisma/client/generated"
}

model Group {
  groupId   BigInt   @id
  users     User[]
  tags      Tag[]
  broadcasts Boolean @default(true)
  adminOnly Boolean @default(false)
  createdAt DateTime @default(now())
  updatedAt DateTime @updatedAt
}

model User {
  userId     BigInt     @id
  groups     Group[]
  tags       Tag[]
  username   String?
  firstName  String?
  lastName   String?
  lastSeen   DateTime   @default(now())
  createdAt  DateTime   @default(now())
  updatedAt  DateTime   @updatedAt
}

model Tag {
  tagId      String     @id @default(uuid())
  name       String
  group      Group      @relation(fields: [groupId], references: [groupId])
  groupId    BigInt
  users      User[]
  lastUsed   DateTime?
  createdAt  DateTime   @default(now())
  updatedAt  DateTime   @updatedAt

  @@unique([name, groupId])
}

Query

const tags = await prisma.tag.findMany({
  where: { groupId },
  include: { users: true }
});

Environment & setup

• OS: Windows and Linux
• Database: PostgreSQL
• Node.js version: v14.17.5

Prisma Version

$ prisma -v                                                       
Environment variables loaded from .env
prisma                  : 3.10.0
@prisma/client          : 3.10.0
Current platform        : windows
Query Engine (Node-API) : libquery-engine 73e60b76d394f8d37d8ebd1f8918c79029f0db86 (at node_modules\@prisma\e
ngines\query_engine-windows.dll.node)
Migration Engine        : migration-engine-cli 73e60b76d394f8d37d8ebd1f8918c79029f0db86 (at node_modules\@pri
sma\engines\migration-engine-windows.exe)
Introspection Engine    : introspection-core 73e60b76d394f8d37d8ebd1f8918c79029f0db86 (at node_modules\@prism
a\engines\introspection-engine-windows.exe)
Format Binary           : prisma-fmt 73e60b76d394f8d37d8ebd1f8918c79029f0db86 (at node_modules\@prisma\engine
s\prisma-fmt-windows.exe)
Default Engines Hash    : 73e60b76d394f8d37d8ebd1f8918c79029f0db86
Studio                  : 0.458.0

Example:

This query:

const tag = await prisma.tag.findUnique({
  select: { users: true, name: true },
  where: { name_groupId: { groupId, name } },
  rejectOnNotFound: false
});

returns the following for the respective args:

(groupid: A, name: 'test')
{
  users: [
    {
      userId: 87425504n,
      username: 'zackpollard',
      firstName: 'Zack',
      lastName: 'Pollard',
      lastSeen: 2022-03-09T00:43:48.688Z,
      createdAt: 2022-02-28T02:42:03.063Z,
      updatedAt: 2022-03-09T00:43:48.721Z
    }
  ],
  name: 'test'
}

(groupId: A, name: 'test2')
{
  users: [
    {
      userId: 87425504n,
      username: 'zackpollard',
      firstName: 'Zack',
      lastName: 'Pollard',
      lastSeen: 2022-03-09T00:44:49.338Z,
      createdAt: 2022-02-28T02:42:03.063Z,
      updatedAt: 2022-03-09T00:44:49.340Z
    }
  ],
  name: 'test2'
}

The findMany query for the same group:

const tags = await prisma.tag.findMany({
  where: { groupId },
  include: { users: true }
});

Returns:

(groupId: A)
[
  {
    tagId: 'b573fab0-1043-480c-a1c1-51edd1eff4c3',
    name: 'test',
    groupId: -747796799n,
    createdAt: 2022-02-28T02:42:03.296Z,
    updatedAt: 2022-02-28T02:42:03.296Z,
    users: []
  },
  {
    tagId: 'f2357c37-a468-461a-bc15-d05f010eb787',
    name: 'test2',
    groupId: -747796799n,
    lastUsed: null,
    createdAt: 2022-03-09T00:20:00.584Z,
    updatedAt: 2022-03-09T00:20:00.585Z,
    users: [ [Object] ]
  }
]

As you can see, the first tag “test” is missing the user that “test2” shares with it

[zackpollard]

Hey folks,

Either I’m doing something wrong or there’s something going on with your data. Either way, I unfortunately can’t reproduce your issue.

Would you mind setting up a small reproduction with seed data?

Thank you 🙏

Hey Weakky,

It’s been a while since i’ve worked on this code. However the issue exists when two entities (tags) return a nested array of entities (users) that share one of the related entities, i.e. both have the same user connected to the tag. In that case, only one of the tags shows the user whereas both should show it. In your data set if you add Flavian to tag_b or Zack to tag_a you should see the problem.

Cheers!

[zackpollard]

Excellent, thankyou for resolving it @Weakky