# Many-to-many relations (Prisma ORM v7) (/docs/orm/v7/more/troubleshooting/many-to-many-relations)

Learn how to model, query, and convert many-to-many relations with Prisma ORM

Location: ORM > v7 > More > Troubleshooting > Many-to-many relations

Modeling and querying many-to-many relations in relational databases can be challenging. This guide shows how to work with [implicit](/guides/prisma-schema-v7-data-model-relations-many-to-many-relations#implicit-many-to-many-relations) and [explicit](/guides/prisma-schema-v7-data-model-relations-many-to-many-relations#explicit-many-to-many-relations) many-to-many relations, and how to convert between them.

## Implicit relations

Implicit many-to-many relations let Prisma ORM handle the [relation table](/guides/prisma-schema-v7-data-model-relations-many-to-many-relations#relation-table-conventions) internally:

```prisma
model Post {
  id    Int    @id @default(autoincrement())
  title String
  tags  Tag[]
}

model Tag {
  id    Int    @id @default(autoincrement())
  name  String @unique
  posts Post[]
}
```

### Creating records

```ts
await prisma.post.create({
  data: {
    title: "Types of relations",
    tags: { create: [{ name: "dev" }, { name: "prisma" }] },
  },
});
```

### Querying with relations

```ts
await prisma.post.findMany({
  include: { tags: true },
});
```

Result:

```json
[
  {
    "id": 1,
    "title": "Types of relations",
    "tags": [
      { "id": 1, "name": "dev" },
      { "id": 2, "name": "prisma" }
    ]
  }
]
```

### Connecting and creating tags simultaneously

```ts
await prisma.post.update({
  where: { id: 1 },
  data: {
    title: "Prisma is awesome!",
    tags: { set: [{ id: 1 }, { id: 2 }], create: { name: "typescript" } },
  },
});
```

## Explicit relations

Explicit relations are needed when you need to store extra fields in the relation table or when [introspecting](/guides/prisma-schema-v7-introspection) an existing database:

```prisma
model Post {
  id    Int        @id @default(autoincrement())
  title String
  tags  PostTags[]
}

model PostTags {
  id     Int   @id @default(autoincrement())
  post   Post? @relation(fields: [postId], references: [id])
  tag    Tag?  @relation(fields: [tagId], references: [id])
  postId Int?
  tagId  Int?

  @@index([postId, tagId])
}

model Tag {
  id    Int        @id @default(autoincrement())
  name  String     @unique
  posts PostTags[]
}
```

### Creating records with explicit relations

```ts
await prisma.post.create({
  data: {
    title: "Types of relations",
    tags: {
      create: [{ tag: { create: { name: "dev" } } }, { tag: { create: { name: "prisma" } } }],
    },
  },
});
```

### Querying with explicit relations

```ts
await prisma.post.findMany({
  include: { tags: { include: { tag: true } } },
});
```

### Mapping the response

To get a cleaner response similar to implicit relations:

```ts
const result = posts.map((post) => {
  return { ...post, tags: post.tags.map((tag) => tag.tag) };
});
```

## Converting implicit to explicit relations

Sometimes you need to transition from implicit to explicit relations, for example to add metadata like timestamps to the relation.

### Step 1: Add the explicit relation model

Keep the implicit relation while adding the new model:

```prisma
model User {
  id        Int        @id @default(autoincrement())
  name      String
  posts     Post[]
  userPosts UserPost[]
}

model Post {
  id        Int        @id @default(autoincrement())
  title     String
  authors   User[]
  userPosts UserPost[]
}

model UserPost {
  id        Int       @id @default(autoincrement())
  userId    Int
  postId    Int
  user      User      @relation(fields: [userId], references: [id])
  post      Post      @relation(fields: [postId], references: [id])
  createdAt DateTime  @default(now())

  @@unique([userId, postId])
}
```

Run the migration:

#### bun

```bash
bunx prisma migrate dev --name "added explicit relation"
```

#### pnpm

```bash
pnpm prisma migrate dev --name "added explicit relation"
```

#### yarn

```bash
yarn prisma migrate dev --name "added explicit relation"
```

#### npm

```bash
npx prisma migrate dev --name "added explicit relation"
```

### Step 2: Migrate existing data

```typescript
import { PrismaClient } from "../prisma/generated/client";

const prisma = new PrismaClient();

async function main() {
  const users = await prisma.user.findMany({
    include: { posts: true },
  });

  for (const user of users) {
    for (const post of user.posts) {
      await prisma.userPost.create({
        data: {
          userId: user.id,
          postId: post.id,
        },
      });
    }
  }

  console.log("Data migration completed.");
}

main()
  .catch((e) => {
    throw e;
  })
  .finally(async () => {
    await prisma.$disconnect();
  });
```

### Step 3: Remove implicit relation columns

After migrating the data, remove the implicit relation columns:

```prisma
model User {
  id        Int        @id @default(autoincrement())
  name      String
  userPosts UserPost[]
}

model Post {
  id        Int        @id @default(autoincrement())
  title     String
  userPosts UserPost[]
}
```

Run the migration:

#### bun

```bash
bunx prisma migrate dev --name "removed implicit relation"
```

#### pnpm

```bash
pnpm prisma migrate dev --name "removed implicit relation"
```

#### yarn

```bash
yarn prisma migrate dev --name "removed implicit relation"
```

#### npm

```bash
npx prisma migrate dev --name "removed implicit relation"
```

This will drop the implicit table `_PostToUser`.

## Related pages

- [`Bundler issues`](/guides/more-4-v7-more-troubleshooting-bundler-issues): Solve ENOENT package error with vercel/pkg and other bundlers
- [`Check constraints`](/guides/more-4-v7-more-troubleshooting-check-constraints): Learn how to configure CHECK constraints for data validation with Prisma ORM and PostgreSQL
- [`GraphQL autocompletion`](/guides/more-4-v7-more-troubleshooting-graphql-autocompletion): Get autocompletion for Prisma Client queries in GraphQL resolvers with plain JavaScript
- [`Next.js`](/guides/more-4-v7-more-troubleshooting-nextjs): Best practices and troubleshooting for using Prisma ORM with Next.js applications
- [`Nuxt`](/guides/more-4-v7-more-troubleshooting-nuxt): Learn how to integrate Prisma ORM with your Nuxt application

## Related pages

- [Authentication & Tools](./authentication-tools-index.md)
- [Build](./build-index.md)
- [Changelog](../changelog.md)
- [Concepts](./concepts-index.md)
- [Console commands](./console-commands-index.md)
- [Contract Authoring](./contract-authoring-index.md)
- [Core Concepts](./core-concepts-index.md)
- [Data Modeling](./data-modeling-index.md)
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- [DB commands](./db-commands-index.md)

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