# Expand-and-contract migrations

## [Introduction](#introduction)

When you change your database schema in production, you need to keep the data consistent and avoid downtime. This guide shows you how to use the expand and contract pattern to safely migrate data between columns. The example replaces a boolean field with an enum field while preserving existing data.

## [Prerequisites](#prerequisites)

Before starting this guide, make sure you have:

- Node.js installed (version 20 or higher)
- A Prisma ORM project with an existing schema
- A supported database (PostgreSQL, MySQL, SQLite, SQL Server, etc.)
- Access to both development and production databases
- Basic understanding of Git branching
- Basic familiarity with TypeScript

## [1. Set up your environment](#1-set-up-your-environment)

### [1.1. Review initial schema](#11-review-initial-schema)

Start with a basic schema containing a Post model:

```
generator client {

  provider = "prisma-client"

  output   = "./generated/prisma"

}

datasource db {

  provider = "postgresql"

}

model Post {

  id        Int     @id @default(autoincrement())

  title     String

  content   String?

  published Boolean @default(false)

}
```

### [1.2. Configure Prisma](#12-configure-prisma)

Create a `prisma.config.ts` file in the root of your project with the following content:

```title="prisma.config.ts"
import "dotenv/config";

import { defineConfig, env } from "prisma/config";

export default defineConfig({

  schema: "prisma/schema.prisma",

  migrations: {

    path: "prisma/migrations",

  },

  datasource: {

    url: env("DATABASE_URL"),

  },

});
```

:::::callout{intent="note"}
You'll need to install the required packages. If you haven't already, install them using your package manager:

::::tabs
:::tab{title="bun"}
```
bun add prisma@prev tsx @types/pg --dev
```
:::

:::tab{title="pnpm"}
```bash
pnpm prisma migrate dev --name add-status-column
```
:::

:::tab{title="yarn"}
```bash
yarn prisma migrate dev --name add-status-column
```
:::

:::tab{title="npm"}
```bash
npx prisma migrate dev --name add-status-column
```

Then generate Prisma Client:
:::
::::

:::code-group
```title="bun"
bun add @prisma/client@7 @prisma/adapter-pg pg dotenv
```

```bash title="pnpm"
pnpm prisma generate
```

```bash title="yarn"
yarn prisma generate
```

```bash title="npm"
npx prisma generate
```
:::

If you are using a different database provider (MySQL, SQL Server, SQLite), install the corresponding driver adapter package instead of `@prisma/adapter-pg`. For more information, see [Database drivers](/guides/core-concepts-v7-supported-databases-database-drivers).
:::::

### [1.3. Create a development branch](#13-create-a-development-branch)

Create a new branch for your changes:

```
git checkout -b create-status-field
```

## [2. Expand the schema](#2-expand-the-schema)

### [2.1. Add new column](#21-add-new-column)

Update your schema to add the new Status enum and field:

```
model Post {

  id        Int      @id @default(autoincrement())

  title     String

  content   String?

  published Boolean? @default(false)

  status    Status   @default(Unknown)

}

enum Status {

  Unknown

  Draft

  InProgress

  InReview

  Published

}
```

### [2.2. Create migration](#22-create-migration)

Generate the migration:

:::code-group
```title="bun"
bunx prisma migrate dev --name add-status-column
```

```bash title="pnpm"
pnpm run data-migration:add-status-column
```

```bash title="yarn"
yarn data-migration:add-status-column
```

```bash title="npm"
npm run data-migration:add-status-column
```
:::

Then generate Prisma Client:

::::tabs
:::tab{title="bun"}
```
bunx prisma generate
```
:::

:::tab{title="pnpm"}
```bash
pnpm prisma migrate dev --name drop-published-column
```
:::

:::tab{title="yarn"}
```bash
yarn prisma migrate dev --name drop-published-column
```
:::

:::tab{title="npm"}
```bash
npx prisma migrate dev --name drop-published-column
```

Then generate Prisma Client:
:::
::::

## [3. Migrate the data](#3-migrate-the-data)

### [3.1. Create migration script](#31-create-migration-script)

Create a new TypeScript file for the data migration:

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

import { PrismaPg } from "@prisma/adapter-pg";

import "dotenv/config";

const adapter = new PrismaPg({

  connectionString: process.env.DATABASE_URL,

});

const prisma = new PrismaClient({

  adapter,

});

async function main() {

  await prisma.$transaction(async (tx) => {

    const posts = await tx.post.findMany();

    for (const post of posts) {

      await tx.post.update({

        where: { id: post.id },

        data: {

          status: post.published ? "Published" : "Unknown",

        },

      });

    }

  });

}

main()

  .catch(async (e) => {

    console.error(e);

    process.exit(1);

  })

  .finally(async () => await prisma.$disconnect());
```

### [3.2. Set up migration script](#32-set-up-migration-script)

Add the migration script to your package.json:

```
{

  "scripts": {

    "data-migration:add-status-column": "tsx ./prisma/migrations/<migration-timestamp>/data-migration.ts"

  }

}
```

### [3.3. Execute migration](#33-execute-migration)

1. Update your DATABASE\_URL to point to the production database
2. Run the migration script:

:::code-group
```title="bun"
bun run data-migration:add-status-column
```

```bash title="pnpm"
pnpm prisma generate
```

```bash title="yarn"
yarn prisma generate
```

```bash title="npm"
npx prisma generate
```
:::

## [4. Contract the schema](#4-contract-the-schema)

### [4.1. Create cleanup branch](#41-create-cleanup-branch)

Create a new branch for removing the old column:

```
git checkout -b drop-published-column
```

### [4.2. Remove old column](#42-remove-old-column)

Update your schema to remove the published field:

```
model Post {

  id      Int      @id @default(autoincrement())

  title   String

  content String?

  status  Status   @default(Draft)

}

enum Status {

  Draft

  InProgress

  InReview

  Published

}
```

### [4.3. Generate cleanup migration](#43-generate-cleanup-migration)

Create and run the final migration:

:::code-group
```title="bun"
bunx prisma migrate dev --name drop-published-column
```

```bash title="pnpm"
pnpm prisma migrate deploy
```

```bash title="yarn"
yarn prisma migrate deploy
```

```bash title="npm"
npx prisma migrate deploy
```
:::

Then generate Prisma Client:

::::tabs
:::tab{title="bun"}
```
bunx prisma generate
```
:::

:::tab{title="pnpm"}
:::

:::tab{title="yarn"}
:::

:::tab{title="npm"}
:::
::::

## [5. Deploy to production](#5-deploy-to-production)

### [5.1. Set up deployment](#51-set-up-deployment)

Add the following command to your CI/CD pipeline:

::::tabs
:::tab{title="bun"}
```
bunx prisma migrate deploy
```
:::

:::tab{title="pnpm"}
:::

:::tab{title="yarn"}
:::

:::tab{title="npm"}
:::
::::

### [5.2. Monitor deployment](#52-monitor-deployment)

Watch for any errors in your logs and monitor your application's behavior after deployment.

## [Troubleshooting](#troubleshooting)

### [Common issues and solutions](#common-issues-and-solutions)

1. **Migration fails due to missing default**

   - Ensure you've added a proper default value
   - Check that all existing records can be migrated

2. **Data loss prevention**

   - Always backup your database before running migrations
   - Test migrations on a copy of production data first

3. **Transaction rollback**

   - If the data migration fails, the transaction will automatically rollback
   - Fix any errors and retry the migration

## [Next steps](#next-steps)

Now that you've completed your first expand and contract migration, you can:

- Learn more about [Prisma Migrate](/guides/prisma-migrate-v7-prisma-migrate)
- Explore [schema prototyping](/guides/prisma-migrate-v7-workflows-prototyping-your-schema)
- Understand [customizing migrations](/guides/prisma-migrate-v7-workflows-customizing-migrations)

For more information:

- [Expand and Contract Pattern Documentation](https://www.prisma.io/dataguide/types/relational/expand-and-contract-pattern)
- [Prisma Migrate Workflows](/guides/prisma-migrate-v7-workflows-development-and-production)

## 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)
- [Database](./database-index.md)
- [DB commands](./db-commands-index.md)

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