Database Migration

# database-migration — additional patterns and templates

## Zero-Downtime Migrations

### Blue-Green Deployment Strategy

```javascript
// Phase 1: Make changes backward compatible
module.exports = {
  up: async (queryInterface, Sequelize) => {
    // Add new column (both old and new code can work)
    await queryInterface.addColumn("users", "email_new", {
      type: Sequelize.STRING,
    });
  },
};

// Phase 2: Deploy code that writes to both columns

// Phase 3: Backfill data
module.exports = {
  up: async (queryInterface) => {
    await queryInterface.sequelize.query(`
      UPDATE users
      SET email_new = email
      WHERE email_new IS NULL
    `);
  },
};

// Phase 4: Deploy code that reads from new column

// Phase 5: Remove old column
module.exports = {
  up: async (queryInterface) => {
    await queryInterface.removeColumn("users", "email");
  },
};
```

## Cross-Database Migrations

### PostgreSQL to MySQL

```javascript
// Handle differences
module.exports = {
  up: async (queryInterface, Sequelize) => {
    const dialectName = queryInterface.sequelize.getDialect();

    if (dialectName === "mysql") {
      await queryInterface.createTable("users", {
        id: {
          type: Sequelize.INTEGER,
          primaryKey: true,
          autoIncrement: true,
        },
        data: {
          type: Sequelize.JSON, // MySQL JSON type
        },
      });
    } else if (dialectName === "postgres") {
      await queryInterface.createTable("users", {
        id: {
          type: Sequelize.INTEGER,
          primaryKey: true,
          autoIncrement: true,
        },
        data: {
          type: Sequelize.JSONB, // PostgreSQL JSONB type
        },
      });
    }
  },
};
```


---
name: database-migration
description: Execute database migrations across ORMs and platforms with zero-downtime strategies, data transformation, and rollback procedures. Use when migrating databases, changing schemas, performing data transformations, or implementing zero-downtime deployment strategies.
---

# Database Migration

Master database schema and data migrations across ORMs (Sequelize, TypeORM, Prisma), including rollback strategies and zero-downtime deployments.

## When to Use This Skill

- Migrating between different ORMs
- Performing schema transformations
- Moving data between databases
- Implementing rollback procedures
- Zero-downtime deployments
- Database version upgrades
- Data model refactoring

## ORM Migrations

### Sequelize Migrations

```javascript
// migrations/20231201-create-users.js
module.exports = {
  up: async (queryInterface, Sequelize) => {
    await queryInterface.createTable("users", {
      id: {
        type: Sequelize.INTEGER,
        primaryKey: true,
        autoIncrement: true,
      },
      email: {
        type: Sequelize.STRING,
        unique: true,
        allowNull: false,
      },
      createdAt: Sequelize.DATE,
      updatedAt: Sequelize.DATE,
    });
  },

  down: async (queryInterface, Sequelize) => {
    await queryInterface.dropTable("users");
  },
};

// Run: npx sequelize-cli db:migrate
// Rollback: npx sequelize-cli db:migrate:undo
```

### TypeORM Migrations

```typescript
// migrations/1701234567-CreateUsers.ts
import { MigrationInterface, QueryRunner, Table } from "typeorm";

export class CreateUsers1701234567 implements MigrationInterface {
  public async up(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.createTable(
      new Table({
        name: "users",
        columns: [
          {
            name: "id",
            type: "int",
            isPrimary: true,
            isGenerated: true,
            generationStrategy: "increment",
          },
          {
            name: "email",
            type: "varchar",
            isUnique: true,
          },
          {
            name: "created_at",
            type: "timestamp",
            default: "CURRENT_TIMESTAMP",
          },
        ],
      }),
    );
  }

  public async down(queryRunner: QueryR