database-migration

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

// 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

// 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: QueryRunner): Promise<void> { await queryRunner.dropTable('users'); } }

// Run: npm run typeorm migration:run // Rollback: npm run typeorm migration:revert

Prisma Migrations

// schema.prisma model User { id Int @id @default(autoincrement()) email String @unique createdAt DateTime @default(now()) }

// Generate migration: npx prisma migrate dev --name create_users // Apply: npx prisma migrate deploy

Schema Transformations

Adding Columns with Defaults

// Safe migration: add column with default module.exports = { up: async (queryInterface, Sequelize) => { await queryInterface.addColumn('users', 'status', { type: Sequelize.STRING, defaultValue: 'active', allowNull: false }); },

down: async (queryInterface) => { await queryInterface.removeColumn('users', 'status'); } };

Renaming Columns (Zero Downtime)

// Step 1: Add new column module.exports = { up: async (queryInterface, Sequelize) => { await queryInterface.addColumn('users', 'full_name', { type: Sequelize.STRING });

// Copy data from old column
await queryInterface.sequelize.query(
  'UPDATE users SET full_name = name'
);

down: async (queryInterface) => { await queryInterface.removeColumn('users', 'full_name'); } };

// Step 2: Update application to use new column

// Step 3: Remove old column module.exports = { up: async (queryInterface) => { await queryInterface.removeColumn('users', 'name'); },

down: async (queryInterface, Sequelize) => { await queryInterface.addColumn('users', 'name', { type: Sequelize.STRING }); } };

Changing Column Types

module.exports = { up: async (queryInterface, Sequelize) => { // For large tables, use multi-step approach

// 1. Add new column
await queryInterface.addColumn('users', 'age_new', {
  type: Sequelize.INTEGER
});

// 2. Copy and transform data
await queryInterface.sequelize.query(`
  UPDATE users
  SET age_new = CAST(age AS INTEGER)
  WHERE age IS NOT NULL
`);

// 3. Drop old column
await queryInterface.removeColumn('users', 'age');

// 4. Rename new column
await queryInterface.renameColumn('users', 'age_new', 'age');

down: async (queryInterface, Sequelize) => { await queryInterface.changeColumn('users', 'age', { type: Sequelize.STRING }); } };

Data Transformations

Complex Data Migration

module.exports = { up: async (queryInterface, Sequelize) => { // Get all records const [users] = await queryInterface.sequelize.query( 'SELECT id, address_string FROM users' );

// Transform each record
for (const user of users) {
  const addressParts = user.address_string.split(',');

  await queryInterface.sequelize.query(
    `UPDATE users
     SET street = :street,
         city = :city,
         state = :state
     WHERE id = :id`,
    {
      replacements: {
        id: user.id,
        street: addressParts[0]?.trim(),
        city: addressParts[1]?.trim(),
        state: addressParts[2]?.trim()
      }
    }
  );
}

// Drop old column
await queryInterface.removeColumn('users', 'address_string');

down: async (queryInterface, Sequelize) => { // Reconstruct original column await queryInterface.addColumn('users', 'address_string', { type: Sequelize.STRING });

await queryInterface.sequelize.query(`
  UPDATE users
  SET address_string = CONCAT(street, ', ', city, ', ', state)
`);

await queryInterface.removeColumn('users', 'street');
await queryInterface.removeColumn('users', 'city');
await queryInterface.removeColumn('users', 'state');

} };

Rollback Strategies

Transaction-Based Migrations

module.exports = { up: async (queryInterface, Sequelize) => { const transaction = await queryInterface.sequelize.transaction();

try {
  await queryInterface.addColumn(
    'users',
    'verified',
    { type: Sequelize.BOOLEAN, defaultValue: false },
    { transaction }
  );

  await queryInterface.sequelize.query(
    'UPDATE users SET verified = true WHERE email_verified_at IS NOT NULL',
    { transaction }
  );

  await transaction.commit();
} catch (error) {
  await transaction.rollback();
  throw error;
}

down: async (queryInterface) => { await queryInterface.removeColumn('users', 'verified'); } };

Checkpoint-Based Rollback

module.exports = { up: async (queryInterface, Sequelize) => { // Create backup table await queryInterface.sequelize.query( 'CREATE TABLE users_backup AS SELECT * FROM users' );

try {
  // Perform migration
  await queryInterface.addColumn('users', 'new_field', {
    type: Sequelize.STRING
  });

  // Verify migration
  const [result] = await queryInterface.sequelize.query(
    "SELECT COUNT(*) as count FROM users WHERE new_field IS NULL"
  );

  if (result[0].count > 0) {
    throw new Error('Migration verification failed');
  }

  // Drop backup
  await queryInterface.dropTable('users_backup');
} catch (error) {
  // Restore from backup
  await queryInterface.sequelize.query('DROP TABLE users');
  await queryInterface.sequelize.query(
    'CREATE TABLE users AS SELECT * FROM users_backup'
  );
  await queryInterface.dropTable('users_backup');
  throw error;
}

} };

Zero-Downtime Migrations

Blue-Green Deployment Strategy

// 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

// 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
    }
  });
}

} };

Resources

references/orm-switching.md: ORM migration guides
references/schema-migration.md: Schema transformation patterns
references/data-transformation.md: Data migration scripts
references/rollback-strategies.md: Rollback procedures
assets/schema-migration-template.sql: SQL migration templates
assets/data-migration-script.py: Data migration utilities
scripts/test-migration.sh: Migration testing script

Best Practices

Always Provide Rollback: Every up() needs a down()
Test Migrations: Test on staging first
Use Transactions: Atomic migrations when possible
Backup First: Always backup before migration
Small Changes: Break into small, incremental steps
Monitor: Watch for errors during deployment
Document: Explain why and how
Idempotent: Migrations should be rerunnable

Common Pitfalls

Not testing rollback procedures
Making breaking changes without downtime strategy
Forgetting to handle NULL values
Not considering index performance
Ignoring foreign key constraints
Migrating too much data at once

database-migration

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