Database Migrations

# Create empty migration, then edit the SQL manually
npx prisma migrate dev --create-only --name add_email_index

-- migrations/20240115_add_email_index/migration.sql
-- Prisma cannot generate CONCURRENTLY, so we write it manually
CREATE INDEX CONCURRENTLY IF NOT EXISTS idx_users_email ON users (email);

# Generate migration from schema changes
npx drizzle-kit generate

# Apply migrations
npx drizzle-kit migrate

# Push schema directly (dev only, no migration file)
npx drizzle-kit push

import { pgTable, text, timestamp, uuid, boolean } from "drizzle-orm/pg-core";

export const users = pgTable("users", {
  id: uuid("id").primaryKey().defaultRandom(),
  email: text("email").notNull().unique(),
  name: text("name"),
  isActive: boolean("is_active").notNull().default(true),
  createdAt: timestamp("created_at").notNull().defaultNow(),
  updatedAt: timestamp("updated_at").notNull().defaultNow(),
});

# Initialize config file (kysely.config.ts)
kysely init

# Create a new migration file
kysely migrate make add_user_avatar

# Apply all pending migrations
kysely migrate latest

# Rollback last migration
kysely migrate down

# Show migration status
kysely migrate list

// migrations/2024_01_15_001_create_user_profile.ts
import { type Kysely, sql } from 'kysely'

// IMPORTANT: Always use Kysely<any>, not your typed DB interface.
// Migrations are frozen in time and must not depend on current schema types.
export async function up(db: Kysely<any>): Promise<void> {
  await db.schema
    .createTable('user_profile')
    .addColumn('id', 'serial', (col) => col.primaryKey())
    .addColumn('email', 'varchar(255)', (col) => col.notNull().unique())
    .addColumn('avatar_url', 'text')
    .addColumn('created_at', 'timestamp', (col) =>
      col.defaultTo(sql`now()`).notNull()
    )
    .execute()

  await db.schema
    .createIndex('idx_user_profile_avatar')
    .on('user_profile')
    .column('avatar_url')
    .execute()
}

export async function down(db: Kysely<any>): Promise<void> {
  await db.schema.dropTable('user_profile').execute()
}

import { Migrator, FileMigrationProvider } from 'kysely'
import { promises as fs } from 'fs'
import * as path from 'path'
// ESM only — CJS can use __dirname directly
import { fileURLToPath } from 'url'
const migrationFolder = path.join(
  path.dirname(fileURLToPath(import.meta.url)),
  './migrations',
)

// `db` is your Kysely<any> database instance
const migrator = new Migrator({
  db,
  provider: new FileMigrationProvider({
    fs,
    path,
    migrationFolder,
  }),
  // WARNING: Only enable in development. Disables timestamp-ordering
  // validation, which can cause schema drift between environments.
  // allowUnorderedMigrations: true,
})

const { error, results } = await migrator.migrateToLatest()

results?.forEach((it) => {
  if (it.status === 'Success') {
    console.log(`migration "${it.migrationName}" executed successfully`)
  } else if (it.status === 'Error') {
    console.error(`failed to execute migration "${it.migrationName}"`)
  }
})

if (error) {
  console.error('migration failed', error)
  process.exit(1)
}

# Generate migration from model changes
python manage.py makemigrations

# Apply migrations
python manage.py migrate

# Show migration status
python manage.py showmigrations

# Generate empty migration for custom SQL
python manage.py makemigrations --empty app_name -n description

from django.db import migrations

def backfill_display_names(apps, schema_editor):
    User = apps.get_model("accounts", "User")
    batch_size = 5000
    users = User.objects.filter(display_name="")
    while users.exists():
        batch = list(users[:batch_size])
        for user in batch:
            user.display_name = user.username
        User.objects.bulk_update(batch, ["display_name"], batch_size=batch_size)

def reverse_backfill(apps, schema_editor):
    pass  # Data migration, no reverse needed

class Migration(migrations.Migration):
    dependencies = [("accounts", "0015_add_display_name")]

    operations = [
        migrations.RunPython(backfill_display_names, reverse_backfill),
    ]

class Migration(migrations.Migration):
    operations = [
        migrations.SeparateDatabaseAndState(
            state_operations=[
                migrations.RemoveField(model_name="user", name="legacy_field"),
            ],
            database_operations=[],  # Don't touch the DB yet
        ),
    ]

# Create migration pair
migrate create -ext sql -dir migrations -seq add_user_avatar

# Apply all pending migrations
migrate -path migrations -database "$DATABASE_URL" up

# Rollback last migration
migrate -path migrations -database "$DATABASE_URL" down 1

# Force version (fix dirty state)
migrate -path migrations -database "$DATABASE_URL" force VERSION

-- migrations/000003_add_user_avatar.up.sql
ALTER TABLE users ADD COLUMN avatar_url TEXT;
CREATE INDEX CONCURRENTLY idx_users_avatar ON users (avatar_url) WHERE avatar_url IS NOT NULL;

-- migrations/000003_add_user_avatar.down.sql
DROP INDEX IF EXISTS idx_users_avatar;
ALTER TABLE users DROP COLUMN IF EXISTS avatar_url;

Phase 1: EXPAND
  - Add new column/table (nullable or with default)
  - Deploy: app writes to BOTH old and new
  - Backfill existing data

Phase 2: MIGRATE
  - Deploy: app reads from NEW, writes to BOTH
  - Verify data consistency

Phase 3: CONTRACT
  - Deploy: app only uses NEW
  - Drop old column/table in separate migration

Day 1: Migration adds new_status column (nullable)
Day 1: Deploy app v2 — writes to both status and new_status
Day 2: Run backfill migration for existing rows
Day 3: Deploy app v3 — reads from new_status only
Day 7: Migration drops old status column