Migration Generator Skill

Create database migrations from model changes, schema diffs, and migration best practices.

Instructions

You are a database migration expert. When invoked:

1. Detect Schema Changes:

   • Compare current schema with desired state
   • Identify added/removed tables and columns
   • Detect modified column types and constraints
   • Find changed indexes and foreign keys

2. Generate Migration Files:

   • Create forward (up) and backward (down) migrations
   • Use ORM-specific migration format when applicable
   • Include data migrations when needed
   • Handle edge cases and potential data loss

3. Ensure Safety:

   • Prevent accidental data deletion
   • Add rollback capability
   • Include validation steps
   • Warn about breaking changes

4. Best Practices:

   • Make migrations atomic and reversible
   • Avoid destructive operations in production
   • Test migrations on staging first
   • Keep migrations small and focused

Supported Frameworks

• SQL: Raw SQL migrations (PostgreSQL, MySQL, SQLite)
• Node.js: Prisma, TypeORM, Sequelize, Knex.js
• Python: Alembic, Django migrations, SQLAlchemy
• Ruby: Rails Active Record Migrations
• Go: golang-migrate, goose
• PHP: Laravel migrations, Doctrine

Usage Examples

@migration-generator Add user email verification
@migration-generator --from-diff
@migration-generator --rollback
@migration-generator --data-migration
@migration-generator --zero-downtime

Raw SQL Migrations

PostgreSQL - Add Table

-- migrations/001_create_users_table.up.sql
CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  username VARCHAR(50) UNIQUE NOT NULL,
  email VARCHAR(255) UNIQUE NOT NULL,
  password_hash VARCHAR(255) NOT NULL,
  active BOOLEAN DEFAULT true NOT NULL,
  created_at TIMESTAMP DEFAULT NOW() NOT NULL,
  updated_at TIMESTAMP DEFAULT NOW() NOT NULL
);

-- Create indexes
CREATE INDEX idx_users_email ON users(email);
CREATE INDEX idx_users_username ON users(username);
CREATE INDEX idx_users_active ON users(active) WHERE active = true;

-- Add comments
COMMENT ON TABLE users IS 'Application users';
COMMENT ON COLUMN users.email IS 'User email address (unique)';

-- migrations/001_create_users_table.down.sql
DROP TABLE IF EXISTS users CASCADE;

Add Column with Default Value

-- migrations/002_add_email_verified.up.sql
-- Step 1: Add column as nullable
ALTER TABLE users ADD COLUMN email_verified BOOLEAN;

-- Step 2: Set default value for existing rows
UPDATE users SET email_verified = false WHERE email_verified IS NULL;

-- Step 3: Make column NOT NULL
ALTER TABLE users ALTER COLUMN email_verified SET NOT NULL;

-- Step 4: Set default for future rows
ALTER TABLE users ALTER COLUMN email_verified SET DEFAULT false;

-- migrations/002_add_email_verified.down.sql
ALTER TABLE users DROP COLUMN email_verified;

Modify Column Type (Safe)

-- migrations/003_increase_email_length.up.sql
-- Safe: increasing varchar length
ALTER TABLE users ALTER COLUMN email TYPE VARCHAR(320);

-- migrations/003_increase_email_length.down.sql
-- Warning: May fail if data exceeds old limit
ALTER TABLE users ALTER COLUMN email TYPE VARCHAR(255);

Add Foreign Key

-- migrations/004_create_orders.up.sql
CREATE TABLE orders (
  id SERIAL PRIMARY KEY,
  user_id INTEGER NOT NULL,
  total_amount DECIMAL(10,2) NOT NULL CHECK (total_amount >= 0),
  status VARCHAR(20) DEFAULT 'pending' NOT NULL,
  created_at TIMESTAMP DEFAULT NOW() NOT NULL,
  updated_at TIMESTAMP DEFAULT NOW() NOT NULL,

  CONSTRAINT fk_orders_user_id
    FOREIGN KEY (user_id)
    REFERENCES users(id)
    ON DELETE CASCADE
);

-- Indexes for foreign keys and common queries
CREATE INDEX idx_orders_user_id ON orders(user_id);
CREATE INDEX idx_orders_status ON orders(status);
CREATE INDEX idx_orders_created_at ON orders(created_at);

-- Composite index for common query pattern
CREATE INDEX idx_orders_user_status ON orders(user_id, status);

-- migrations/004_create_orders.down.sql
DROP TABLE IF EXISTS orders CASCADE;

Rename Column (Safe)

-- migrations/005_rename_password_column.up.sql
-- Step 1: Add new column
ALTER TABLE users ADD COLUMN password_hash_new VARCHAR(255);

-- Step 2: Copy data
UPDATE users SET password_hash_new = password_hash;

-- Step 3: Make NOT NULL
ALTER TABLE users ALTER COLUMN password_hash_new SET NOT NULL;

-- Step 4: Drop old column
ALTER TABLE users DROP COLUMN password_hash;

-- Step 5: Rename new column
ALTER TABLE users RENAME COLUMN password_hash_new TO password_hash;

-- migrations/005_rename_password_column.down.sql
-- Reversible using same pattern
ALTER TABLE users ADD COLUMN password_hash_old VARCHAR(255);
UPDATE users SET password_hash_old = password_hash;
ALTER TABLE users ALTER COLUMN password_hash_old SET NOT NULL;
ALTER TABLE users DROP COLUMN password_hash;
ALTER TABLE users RENAME COLUMN password_hash_old TO password_hash;

ORM Migration Examples

Prisma

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