Database Migration Creator

---
description: Create a database migration with up/down and rollback safety
allowed-tools: Read, Write, Bash(ls), Bash(cat *), Glob
---

# Database Migration Creator

Generate a safe, reversible database migration based on the requested schema change.

## Arguments

- `$ARGUMENTS` — description of the schema change (e.g. "add email_verified boolean column to users table")

## Steps

1. Identify the migration tool in use by checking for:
   - `prisma/` directory → Prisma Migrate
   - `drizzle/` or `drizzle.config.*` → Drizzle Kit
   - `migrations/` with numbered SQL files → raw SQL migrations
   - `knexfile.*` → Knex.js migrations
   - `sequelize` in package.json → Sequelize CLI
2. Read the existing schema or recent migrations to understand:
   - Current table structure and relationships
   - Naming conventions (snake_case vs camelCase, plural vs singular)
   - Whether timestamps (`created_at`, `updated_at`) are standard
3. Generate the migration file in the correct format for the detected tool.

## Migration requirements

### Up migration
- Add columns with sensible defaults for existing rows.
- Create indexes for columns that will be queried frequently.
- Add foreign key constraints with appropriate `ON DELETE` behavior.
- Use `NOT NULL` with defaults rather than nullable columns where possible.

### Down migration
- Reverse every change made in the up migration.
- Drop indexes before dropping columns.
- Handle data loss warnings (e.g. dropping a column with data).

### Safety checks
- Never drop a table or column in the up migration without explicit confirmation in `$ARGUMENTS`.
- For large tables, note that `ALTER TABLE` may lock the table — suggest batched approaches if applicable.
- Include a comment block at the top with:
  - Description of the change
  - Tables affected
  - Whether the migration is reversible
  - Estimated risk level (low/medium/high)

## Rules

- Follow the project's existing naming convention for migration files.
- Never modify existing migration files — always create new ones.
- Include the current timestamp or sequential number in the filename as per project convention.
- If adding an enum type, create it in a separate migration that runs first.