database-migrations

name	database-migrations
description	Creates safe database migrations with proper indexes and rollback strategies. Use when creating tables, adding columns, creating indexes, handling zero-downtime migrations, or when user mentions migrations, schema changes, or database structure.
allowed-tools	Read, Write, Edit, Bash, Glob, Grep

Database Migration Patterns for Rails 8

Overview

Safe database migrations are critical for production stability:

• Zero-downtime deployments
• Reversible migrations
• Proper indexing
• Data integrity constraints

Quick Start

bin/rails generate migration AddStatusToEvents status:integer
bin/rails db:migrate
bin/rails db:rollback
bin/rails db:migrate:status

Safety Checklist

Migration Safety:
- [ ] Migration is reversible (has down or uses change)
- [ ] Large tables use batching for updates
- [ ] Indexes added concurrently (if needed)
- [ ] Foreign keys have indexes
- [ ] NOT NULL added in two steps (for existing columns)
- [ ] Default values don't lock table
- [ ] Tested rollback locally

Safe Migration Patterns

Pattern 1: Add Column (Safe)

class AddStatusToEvents < ActiveRecord::Migration[8.0]
  def change
    add_column :events, :status, ,  ,