Database Migration

Overview

Safe database schema evolution for production apps with user data. Core principle Migrations are immutable after shipping. Make them additive, idempotent, and thoroughly tested.

Example Prompts

These are real questions developers ask that this skill is designed to answer:

1. "I need to add a new column to store user preferences, but the app is already live with user data. How do I do this safely?"

→ The skill covers safe additive patterns for adding columns without losing existing data, including idempotency checks

2. "I'm getting 'cannot add NOT NULL column' errors when I try to migrate. What does this mean and how do I fix it?"

→ The skill explains why NOT NULL columns fail with existing rows, and shows the safe pattern (nullable first, backfill later)

3. "I need to change a column from text to integer. Can I just ALTER the column type?"

→ The skill demonstrates the safe pattern: add new column → migrate data → deprecate old (NEVER delete)