Schema as part of the code.
THE PROBLEM
Code is versioned. Databases are not, unless you make them so.
WHAT THAT PRODUCES
Code expecting a column that does not exist Environments with different structures Nobody able to recreate the database
WHAT TO DO
Describe every structural change as a migration, committed alongside the code.
WHAT EACH MIGRATION NEEDS
How to apply it, and how to reverse it.
WHAT TO NEVER DO
Change a migration that has already run in production.
WHY
The record of what was applied becomes wrong, and environments diverge.
WHAT TO DO INSTEAD
Write a new migration.
WHAT TO BE CAREFUL WITH
Migrations that lock large tables Migrations combining structural and data changes
WHAT TO SEPARATE
Structure from data.
WHAT TO RUN BEFORE MIGRATING PRODUCTION
A backup.
WHAT TO TEST
Applying and reversing, on a copy with realistic volume.
WHAT TO ORDER CAREFULLY
Deployments involving both code and schema changes.
