Migration

Each one is numbered, and each changes the shape of your database, its schema: add a column, rename a table, add an index. The file stays in your project, so the same change runs the same way on your machine and on the copy your customers reach.

You will run into migrations the first time you want to store something new, a tracking number, a note on a draft, and the app refuses because there is nowhere to put it.

The usual mistake is editing a migration that already ran. It will not run again. Write a new one on top of it instead.