Miller Start Docs
 

Database

Miller Start is tested with a Postgres database for data storage.

It uses typeorm which supports many other datastores so you should be able to change to another RDBMS if you like.

Database migrations

Miller Start uses typeorm migrations to manage database schema changes. This is a good way to manage database changes in a consistent way.

The steps for modifying the db schema are:

  1. Create a new entity. It must have the .entity.ts suffix.
  2. Build the app - pnpm run build.
  3. Generate a migration - pnpm run db:gen migrations/my-migration-name.
  4. Review the migration does what you expect.
  5. Start the backend - the migration will be run automatically.

Non-destructive migrations

You must ensure your migrations are non-destructive. Postgres allows column renaming but most databases do not. This means if you change the name of a column, type orm will delete the existing data and add a new empty column.

This is not acceptable for production data.

It's up to you to ensure you understand what a migration is doing and that it is non-destructive.

A better approach is to only ever perform additive changes. Instead of modifying an existing column. Treat it as idempotent and add a new column.

Then you can migrate the data from the old column to the new column. Then you can remove the old column later.

Reverting migrations

TypeORM generates both an "up" and "down" migration to support reverting changes. This is useful for development but not for production.

To revert a migration on production, you must add a new migration that reverts the changes. Then run the new migration. Typeorm "Reverting" a migration will not work as expected for checked in code.

If you apply a migration locally and want to revert it, you CAN use pnpm db:revert <migration-name>. But only locally! This will not work on production.