Migrations

We briefly covered migrations before, but now it's a good time to review how they work in a bit more detail.

We have prepared a video for you to watch: https://www.youtube.com/watch?v=BNgtAloCwHg

What are migrations?

Migrations are a way to perform programmatic changes to your database when you might not have direct access to the database. Ideally you shouldn't need to work with pgAdmin and postgres directly for this task.

In a nutshell, migrations are just SQL files being executed at most once in a certain order. It is important to remember that migrations are only ever run once, and exactly once. To achieve that, we need to keep track of which migrations have already been run when triggering a migration, by creating a separate migrations table.

How do migrations work?

In our track, this has already been handled in the migrate script you've already added, so you don't need to do anything. Feel free to have a read through and see if you can understand it better.

You can think of each migration as a small incremental step someone could take to re-create the structure of your database, and be up-to-date with what you want their. Each new migration makes a new change that applies on top of the last change. It is also a log of all the changes that were applied in the past, so they can serve as documentation too.

Once a migration has been performed (and the SQL it contained has been executed), you shouldn't change it. You will need to add a new migration and continue applying your desired changes that way.