Migrations

We have a Starship entity... but no starship table! The solution? Database migrations!

Create our first migration by running:

symfony console make:migration

Success! This didn't add the actual table, but it did create a new file in the migrations/ directory. Let's check it out!

Ooh, it's a PHP class where the up() method holds the SQL to create our table. What's neat is how this was created: Doctrine compared the current state of our entities to the database and generated the SQL needed to make them match. Wow!

There's also a down() method... because migrations can be reversed, but I've never done that, so I don't worry about down().

One thing to note about the SQL: it's in the format of the database platform you're using. In our case, Postgres-specific SQL. If using SQLite, you'd see SQLite-specific SQL.

If you want, add a note about what this does in getDescription(): return 'Add starship table'.

Checking the Migration Status

Pop over to the terminal and run:

symfony console doctrine:migrations:list

The output is a bit wonky but we can see our migration class and its description. The status is not migrated because we haven't executed it yet. Let's do that!

symfony console doctrine:migrations:migrate

Are we sure we want to continue? Yes! Success! Try:

symfony console doctrine:migrations:list

again. Status: migrated!

How Migrations Work

But how does Doctrine track which migrations have been run? It creates a doctrine_migration_versions table, then inserts a row for each migration after it's executed.

We can see it! Run:

symfony console doctrine:query:sql 'select * from doctrine_migration_versions'

Look at that! There's our migration class, when it was executed, how long it took, and the migration's favorite color! Ok, not that last one.

Does this mean we have our starship table? Run another raw SQL query to find out!

symfony console doctrine:query:sql 'select * from starship'

The query yielded an empty result set.

Green means good, right? Yup! This tells us that there's no data in the starship table... but it does exist!

Entity class check: ✅ Database table check: ✅ Data in the database? Let's learn how to do that next!