PlanetScale Rails

Rake tasks for easily running Rails migrations against PlanetScale database branches.

For information on how to connect your Rails app to PlanetScale, please see our guide here.

The rake tasks allow you to use local MySQL for development. When you're ready to make a schema change, you can create a PlanetScale branch and run migrations against it. See usage for details.

rake psdb:migrate                    # Migrate the database for current environment
rake psdb:rollback                   # Rollback primary database for current environment
rake psdb:schema:load                # Load the current schema into the database

Add this line to your application's Gemfile:

group :development do
  gem 'planetscale_rails'
end

And then execute in your terminal:

bundle install

Make sure you have the pscale CLI installed.

Add the following to your config/application.rb.

if ENV["DISABLE_SCHEMA_DUMP"]
  config.active_record.dump_schema_after_migration = false
end

This will allow the gem to disable schema dumping after running psdb:migrate.

1. Using pscale, create a new branch. This command will create a local .pscale.yml file. You should add it to your .gitignore.

pscale branch switch my-new-branch-name --database my-db-name --create --wait

Tip: In your database settings. Enable "Automatically copy migration data." Select "Rails" as the migration framework. This will auto copy your schema_migrations table between branches.

2. Run your schema migrations against the branch.

bundle exec rails psdb:migrate

If you run multiple databases in your Rails app, you can specify the DB name.

bundle exec rails psdb:migrate:primary

If you make a mistake, you can use bundle exec rails psdb:rollback to rollback the changes on your PlanetScale branch.

3. Next, you can either open the Deploy Request via the UI. Or the CLI.

Via CLI is:

pscale deploy-request create database-name my-new-branch-name

4. To get your schema change to production, run the deploy request. Then, once it's complete, you can merge your code changes into your main branch in git and deploy your application code.

This gem supports working with multi-keyspace PlanetScale databases. When running migrations, Vitess will automatically route the schema change (DDL) to the correct keyspace based on the name of the table being altered.

Creating new tables

For adding a new table, you must specify the keyspace for the table. When running psdb:migrate, this gem will create the table in the correct keyspace. When running the migration locally against plain MySQL, the keyspace will be ignored and the table will be created as normal within the same database.

create_table(:new_table, id: { type: :bigint, unsigned: true }, keyspace: "keyspace-name") do |t|
  t.string :name
end

PlanetScale's deploy requests solve the schema change problem. They make a normally high risk operation, safe. This is done by running your schema change using Vitess's online schema change tools. Once the change is made, a deploy request is also revertible without data loss. None of this is possible when running rails db:migrate directly against your production database.

We recommend using GitHub Actions to automate the creation of PlanetScale branches and deploy requests. Then when you are ready to merge, you can run the deploy request before merging in your code.

When not to use deploy requests

If your application has minimal data and schema changes are a low risk event, then running psdb:migrate directly against production is perfectly fine. As your datasize grows and your application becomes busier, the risk of schema changes increase and we highly recommend using the deploy request flow. It's the best way available to safely migrate your schema.

Before dropping the column in your database, there are a couple steps to take in your application to safely remove the column without any risk to your production application.

1. Remove all references to the column in your code.
2. Add the column name to self.ignored_columns += %w(column_name) in the model. More on ignored_columns.
3. Deploy this code to production. This ensures your application is no longer making use of the column in production and it's removed from the schema cache.
4. Follow the PlanetScale deploy request flow to drop the column.

See the GitHub Actions examples doc for ways to automate your schema migrations with PlanetScale + Actions.

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/planetscale/planetscale_rails. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

The gem is available as open source under the terms of the Apache 2.0 License.

Everyone interacting in the PlanetScale Rails project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.