ActualDbSchema

Does switching between branches in your Rails app mess up the DB schema?

Keep the DB schema actual across branches in your Rails project. Just install actual_db_schema gem and run db:migrate in branches as usual. It automatically rolls back the phantom migrations (non-relevant to the current branch). No additional steps are needed. It works with both schema.rb and structure.sql.

Why ActualDbSchema

Still not clear why it's needed? To grasp the purpose of this gem and the issue it addresses, review the problem definition outlined below.

The problem definition

Imagine you're working on branch A. You add a not-null column to a database table with a migration. You run the migration. Then you switch to branch B. The code in branch B isn't aware of this newly added field. When it tries to write data to the table, it fails with an error null value provided for non-null field. Why? The existing code is writing a null value into the column with a not-null constraint.

Here's an example of this error:

ActiveRecord::NotNullViolation:
  PG::NotNullViolation: ERROR:  null value in column "log" of relation "check_results" violates not-null constraint
  DETAIL:  Failing row contains (8, 46, success, 2022-10-16 21:47:21.07212, 2022-10-16 21:47:21.07212, null).

Furthermore, the db:migrate task on branch B generates an irrelevant diff on the schema.rb file, reflecting the new column added in branch A.

To fix this, you need to switch back to branch A, find the migration that added the problematic field, and roll it back. We'll call it a phantom migration. It's a pain, especially if you have a lot of branches in your project because you have to remember which branch the phantom migration is in and then manually roll it back.

With actual_db_schema gem you don't need to care about that anymore. It saves you time by handling all this dirty work behind the scenes automatically.

How it solves the issue

This gem stores all run migrations with their code in the tmp/migrated folder. Whenever you perform a schema dump, it rolls back the phantom migrations.

The phantom migrations list is the difference between the migrations you've executed (in the tmp/migrated folder) and the current ones (in the db/migrate folder).

Therefore, all you do is run rails db:migrate in your current branch. actual_db_schema will ensure the DB schema is up-to-date. You'll never have an inaccurate schema.rb file again.

Installation

Add this line to your application's Gemfile:

group :development do
  gem "actual_db_schema"
end

And then execute:

$ bundle install

If you cannot commit changes to the repo or Gemfile, consider the local Gemfile installation described in this post.

Usage

Just run rails db:migrate inside the current branch. It will roll back all phantom migrations for all configured databases in your database.yml.

Warning

This solution implies that all migrations are reversible. The irreversible migrations should be solved manually. At the moment, the gem ignores them. You will see warnings in the terminal for each irreversible migrations.

The gem offers the following rake tasks that can be manually run according to your preferences:

• rails db:rollback_branches - run it to manually rolls back phantom migrations.
• rails db:rollback_branches:manual - run it to manually rolls back phantom migrations one by one.
• rails db:phantom_migrations - displays a list of phantom migrations.

Accessing the UI

The UI for managing migrations is enabled automatically. To access the UI, simply navigate to the following URL in your web browser:

http://localhost:3000/rails/phantom_migrations

This page displays a list of phantom migrations for each database connection and provides options to view details and rollback them.

UI options

By default, the UI is enabled in the development environment. If you prefer to enable the UI for another environment, you can do so in two ways:

1. Using Environment Variable

Set the environment variable ACTUAL_DB_SCHEMA_UI_ENABLED to true:

export ACTUAL_DB_SCHEMA_UI_ENABLED=true

2. Using Initializer

Add the following line to your initializer file (config/initializers/actual_db_schema.rb):

ActualDbSchema.config[:ui_enabled] = true

With this option, the UI can be disabled for all environments or be enabled in specific ones.

Disabling Automatic Rollback

By default, the automatic rollback of migrations is enabled. If you prefer to perform manual rollbacks, you can disable the automatic rollback in two ways:

1. Using Environment Variable

Set the environment variable ACTUAL_DB_SCHEMA_AUTO_ROLLBACK_DISABLED to true:

export ACTUAL_DB_SCHEMA_AUTO_ROLLBACK_DISABLED=true

2. Using Initializer

Add the following line to your initializer file (config/initializers/actual_db_schema.rb):

ActualDbSchema.config[:auto_rollback_disabled] = true

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test 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 do the following in the order:

• update the version number in version.rb;
• update the CHANGELOG;
• bundle install to update Gemfile.lock;
• make the commit and push;
• run bundle exec rake release. This will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org;
• announce the new release on GitHub.

Running Tests with Specific Rails Versions

The following versions can be specifically tested using Appraisal

• 6.0
• 6.1
• 7.0
• 7.1
• edge

To run tests with a specific version of Rails using Appraisal:

• Run all tests with Rails 6.0:

  bundle exec appraisal rails.6.0 rake test

• Run tests for a specific file:

  bundle exec appraisal rails.6.0 rake test TEST=test/rake_task_test.rb

• Run a specific test:

  bundle exec appraisal rails.6.0 rake test TEST=test/rake_task_test.rb TESTOPTS="--name=/db::db:rollback_branches#test_0003_keeps/"

Contributing

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

License

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

Code of Conduct

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