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.

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.

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.

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.

Add this line to your application's Gemfile:

group :development do
  gem "actual_db_schema"
end

And then execute:

$ bundle install

Just run rails db:migrate inside the current branch.

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:phantom_migrations - displays a list of phantom migrations.

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.

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.

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

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