Setup second database with migrations path pointing to bundled engine

Question

We have a Rails engine (developed in-house) that's bundled into our main Rails app. To reduce the load on our current database server; we want to use the multiple databases feature in Rails 6. I've defined a second database in config/database.yml:

development
  primary:
    <<: *default
    database: primary-dev
  engine:
    <<: *default
    database: engine-dev
    migrations_paths: <what should this be set to?>

and the Rails app recognises that another database has been defined. However, what do I set migrations_paths to, so that the second database uses the migrations defined in the engine?

I've tried bundle exec rails engine:install:migrations to move the migrations into the Rails app, manually moved them to a sub-directory and set migrations_paths to that. However, this seems quite clunky and wondered if there was a different syntax to reference the migrations in the engine?

Should the engine have its own config/database.yml that defines its database? How do I pass the database connection details down from the Rails app to the engine? Is that just part of the initialisation of the engine?

Answer 1

You can find the migration path with the following command :

MyEngine::Engine.paths['db/migrate'].to_a.first

for an engine named 'MyEngine'.

You do not need to copy migrations if you add the migrations_paths to your database configuration.