App Platform - Database connection protocol "mysql" instead of "mysql2" for Rails app

I’m trying to set-up my first application using the App Platform - it’s a Ruby on Rails application that I’m trying to link to an existing MySQL database.

The default behaviour sets a DATABASE_URL environment variable with the correct connection string - it begins mysql://

However, in Ruby on Rails, this tries to use the older “mysql” gem, instead of the “mysql2” gem. (The older gem isn’t compiling for me.)

I believe this would work if DATABASE_URL began with mysql2:// - but I can’t seem to find any way to change that protocol.

I suspect I could remove the environment variable and configure all the parameters manually, but this seems a shame when the built-in behaviour is so very close to what I need!

Any advice warmly received - many thanks!