ActiveRecord-without-Rails | ActiveRecord CRUD tasks using Ruby | Job Scheduling library

For a new project I thought, why not skip rails and do more myself. Sadly I fail at a really simple problem.

I found out already that I need to use ActiveRecord::Base.connection.create_database('backend') after I set the connection with ActiveRecord::Base.establish_connection to create the database.

Sadly the error I get is really annoying since it tells me it can not create the database, because it does not exist: ActiveRecord::NoDatabaseError (Unknown database 'backend').

I use docker-compose to host the code and database, hostname/username/password are all correct. It is har to use google since all code examples use rails and tell you to call rake db:create witch I obviously try to create myself while I had this error.