When you are developing rails engine which has connects with two databases you don't have ordinary rails tasks like db:migrate db:structure:load etc. They are moved into app namespace.

so instead of rake db:migrate you need to right rake app:db:migrate.

when you use gem with railtie that has rake tasks in rails engine those task namespaced into app too.
Problem appears when you want to run another rake task inside of yours. For example when we inside app namespace we need to run app:db:migrate instead of `db:migrate.

in this PR I've solved this problem in a same way as active_record does - just call tasks using name related to current db namespace