Support multiple database migrations when running pending migrations.

[tgxworld]

Summary

Support multiple database migrations when running pending migrations.

Also fixes the issue where running pending migrations does not dump the
schema.

Other Information

Related to #34788 and #26542

[tgxworld]

cc @gsamokovarov @vipulnsward @kaspth

[tgxworld]

I tried out Rails::Command.invoke("db:migrate") but kept getting Don't know how to build task 'rails --task' (See the list of available tasks with rails --tasks) when running the railties test suite.

[jonathanhefner]

This feels a little backwards to me. What about updating ActiveRecord::Tasks::DatabaseTasks#migrate to handle multiple databases (or adding a new method, if necessary)? Then the db:migrate Rake task can be refactored to delegate to that method.

[tgxworld]

I tried out Rails::Command.invoke("db:migrate") but kept getting Don't know how to build task 'rails --task' (See the list of available tasks with rails --tasks) when running the railties test suite.

Rails::Command.invoke("db:migrate") works perfectly in a Rails app but the railties test suite has a different behavior which I can't seem to figure out.

[tgxworld]

Test failures don't seem to be related. Seeing it happen on the master branch as well: https://buildkite.com/rails/rails/builds/70429

[tgxworld]

@jonathanhefner It turns out adding a migrate_all to DatabaseTasks was pretty straight forward.

[tgxworld]

Build seems to be consistently broken?

ERROR: error pulling image configuration: Get https://docker-images-prod.s3.amazonaws.com/registry-

I'll retry the build after a few hours.

[hahmed]

Do we want the migrations to run for all the databases?

I read in a number of PRs that sometimes migrations may be applied to one database but not the other.

[tgxworld]

If a migration is created in the migrations path of a particular database, I believe we should run those migrations