Add database specific setup and reset tasks for multidb configurations

[ryanahall]

Summary

This is an attempt at enabling database specific setup and reset tasks. We use multiple databases pretty extensively and would like to avoid resetting all databases at once. This change adds database specific setup and reset tasks under each namespace. The default setup and reset tasks remain unchanged aside from their descriptions.

One thing that may be problematic is that the db:seed task is database agnostic, which means that the database scoped tasks will end up seeding everything. Would it be possible to seed only a specific database? At first glance, it doesn't seem like this is the case because the seed files could reference any active record model.

This results in the following tasks for an example configuration with two databases: primary and events.

rails db:reset                                  # Drops and recreates all databases from their schema for the current environment and loads the seeds
rails db:reset:events                           # Drops and recreates the events database from its schema for the current environment and loads the seeds
rails db:reset:primary                          # Drops and recreates the primary database from its schema for the current environment and loads the seeds
rails db:setup                                  # Creates all databases, loads all schemas, and initializes with the seed data (use db:reset to also drop all databases first)
rails db:setup:events                           # Creates the events database, loads the schema, and initializes with the seed data (use db:reset:events to also drop the database first)
rails db:setup:primary                          # Creates the primary database, loads the schema, and initializes with the seed data (use db:reset:primary to also drop the database first)

Other Information

[eileencodes]

Thanks for the PR @ryanahall - can you add some tests in railties/test/application/rake/multi_dbs_test.rb. Active Record also needs a CHANGELOG entry.

[eileencodes]

Will seed try to load seeds on all the dbs or just the named ones here?

[ryanahall]

Thanks for reviewing @eileencodes! This will unfortunately seed all dbs. From my understanding of db/seeds.rb, it can reference any ActiveRecord model and there's no scope to which database will be touched. I don't think there's a way to enforce that a seed file will only touch a single database, but I could be mistaken.

[ryanahall]

Thanks for the PR @ryanahall - can you add some tests in railties/test/application/rake/multi_dbs_test.rb. Active Record also needs a CHANGELOG entry.

Sure thing, I'll look into adding some tests and updating the CHANGELOG today. Thanks again!

[eileencodes]

Can you squash your commits into one?

[ryanahall]

Can you squash your commits into one?

Sure thing @eileencodes, I rebased and squashed my commits.