Rails: Loading schema into secondary database - ruby-on-rails

Question

How does one load a schema into a secondary database? It seems that the ability to set a secondary database connection while maintaining the main ActiveRecord::Base.connection is not supported in Rails.
Domain Definition
We have models using a secondary database. Our primary database is MySQL, the secondary database is PostgreSQL. To use the ActiveRecord documentation's example:
|
+-- Book
| |
| +-- ScaryBook
| +-- GoodBook
+-- Author
+-- BankAccount
Where Book is abstract and uses establish_connection to connect to Postgres.
When dealing with the database, we can either use ActiveRecord::Base.connection or Book.connection.
Schema dump
To wit: Rails database tasks in the schema namespace allow us to dump the schema as so:
ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, file)
Which would allow me to do the following:
ActiveRecord::SchemaDumper.dump(Book.connection, file)
Problem: Schema Load
However, the load task holds no such ability. It merely evaluates the schema file as a whole:
desc 'Load a schema.rb file into the database'
task :load => :environment do
file = ENV['SCHEMA'] || "#{Rails.root}/db/schema.rb"
if File.exists?(file)
load(file)
else
abort %{#{file} doesn't exist yet. Run "rake db:migrate" to create it then try again. If you do not intend to use a database, you should instead alter #{Rails.root}/config/application.rb to limit the frameworks that will be loaded}
end
end
Where the schema file runs ActiveRecord::Schema.define without the connection definition. (Noting that the define method runs in the context of "the current connection adapter").
How do I change that "current connection adapter" without doing an ad-hoc ActiveRecord::Base.establish_connection, which is not what I want to do? I essentially want to run ActiveRecord::Schema.define in the context of Book.connection.
Edit: I'll note that I need a programmatic solution outside of running rake tasks, which is why I'm looking within the rake tasks to see what they're actually doing.

Answer 1

How to dump schema:
ActiveRecord::Base.establish_connection "custom_db_#{Rails.env}".to_sym
File.open Rails.root.join('db/schema_custom_db.rb'), 'w:utf-8' do |file|
ActiveRecord::SchemaDumper.dump ActiveRecord::Base.connection, file
end
How to load schema:
ActiveRecord::Tasks::DatabaseTasks.load_schema_current :ruby, Rails.root.join('db/schema_custom_db.rb'), "custom_db_#{Rails.env}"

Answer 2

I've been struggling recently with trying to just use ActiveRecord. I can load migrations and dump schema but when it comes to loading a schema I run into a similar problem and it's not a Rails or Rake one. Just FYI.
I know you don't want do this standalone but I'm trying.
Please note see this post:
rake db:schema:load vs. migrations
I'm still obsessed with trying to do it on my own without Rails or Rake help so that I gain a better understanding of how ActiveRecord works.
I made a very minimal Rails structure just to generate migrations.
file structure:
Rakefile
Gemfile
/bin
bundle
rake
rails
/config
application.rb
boot.rb
database.yml
environment.rb
/db
/migrate
development.sqlite3
schema.rb
bin/rails generate migration CreateSystemSettings
and I get a file 20150207170924_create_system_settings.rb in the db/migrate folder.
bin/rake db:migrate
== 20150204070000 DropArticles: migrating
== 20150204070000 DropArticles: migrated (0.0001s)
== 20150207163123 AddPartNumberToProducts: migrating
== 20150207163123 AddPartNumberToProducts: migrated (0.0000s)
== 20150207163909 ChangeSystemSettings: migrating
== 20150207163909 ChangeSystemSettings: migrated (0.0000s)
== 20150207170924 CreateSystemSettings: migrating
-- create_table(:system_settings)
-> 0.0085s
== 20150207170924 CreateSystemSettings: migrated (0.0199s)
so that works
Update pending