Rails: Loading schema into secondary database

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}"