README

This application is to demonstrate how to connect to multiple databases from a rails application.

Steps

1. create a rails application

2. along with database.yml add the database config through a secondary yml file ex:

#database_sec.yml

development: adapter: postgresql encoding: unicode pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %> database: multiple_db_demo_development_sec

3. add an initializer to load the database configuration config/initializers/db_sec.rb DB_SEC = YAML::load(ERB.new(File.read(Rails.root.join("config","database_sec.yml"))).result)[Rails.env]

4. Add folder structure for managing migrations, schema.rb, seeds.rb and schema_migrations multiple_db_demo

   • db
     • migrate
     • schema.rb
   • db_sec
     • migrate
     • schema.rb

5. create tasks and namespaces to manage db_sec specific tasks

#lib/tasks/db_sec.rake task spec: ["sec:db:test:prepare"]

namespace :sec do

namespace :db do |ns|

  task :drop do
    Rake::Task["db:drop"].invoke
  end

  task :create do
    Rake::Task["db:create"].invoke
  end

  task :setup do
    Rake::Task["db:setup"].invoke
  end

  task :migrate do
    Rake::Task["db:migrate"].invoke
  end

  task :rollback do
    Rake::Task["db:rollback"].invoke
  end

  task :seed do
    Rake::Task["db:seed"].invoke
  end

  task :version do
    Rake::Task["db:version"].invoke
  end

  namespace :schema do
    task :load do
      Rake::Task["db:schema:load"].invoke
    end

    task :dump do
      Rake::Task["db:schema:dump"].invoke
    end
  end

  namespace :test do
    task :prepare do
      Rake::Task["db:test:prepare"].invoke
    end
  end

  # append and prepend proper tasks to all the tasks defined here above
  ns.tasks.each do |task|
    task.enhance ["sec:set_custom_config"] do
      Rake::Task["sec:revert_to_original_config"].invoke
    end
  end
end

task :set_custom_config do
  # save current vars
  @original_config = {
    env_schema: ENV['SCHEMA'],
    config: Rails.application.config.dup
  }

  # set config variables for custom database
  ENV['SCHEMA'] = "db_sec/schema.rb"
  Rails.application.config.paths['db'] = ["db_sec"]
  Rails.application.config.paths['db/migrate'] = ["db_sec/migrate"]
  Rails.application.config.paths['db/seeds'] = ["db_sec/seeds.rb"]
  Rails.application.config.paths['config/database'] = ["config/database_sec.yml"]
end

task :revert_to_original_config do
  # reset config variables to original values
  ENV['SCHEMA'] = @original_config[:env_schema]
  Rails.application.config = @original_config[:config]
end

end

5. Add generator to handle the rails generators

class SecMigrationGenerator < ActiveRecord::Generators::MigrationGenerator source_root File.join(File.dirname(ActiveRecord::Generators::MigrationGenerator.instance_method(:create_migration_file).source_location.first), "templates")

def create_migration_file
  set_local_assigns!
  validate_file_name!
  migration_template @migration_template, "db_sec/migrate/#{file_name}.rb"
end

end