Establish a connection to another database only in a block?

Question

In a rails application, I have this code in pure ruby :

class LinkCreator
  attr_accessor :animal

  def initialize(animal:)
    @animal = animal
  end

  de         


        

Answer 1

You can perform some queries within a block. First, define some module which will extend ActiveRecord, as below. This is a part of code used in production to change db connection per each request as well as to temporarily switch db to perform some queries within another database.

# RAILS_ROOT/lib/connection_switch.rb
module ConnectionSwitch
  def with_db(connection_spec_name)
    current_conf = ActiveRecord::Base.connection_config

    begin
      ActiveRecord::Base.establish_connection(db_configurations[connection_spec_name]).tap do
        Rails.logger.debug "\e[1;35m [ActiveRecord::Base switched database] \e[0m #{ActiveRecord::Base.connection.current_database}"
      end if database_changed?(connection_spec_name)

      yield
    ensure
      ActiveRecord::Base.establish_connection(current_conf).tap do
        Rails.logger.debug "\e[1;35m [ActiveRecord::Base switched database] \e[0m #{ActiveRecord::Base.connection.current_database}"
      end if database_changed?(connection_spec_name, current_conf)
    end

  end

  private
  def database_changed?(connection_spec_name, current_conf = nil)
    current_conf = ActiveRecord::Base.connection_config unless current_conf
    current_conf[:database] != db_configurations[connection_spec_name].try(:[], :database)
  end

  def db_configurations
    @db_config ||= begin
      file_name =  "#{Rails.root}/config/database.yml"
      if File.exists?(file_name) || File.symlink?(file_name)
        config ||= HashWithIndifferentAccess.new(YAML.load(ERB.new(File.read(file_name)).result))
      else
        config ||= HashWithIndifferentAccess.new
      end

      config
    end
  end
end
ActiveRecord.send :extend, ConnectionSwitch

Now you can use it as below:

ActiveRecord.with_db("db_connection_name") do
  # some queries to another db
end