Code Examples for Our Plan for Zero-Downtime Database Transitions with Rails: Part 2.md

These are the code examples referenced in our blog post Our Plan for Zero-Downtime Database Transitions with Rails: Part 2.

ex01-happy-path-after-commit.rb

after_commit :write_active_migrator_destination_model

ex02-happy-path-callback-method.rb

def write_active_migrator_destination_model!
  if ActiveMigrator.config.enabled_checker.call(id)
    ActiveMigrator.config.metric_incrementer.call("active_migrator.#{active_migrator_source_klass.name}.write_active_migrator_destination_model")
    original_record = find_original_model
    if original_record
      active_migrator_destination_model = original_record.find_active_migrator_destination_model
      original_record.transformed_attributes_for_active_migrator.each do |name, value|
        active_migrator_destination_model.send(:write_attribute, name, value)
      end
      active_migrator_destination_model.save!
    else
      active_migrator_destination_model = find_active_migrator_destination_model
      active_migrator_destination_model.destroy unless active_migrator_destination_model.new_record?
    end
  end
end

ex03-happy-path-destination-model.rb

module ActiveMigrator
  class ActiveMigratorDestinationModel < ActiveRecord::Base
    self.abstract_class = true
    # disable STI for this "copy" model
    self.inheritance_column = :_type_disabled
    establish_connection DB_ACTIVE_MIGRATOR_CONFIGURATION[:destination]
  end
end
module ActiveMigrator
  module ActiveMigratorSource
    extend ActiveSupport::Concern
    included do
      @active_migrator_destination_klass_name = "ActiveMigrator::#{self.name}ActiveMigratorDestinationModel"
      eval <<-STR, nil, __FILE__, __LINE__
        ActiveMigrator.send(:remove_const, :#{self.name}ActiveMigratorDestinationModel) if defined?(#{@active_migrator_destination_klass_name})
        class #{@active_migrator_destination_klass_name} < ActiveMigrator::ActiveMigratorDestinationModel
          self.table_name = '#{table_name}'
          self.record_timestamps = false
          self.lock_optimistically = false
        end
      STR
    end
  end
end

ex04-error-cases-after-commit.rb

after_commit :write_active_migrator_destination_model

ex05-error-cases-callback-method.rb

def write_active_migrator_destination_model
  begin
    write_active_migrator_destination_model!
  rescue Exception => e
    ActiveMigrator.config.exception_handler.call(e, active_migrator_source_class: active_migrator_source_klass.name, active_migrator_source_id: id)
  end
  true
end