Pessimistic Locking Concern for AR

lockable.rb

module Lockable
  extend ActiveSupport::Concern

  LOCKABLE = { on: :self }

  def transaction_has_lock_for(target)
    (transaction_get_locks || []).include?(target)
  end

  def transaction_add_lock(lock)
    locks = transaction_get_locks
    if locks
      locks << lock
    else
      ActiveRecord::Base.connection.current_transaction.instance_variable_set('@_locks'.freeze, [lock])
    end
  end

  def transaction_get_locks
    ActiveRecord::Base.connection.current_transaction.instance_variable_get('@_locks'.freeze)
  end

  def lock_target
    if self.class::LOCKABLE[:on] == :self
      self
    else
      current = self
      if self.class::LOCKABLE[:through]
        Array.wrap(self.class::LOCKABLE[:through]).each { |item| current = current.send(item) }
      end
      current.send(self.class::LOCKABLE[:on])
    end
  end

  def acquire_pessimistic_lock!
    # Note that lock! functions *will* clobber Dirty changes
    unless transaction_has_lock_for(lock_target)
      # _future_state = lock_target.changes.each_with_object({}) { |(key, val), h| h[key] = val[1]}
      lock = lock_target.lock!
      transaction_add_lock(lock)
      # _future_state.each { |attr, value| lock.send(:write_attribute, attr, value) }
    end
    true
  end
end