Question

In our Rails 3.2.6 app, we have a model attribute named ‘version’ that is incremented at the database level whenever an instance is created or updated (via trigger). However, after we do a successful create or update, the new value set by the database is not being returned to our instance, unless we explicitly do an instance.reload.

Does anyone know of a way to have active record automatically reload the instance after persisting to the database?

Background

In our Rails 3.2.6 app, we have a 3 tables that each have a ‘version’ column. Across all 3 tables, the ‘version’ integer column needs to be incremented during each insert and update, and the ‘version’ must never repeat.

Simple solution: we’ve created a version_sequence in postgres that all 3 tables share. We have a small trigger that updates the version column of any record from these tables with the nextval(‘version_sequence’) value:

  -- Resource Version Sequence
  CREATE SEQUENCE resource_versions_seq;


  -- Resource Version Trigger
  CREATE FUNCTION update_resource_version() RETURNS trigger AS $update_resource_version$
    BEGIN
      NEW.version := nextval('resource_versions_seq');
      RETURN NEW;
    END;
  $update_resource_version$ LANGUAGE plpgsql;

However, when we create, save, or update_attributes in active_record, the new ‘version’ value is not being reloaded after the record is persisted.

Answer 1

How about using the after_save callback? In this callback you could fetch just that field and then set it on the model. Something like this:

class Thing < ActiveRecord::Base
  after_save :refresh_version

  def refresh_version
    self.version = Thing.find(self.id).select(:version)
  end

end