created_at- Automatically gets set to the current date and time when the record is first created.updated_at- Automatically gets set to the current date and time whenever the record is updated.lock_version- Adds to a model.type- Specifies that the model uses .(association_name)_type- Stores the type for .(table_name)_count- Used to cache the number of belonging objects on associations. For example, acomments_countcolumn in anArticleclass that has many instances ofCommentwill cache the number of existent comments for each article.