1 after_update callback is wrapped in transaction means:no matter
exception occurs during saving an existing record, or in the
after_update method body,both the existing record and record
manipulation in the after_update body are all rollbacked?
2 class Book < ActiveRecord::Base
validate_associated means: when i invoke book.save to save book and it's
associations,no matter invalidation occurs during saving book self or
saving any association,both book and all the associations don't be
I don't understand these from document.can you help me to make it sure?