I have read a few books on OOP DDD/PoEAA/Gang of Four and none of them seem to cover the topic of validation - it seems to be always assumed that data is valid.

I gather from the answers to this post (http://stackoverflow.com/questions/1651964/oop-design-question-validating-properties) that a client should only attempt to set a valid property value on a domain object.

This person has asked a similar question that remains unanswered: http://bytes.com/topic/php/answers/789086-php-oop-setters-getters-data-validation#post3136182

So how do you ensure it is valid? Do you have a 'validator method' alongside every getter and setter?

• isValidName()
• setName()
• getName()

I seem to be missing some key basic knowledge about OOP data validation - can you point me to a book that covers this topic in detail? - ie. covering different types of validation / invariants/ handling feedback / to use Exceptions or not etc