Validating Foreign Keys
You saw that declarative lists of values for a view object attribute were used to assist users in selecting existing foreign key lookup values. Although these lists are handy for end users, they are not a substitute for the proper validation of the foreign key at the entity object level. For example, some UI components, such as a text box with a pop-up list, allow the user to enter a foreign key value directly. Furthermore, the service may be accessed in a variety of ways, some of which may bypass the conventional user interface. Fortunately, the new Key Exists validation rule makes it easy to validate foreign key attributes, making quick work of what is normally a programming chore.