Applies to Silverlight 4, 5
Validation of your data before persisting it is a requirement for almost every application. By using validation on your Entities, you make sure that no invalid data is persisted to your data store. With WCF RIA Services, there are various ways to do validation, each tailored to a specific scenario.
In this recipe, you'll learn how to validate data in which the validator should execute different code on server versus client, which is typically used when you want direct client-side feedback for cases where the validation logic has to execute a call to your server. A "username must be unique" validator is a very common scenario for such a validator.