In using the Repository design pattern, you can hide the details of how the data is eventually stored or retrieved to and from the data store. This data store can be a database, an xml file, etc.

Design patterns provide proven solutions to real world problems faced in software designs. The Repository pattern is used to decouple the business logic and the data access layers in your application.

Decouple with an Interface and the Repository Pattern A great way to separate the UsernameExists() method from the database-access code is to introduce an interface and apply the Repository pattern.