Dependency Injection ,Repository Pattern

There isn't any single rule for good or bad. All approaches are bound with situation. You might have seen many old applications running on old technologies, generating good business. So depends on scenario you would decide what to use and where to use. This knowledge is mainy through experience...

 

About Dependency Injection(DI), in a high level DI decouples different layers of your application so that you can modify/develop them wihout impacting each other. This is contributing to unit testing and mocking them too, independently. DI separates the creation of a client's dependencies from the client's behavior. it's a broad area and can't put it all in here.