如何以编程方式重新下载应用内购买应用程序

I am able to implement in-App purchase successfully. I am also able to purchase a product through in - App purchase.I am storing purchase information in NSUserDefaluts.So if next time user tries to purchase same product again i am able to handle it locally.My problem is if a user deletes the application from the device,How do i handle the re-downloading of the application without charging for the same product again.I know that if an application has been deleted from the device having in App purchase it has to be downloaded again.Can anybody show a sample code for the same?I am able to implement in-App purchase successf