I'm using AutoMapper to map domain entities to view models in an Asp.Net MVC app. I register these mapping classes in Castle Windsor so they are available to the controller thru ctor dependency injection. These mapping classes has a virtual CreateMap method where I can override AutoMapper's mapping, telling it how to map fields from the entity to the view model, which fields to ignore, pointing to methods that transforms the data, etc. All of this is working well; big kudos to the people behind AutoMapper!
So far I've been registering the mapping classes with a Singleton lifestyle in Windsor, but one of them needs to use the IAuthorizationRepository from Rhino.Security which needs to have its components registered as Transient. This forces me to register the mapping classes also as transient, because a singleton mapping class holding a reference to a transient IAuthorizationRepository causes problems the second time the mapper is used (i.e., ISession is already closed errors).
Is it a waste of resources to register all of these mapping classes with a Transient lifestyle, which will cause the mapping class to be instantiated and the CreateMap method to run each time the system wants to map a domain entity to a view model?
Or should I try to find a way to separate the IAuthorizationRepository from the mapping class so I can keep the mapping classes as Singletons?
Thanks Dan