Using T4 templates to generate ViewModels

Question

In my mind this sounds like a superb idea. Using the EnvDTE would make this possible too, so why isn't there more examples on this available?

Maybe I'm missing an disadvantage of doing this...?

Any pointer to good T4 and EnvDTE resources would be great. :)

Answer 1

You probably don't see it around much because it's actually quite difficult to implement well. I've been using T4 to generate model classes from WCF DTOs for use in an WinForms MVP variant for a while now, and it took quite some time to get it working right.

Using a class as a "data" source for a template is pretty difficult in-and-of itself. You'll need to choose between using reflection (or a similar API) to read compiled IL or CodeDom to read the source code. If you choose to work with compiled assemblies, you'll need to contend with problems like file locking and loading referenced assemblies. If you choose to work with source code, you'll need to deal with potential uncompilable code.

Once you've made that decision, copying properties will be the most trivial thing you'll need to do. You'll also need to make decisions about which interfaces and attributes (if any) on the source class should be reimplemented/copied to the generated class. Depending on how you're implementing things like validation, this can raise all sorts of little, picky problems. There's are also a lot of fun decisions to make around how to handle inheritance hierarchies and references to other model classes.

All of the above is addressable, but a one-size-fits-all approach would be pretty hard to implement. Returning to the "example" part of your question, there's also the potential issue of doing quite so much work without getting paid for it. I'd love to be able to share the T4 I created for model generation, but it belongs to my employer, and I have better things to do with my spare time than re-implement the approach for posting on the web...

Answer 2

Using a class as a "data" source for a template is pretty difficult

This is wrong. Look at asp mvc 3 scaffolding. http://blog.stevensanderson.com/2011/01/13/scaffold-your-aspnet-mvc-3-project-with-the-mvcscaffolding-package/