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Unity 3.0 and Enterprise Library 6: Attribute based Policy Injection

For some time, Microsoft Unity supports the concept of Interception. It allows you to inject cross cutting concerns into your code by intercepting method calls and giving you the opportunity to execute some extra code before and after the call.

One of the nice features is that it integrates well with the Microsoft Patterns and Practices Enterprise Library Application Blocks(pfew, what a long name). So you can easily add for example caching or exception handling to your application without having to write the same code over and over again.

Until Enterprise Library 5.0 this was all encapsulated in a separate application block, the Policy Injection application block. Starting from Enterprise Library 6 this block is gone, although the same functionality should still be available inside the Unity.Interception DLL.

When upgrading to Enterprise Library 6.0, I was able to recreate most scenario’s by using this DLL. The only thing I had some trouble with finding out is how to combine Attribute based interception(where you indicate the interception calls by adding attributes on top of your methods) and existing objects. I found a lot of examples where the interception was applied when creating an object through the IoC container, but none when you have an existing object and want to apply interception techniques.

So for anyone who struggled with the same issue, here is the code I used to get this scenario working:

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