Compared to AX 2009, assemblies in AX 2012 work a bit differently. One of the obvious differences is the introduction of visual studio projects. However, deploying the assemblies works differently, in our favor (of course!). There are a few things we need to keep in mind though, and definitely a few bad habits from AX 2009 to get rid of!
AX 2012 improves assembly deployment and referencing. For the client side of things, this means the assemblies no longer need to be copied to the client/bin folder. The development manuals for AX 2012 INCORRECTLY state that the assembly automatically gets downloaded by the client to the client bin folder. This is incorrect. The assemblies get downloaded to %USERPROFILE%\AppData\Local\Microsoft\Dynamics AX\VSAssemblies . The %USERPROFILE% by default on Windows 7 should be C:\Users\username so if your user name is DAXMUSINGS, the assemblies will be in C:\Users\DAXMUSINGS\AppData\Local\Microsoft\Dynamics AX\VSAssemblies . Make a correction in your 2012 development manual!
Since the assemblies are kept by user, that means in a multi-user environment such as terminal services or Citrix, there is no need for all users to log out (ie all client executables closed so no more assembly files are in use) before a new assembly can be deployed. First, you don't have to deploy, AX does it for you. Secondly, any time a user restarts AX, it will download the new assemblies where and if needed. It also means different users could have different versions of your code in use. This could happen traditionally with X++ as well, so it's always a good idea to schedule downtime to deploy new code, managed or otherwise.
So, when you build a Visual Studio project and click "deploy" in Visual Studio (or, in fact, if you just build the project and then restart your AX client), your AX client will, the next time it needs the assembly, detect a newer version of the assembly and copy it into the VSAssemblies directory. Also note that you can in fact build the project from the AOT. When you right-click/compile on a Visual Studio project, AX builds the project and thus a new assembly.
What happens on the server side? A similar thing, except here the assemblies are deployed to the server bin/VSAssemblies . By default, the AOS runs in 1 AppDomain which means you need to restart the AOS server to get the new assembly. But, in a developer environment you may be recompiling your assembly a lot, so to avoid having to restart your AOS constantly, hotswapping was enabled for the AOS. Check this MSDN page for more information. You should definitely never enable hotswapping in a production environment!
So, for anyone who has dealt with VS projects in previous versions, please don't copy assembly DLLs into your BIN directories. It will deploy automatically, refresh automatically, and load automatically. Also remember you don't have to explicitly add your Visual Studio's project as a reference in the AOT. The fact that it is an AOT VS project makes it available as an implicit reference anywhere in X++ . If you missed it previously, you may want to check out the managed code series for a look on how to create managed code projects.
Then there is the X++ compiled to IL. Those are assemblies too! Well, X++ is kept in the model store now. This includes the X++ source, the X++ p-code, and the X++ compiled IL. These compiled pieces are versioned, and the AOS will download newer versions of the X++ assemblies to it's server bin/XppIL folder, including the PDB files so you can debug that X++ running in the CLR using Visual Studio.