In my first two posts on models in AX (Part 1 and Part 2) I covered the deployment specific behaviors of .axmodel files - it should be apparent we introduced .axmodel files as a deployment replacement for AOD files. In the process we added some nice capabilities like a manifest and signing. The real benefit of models, and the ultimate reason we are adding this level of abstraction is because:
You can have as many models per layer as you want.
Let us examine this statement. In AX2009 a layer is the confinement unit of model elements. The layer is the unit of which you can export, deploy and delete model elements. (Here I'm deliberately ignoring the capabilities provided by XPO files, as these are suitable for development purposes only, and not deployment.) In AX6 this limitation has been removed, that means you can segment your layer into as many models as you like.
Here are a few examples where this could be useful in development scenarios:
Let's examine the statement a bit deeper. There are two ways of getting a model: Either you create one on your own, or you receive it from someone else. If you can have as many models as you want per layer, it also means:
You can deploy models from several sources into the same layer.
Here is an example: You are a customer and would like to install two ISV solutions that both are available in the BUS layer. In AX2009 you would have a tough choice to make: Either you picked your favorite solution and learned to live without the other one, or you invested in having the two solutions merged into one layer. This merge is technical challenging, and a costly affair once updates to either solution are being released. In AX6, however, you download the two models, and use AxUtil to import them. When a new version of either model is released, you simply use AxUtil to update the model.
This all sounds too good to be true, what is the downside? There is one limitation to what a model can contain:
An element can only be defined once per layer.
This means that two models containing a definition of the same element cannot be installed in the same layer. For example; if the two models both contain a class named: "MyClass" they will not be able to install side-by-side in the same layer. Model elements have two alternate keys, they are: [Type, Parent, ID] and [Type, Parent, Name]. Each layer can only contain elements that can uniquely be identified via the two alternate keys. In less technical terms, this means that two elements of same type under same parent (or without a parent) cannot co-exist if they have same name or same ID. For example: A table cannot have two fields with same name, or two fields with same ID. Another example: You cannot have two display menu items with the same name.
There are three ways you can be hit by this limitation:
So apparently we cannot guarantee that models can co-exist in the same layer - so what are the options when two models are in conflict? When you import a model that conflicts with an already imported model, you get three options:
For example; if two models ("ModelA" and "ModelB") are imported into the BUS layer, then "ModelA" is imported without any problems, and "ModelB" will be imported into two models: "ModelB" in the BUS layer, and "ModelB_Conflicts" in the BUP layer.
For example; If a model "ModelA" containing PatchA is already installed, and a new model "ModelB" containing PatchA+B is being installed then this is the right option. Later; if "ModelB" is being uninstalled, then "ModelA" is also automatically uninstalled.
Models enable a lot of highly desirable scenarios, one of the most important scenarios being that models from different sources - for example, two ISVs - can be installed in the same layer side-by-side. There are a few technical limitations; but the risk of conflicts is much reduced in AX6 and even when conflicts occur there is a less-expensive way to make the models co-exist.
More on models...
This post is a part of a series on models:
This posting is provided "AS IS" with no warranties, and confers no rights.