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Dynamics 365 for finance & operation/AX 7- Chain of command

Dynamics 365 for finance & operation/AX 7- Chain of command

In past couple of releases and updates from Microsoft, Dynamics 365 for finance & operation aka AX7 came up with a lot more new Extension feature. Current version came with a lot of hard sealed version and few are soft sealed. Hard seal packages will not allow a developer to make any changes in the existing code but still this flexibility is there with the soft sealed packages. But it's best practices to avoid changes or modifications in the existing piece of code because you never know the next version will come with all hard sealed packages.

So there are multiple extension features that we are already aware of like delegates, events and pre & post event handlers. As part of update 9, Microsoft has given one more extension possibility which is Chain of command. Now Pre & Post functionality can be used in Extensions in more easier way. And it also provides developers flexibility to work with Protected methods and variables directly in the Extension class.

Now lets understand how Chain of commands works with the following example:

Suppose we have a standard class "TestCOC" in which one method we need some customization.

Class TestCOC
{
        public void run()
        {
                 This.testMethod();
        }
        protected void testMethod()
        {
                info(“Inside main testCOC”);
        }
}


Now there is a child class which extends TestCOC i.e. ChildTestCOC.



class ChildTestCOC extends TestCOC
{
protected void testMethod ()
{
                    info("child class before super");
                    super();
                    info("child class after super");
}
}

Lets say you want to write some custom code in child class’ testMethod(). How you’ll achieve it using Chain of command?

First you need to create an extension class for your child class and have to create same method with exact signature.

[ExtensionOf(classStr(ChildTestCOC))]
Final class ChildTestCOC_Extension
{
protected void testMethod ()
{
          //Insert before actual method execution
                    info("Custom logic before super()");
                   
                   next testMethod();

                   //insert logic after actual method execution
                    info("Custom logic before super()");
}
}

The method we added here is the new chain of command definition. We use exactly the same notation as the original method we are extending and add a mandatory “next” keyword to the call which will wrap our extension code around the extended method. This next keyword separates the pre and post parts of our extension and mandatory to be called inside the chain of command method. Next call cannot be placed in any kind of program block like if() block or while block. When you call next(), it checks for other extensions in the queue and runs them in random order, lastly running the base code.

Not only methods, Chain of commands also shares the access for protected variables from your base code/class.

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