Add methods to tables through extension

When you extend the business logic that is related to a table, the general coding principles that help keep your code clean still apply. Therefore, you must eventually encapsulate actions in separate methods on the table. In Microsoft Dynamics AX 2012, you completed that task by adding the method directly on the table through overlayering. To complete the same task through extension, you use a different approach. Specifically, you create an augmentation class.

For example, a new field that is named MyInventLocationId was added to the InventTable table through extension. A data event handler was also created for the Inserting event, and you must implement the logic of filling the new field there. To encapsulate that action, you will create a new method on InventTable and name that method myDefaultInventLocationId.

You first create a new class in the extension model. This class will augment the InventTable table, and enable access to the table's fields and methods in a manner that is easy to read and understand. It's important that you choose the correct name for your augmentation class. This name must be unique across all types in all models that are deployed. For more information, see Naming guidelines for extensions.

[ExtensionOf(tableStr(InventTable))]
final class InventTableMy_Extension
{
    public void myDefaultInventLocationId()
    {
        // This would have partner specific logic to initialize the new field.
        this.MyInventLocationId = this.inventLocationId();
    }
}

You can now add new methods to the augmentation class. These methods will then appear in IntelliSense for variables of the InventTable type, just as if they were defined directly on the table. This behavior applies to both static methods and instance methods.

There are a few rules for augmentation classes:

• They must be final.
• They must be suffixed by _Extension.
• They must be decorated with the [ExtensionOf()] attribute.

Now you can use your new method, for example, from an event handler:

class InventTableMy_EventHandler
{
    [DataEventHandler(tableStr(InventTable), DataEventType::Inserting)]
    public static void InventTable_onInserting(Common sender, DataEventArgs e)
    {
        InventTable inventTable = sender as InventTable;
        // Call the method as if it was defined directly on InventTable.
        inventTable.myDefaultInventLocationId();
    }
}

Note

It is common for event handler classes to contain handlers for any number of events. However, it is not good practice to put event handlers in augmentation classes. Doing so makes the event handler methods available as methods on the augmented type. This is incorrect because the event handler is intended to be called through the event, not explicitly as a method on the type.