Apps To Fusion

In one of my old articles on OA Framework extension, I briefly mentioned about Nested Application modules. Today I will explain how Nested Application module can be used. Nested AM is an application module which is under the scope of root application module. Root application module is the AM attached to top region of the page during design time. It maintains the session state and retention level for requests between client and server.

Root AM can contain one or more nested AMs which can themselves nest children to any arbitrary level. In this scenario, the root AM has access to all the data/objects held by its children, and all children participate in the same transaction established by the root.

Design-Time

Suppose you have two application modules XxRootAM and XxNestedAM in your project. To make XxNestedAM nested to XxRootAM, you reference XxNestedAM in Application Module section of XxrootAM Editor. Below screenshot shows editor and how XxrootAM.xml is added with AppModuleUsage tag to reference XxNestedAM.

Run-Time

You use createApplicationModule() method in oracle.jbo.ApplicationModule Interface, to create an instance of application module on another application module. For the above example,
assuming ram is instance of XxRootAM, below command creates instance nam for XxNestedAM.

OAApplicationModule nam = (OAApplicationModule)ram.createApplicationModule("XxNestedAM", "xxa2f.oracle.apps.icx.icatalog.shopping.server.XxNestedAM");

You have to give full-qualified name of application module as second parameter. You can then access view objects attached to root application module, in nested application module. Suppose XxRootAM has view object XxVO, you can get instance of it in XxNestedAM using

ViewObject vo = nam.findViewObject("XXVO");

Note that XxNestedAM should be created declaratively before it can be nested using createApplicationModule() in run-time.


Why use nested application module?
Nested application module promotes reusablility and modularizing business logic into smaller and specific business components. It helps to prevent root application module in growing bigger and become nightmare for maintenance and concurrent development. Starting with release 11.5.10, nested application modules are instantiated on an "as needed" basis (in previous releases, BC4J instantiated all the nested application modules when the containing application module was created). For example, if you do a findApplicationModule , BC4J will instantiate the object. If a nested application module is never accessed, it is not created.

More importantly than usual, you can use nested application module to put custom business logic in root application module for seeded pages. It is not advisable to extend root application module. You can still get away with extending root AM until your seeded page doesn't have LOV fields. If page has LOV fields, root AM extension will cause session time out when clicked on LOV. The error looks similar to

"Error: Cannot Display Page
You cannot complete this task because one of the following events caused a loss of page data:
Your login session has expired.
A system failure has occurred. "

I was stuck up with the same error when I extended root AM in the Part-2 article of Custom Defaulting and Validation in iProcurment. So solution for root AM extension is to use nested application module. They come really handy in such scenarios.

Give me an example?
In iProcurement, I will add custom logic to print "Requisition Header Id" in console when "Add to Cart" button is pressed during requisition creation. Some details of 'About this Page' for Non-Catalog Request page.

Page Name: NonCatalogRequestPG
Controller: NonCatalogRequestCO
AM: RequisitionAM

To implement above requirement, I will create custom application module and make it nested to RequisitionAM in Controller. Then I will create printReqHeaderId() method to access PoRequisitionHeadersVO in custom application module and print Requisition Header Id in console.

Steps to use nested application module

• Create application module XxNestedAM in JDeveloper.
• Create a method printReqHeaderId in XxNestedAM to get instance of PoRequisitionHeadersVO via root application module. Use getter method to print requisition header id in console.

• Create extension NonCatalogRequestCO controller by naming it as xxNonCatalogRequestCO. In processFormRequest() method for AddToCart event, use createApplicationModule() to create instance of XxNestedAM and call method in nested application module using invokeMethod() method.

• Personalize NonCatalogRequestPG page to provide extended Controller XxNonCatalogRequestCO as controller.
  
• Run NonCatalogRequestPG in JDeveloper. Enter details in Non-Catalog Request page and hit Add to Cart button. This prints requisition header id in console output in JDeveloper.

This demonstrates how nested application module can be used to add custom business logic in seeded OA Framework pages.

Any other approach?

You can create a custom region say xxCustomRN with application module XxNestedAM and attach the region using OAF Personalization. So the application module XxNestedAM becomes nested to root application module via region. This involves more steps as you have to load custom region definition into MDS repository using XMLImporter utility and create flexible layout to attach custom RN to seeded page. I'll create my next article on this topic.

Update: I've implemented alternate approach in the article How to extend root AM using nested AM. I did not seem bad as I expected.

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