Friday, 29 July 2011

Task Flows: Sayonara automated nesting of Application Modules JDev

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Any readers of this post should also read the following follow-up post.

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In a previous blog post I discussed the concept of automated nesting of Application Modules (AMs) when using Bounded Task Flows (BTFs) with a combination of the transactional options Always Begin New Transaction, Always Use Existing Transaction and Use Existing Transaction if possible. The automated nesting of AMs is a very important feature as when you have a page made up of disparate regions containing task flows, and those regions have their own AMs, without the auto-nesting feature you end up with the page creating as many connections as there are independent region-AMs. Thus your application is less scalable, and architectural your application must be built in a different manner to avoid this issue in the first place.

This automated nesting of AMs is exhibited in the 11.1.1.X.0 series of JDeveloper and the ADF framework including JDev & Unfortunately, either by error or design this feature is gone in Having checked the JDev release notes and what's new notes, I can't see any mention of this change.

In turn I don't believe (please correct me if I'm wrong) there to be a section in the Fusion Guide that specifically talks about the interactions of the task flow transaction options and Application Module creation. The documentation talks about one or the other, not both in combination. This is somewhat of a frustrating documentation omission to me because it means Oracle can change the behaviour without being held accountable to any documentation stating how it was meant to work in the first place. All I have is a number of separate posts and discussions with Oracle Product Managers describing the behaviour which cannot be considered official.

In the rest of this post I'll demonstrate the changing behaviour between versions. It would be appreciated if any readers find errors in both the code, or even factual errors that you follow up with a comment on this blog please. I'm always wary of misleading others, I write my blog to inform and educate, not lead people down the garden path.

4 test applications

For this post you can download a single zip containing 4 different test applications to demonstrate the changing behaviour:

a) ByeByeAutoAMNestingJSPX111140
b) ByeByeAutoAMNestingJSPX111150
c) ByeByeAutoAMNestingJSPX111200
d) ByeByeAutoAMNestingFacelets111200

Why so many versions? My current client site is using, not, so I wanted to check there was consistent behaviour in the pre- releases. For this blog post I'll talk about the version, but the exactly same behaviour is demonstrated under

In addition I know that in the release because of the support for JSPX & Facelets, that the controllers have different implementations, so it is necessary to see if the issue is different between the two VDL implementations.

Besides the support for 4 different versions of JDev, and in the the different VDLs, each application is constructed in exactly the same fashion, using a near identical Model and ViewController setup. The following sections describe what has been setup in both these projects across all the example applications.

The Model project

Each application has exactly the same ADF BC setup connecting to Oracle's standard HR schema. The Model project in each application includes EOs and VOs that map to the employees and locaitons tables in the HR schema. The tables and the data they store are not consequential to this post, we simply need some Entity Objects (EOs) and View Objects (VOs) to expose through our Application Modules (AMs) to describe the AM nesting behaviour.

In the diagram above you can see the EOs and VOs. In addition I've defined 2 root level AMs EmployeesAppModule and LocationsAppModule. The EmployeesAppModule exposes the EmployeesView VO and the LocationsAppModule exposes the LocationsView.

To be clear, note I've defined these as separate root level AMs. So at the ADF BC level there is no nesting of the AMs defined. What we'll attempt to do is show the automatic nesting of AMs at the task flow level, or not, as the case might be.

In order to comprehend if the automated AM nesting is working at runtime, it's useful to add some logging to the ADF Business Components to show us such things as:

1) When our Application Modules are being created
2) If the AMs are created as root AMs or nested AMs

As such in each of the AMs we'll include the following logging code. The following example shows the EmployeesAppModuleImpl changes. Exactly the same would be written into the LocationsAppModuleImpl, with the exception of changing the log messages:
public class EmployeesAppModuleImpl extends ApplicationModuleImpl {
// Other generated methods

public static ADFLogger logger = ADFLogger.createADFLogger(EmployeesAppModuleImpl.class);

protected void create() {
if (isRoot())"EmployeesAppModuleImpl created as ROOT AM");
else"EmployeesAppModuleImpl created as NESTED AM under " + this.getRootApplicationModule().getName());

protected void prepareSession(Session session) {
if (isRoot())"EmployeesAppModuleImpl prepareSession() called as ROOT AM");
else"EmployeesAppModuleImpl prepareSession() called as NESTED AM under " + this.getRootApplicationModule().getName());
View Controller project

Each application has a near identical ViewController project with the same combination of task flows, pages & fragments. The only exception being the applications, where the Facelets application doesn't use JSPX pages or fragments, but rather Facelets equivalents. This section describes the commonalities across all applications.

Each application essentially is made up of 3 parts:

a) A Start page
b) A Bounded Task Flow (BTF) named ParentTaskFlow comprised of a single page ParentPage
c) A BTF named ChildTaskFlow comprised of a single fragment ChildFragment

Start Page

1) The start page is designed to call the ParentTaskFlow through a task flow call.


1) The ParentTaskFlow is set to Always Begin New Transaction and Isolated data control scope.

2) The ParentTaskFlow page contains an af:table showing data from the EmployeesView of the EmployeesAppModuleDataControl.

3) The ParentTaskFlow page also contains a region that embeds the ChildTaskFlow


1) The ChildTaskFlow is set to Use Existing Transaction if Possible and Shared data control scope

2) The ChildFragment fragment contains an af:table showing data from the LocationsView of the LocationsAppModuleDataControl

The behaviour under

When we run our application, and navigate from the Start Page to the ParentTaskFlow BTF showing the ParentPage, in the browser we see a page showing data from both the Employees VO and Locations VO. Of more interest this is what we see in the logs:
<EmployeesAppModuleImpl> <create> EmployeesAppModuleImpl created as ROOT AM
<EmployeesAppModuleImpl> <prepareSession> EmployeesAppModuleImpl prepareSession() called as ROOT AM
<EmployeesAppModuleImpl> <create> EmployeesAppModuleImpl created as NESTED AM under EmployeesAppModule
<LocationsAppModuleImpl> <create> LocationsAppModuleImpl created as NESTED AM under EmployeesAppModule
Based on my previous blog post on investigating and explaining the automated Application Module nesting feature in the 11.1.1.X.0 JDeveloper series, this is what I believe is occurring.

As the ParentTaskFlow is designed to start a new transaction, when the first binding in the page exercises the EmployeesAppModule via the associated Fata Control and View Object embedded in the table, ADF instantiates the AM as the root AM and attaches it to the Data Control Frame.

The Data Control Frame exists for chained BTFs who are joining transactions. So in this example the Employees AM is the first AM to join the Data Control Frame and it becomes the root AM. A little oddly we see the EmployeesAppModuleImpl then created again and nested under a root instance of itself. I'm not really sure why this occurs, but it might just be some sort of algorithmic consistency required for the Data Control Frame. Maybe readers might have something to share on this point?

It's worth noting the significance of a root AM unlike a nested AM, is only the root AM connects to the database and manages the transactions through commits and rollbacks. Nested AMs delegate these responsibilities back to the root AM. This is why we can see the prepareSession() call for the EmployeesAppModule.

When the page processing gets to the bindings associated with the ChildTaskFlow, within the fragment of the ChildTaskFlow it discovers the LocationsAppModule via the associated Data Control and View Object embedded in the table. Now we must remember that the ChildTaskFlow has the Use Existing Transaction if Possible and Shared data control scope options set. From the Fusion Guide this transaction option says:

"Use Existing Transaction if possible - When called, the bounded task flow either participates in an existing transaction if one exists, or starts a new transaction upon entry of the bounded task flow if one doesn't exist."

In order for the BTF to be part of the same transaction, it must use the same database connection too. As such regardless in the ADF Business Components where we defined the two separate Application Modules as root AMs (which by definition implies they have separate transactions & database connections), it's expected the task flow transaction options overrides this and forces the second AM to "nest" AM under the first AM as it wants to "participate in the existing transaction if it exists."

So to be clear, this is the exact behaviour we see in the logs of our 11.1.1.X.0 JDeveloper series of applications. The end result is our application takes 1 connection out with the database rather than 2.

The behaviour under

Under JDeveloper regardless if we run the JSPX or Facelets application, with exactly the same combination of task flow elements and transaction options, this is what we see in the log:
<EmployeesAppModuleImpl> <create> EmployeesAppModuleImpl created as ROOT AM
<EmployeesAppModuleImpl> <prepareSession> EmployeesAppModuleImpl prepareSession() called as ROOT AM
<LocationsAppModuleImpl> <create> LocationsAppModuleImpl created as ROOT AM
<LocationsAppModuleImpl> <prepareSession> LocationsAppModuleImpl prepareSession() called as ROOT AM
As such regardless that the Oracle task flow documentation for the latest release says that the second task flow with the Use Existing Transaction if Possible option should join the transaction of the calling BTF, it doesn't. As can see from the logs both AMs are now treated as root and are preparing their own session/connection with the database.

The effect of this is our application now uses 2 connections rather than 1, and in turn the BTF transaction options don't appear to be working as prescribed.

Is it just a case of philosophy?

Maybe this is just a case of philosophy? Prior to JDev the ADFc controller (who implements the task flows) was the winner in how the underlying ADF BC Application Modules were created and nested. Maybe in Oracle has decided that no, in fact the ADFm model layer should control its own destiny?

Who knows – I don't see any documentation in the release notes or what's new notes to tell me this has changed. The task flow transaction option documentation is all I have. As such if you've relied on this feature, your architecture is built on this feature as we have, we're now in a position we can't upgrade our application to without major rework.

To get clarification from Oracle I'll lodge an SR and will keep the blog up to date on any information discovered.

-- Post edit --

Any readers of this post should also read the following follow-up post.

-- End post edit --


Unknown said...

Just a guess but could it be your 11.1.2 setup is using JDBC datasources with global transactions either through XA drivers or non-XA drivers with global txn enabled where WLS will handle two phase commit. That might give 11.1.2 another way to share a transaction across two db sessions. Still a shame it is opening two db sessions though as to resource consumption at the db server

Haven't tested any of this but just a long shot

Chris Muir said...

Hi Wilfred

In fact the demos are all using JDBC URLs, but I think you might be on the right track. I'm hoping there is just some silly rule that has been introduced with the AMs' connections, which when satisfied will bring back the old behaviour.

I suspect if U had the 11.1.2 ADF source code & experience in understanding it I could determine this myself. Regardless I hope Oracle doesn't assume that fact, that we're now required to understand the source code to understand the feature set, because then we all need to be Java champions to make good use of ADF.

Friday night grumble grumble on my part. I'll lodge the SR early next week & see what response we get.

Thanks for your follow up reply.


Chris Muir said...

Any readers of this post should also read the following follow-up post.