Use of Date with ADF

Date creates many confusion & bugs in our applications, some of which are only found when Day Light Savings time changes. :)

There is fundamental issue with how we talk about Date. For example, my date is in Central Time or for this Location my Date is in Eastern Time. As we all know, Date is milliseconds representing GMT time & String value we see in Debugger or Logs is just String representation of Date with respect to some TimeZone.

Here is what i recommend for Date usage with ADF, some of which can very well apply to other frameworks as well.

1. Don't offset date value for Persistence

JDBC driver will transform value of Date is Server's Default TimeZone for storing in Table Column. At times, we try to offset value of Date, so that when JDBC Driver creates String representation using Server's Default TimeZone, it looks like GMT for example. This is clever, but not a good idea.

This approach can cause issues with Queries. It will also not represent values correctly on screen components. You can workaround these issues, but that's extra work that can be avoided, by accepting the fact that Date will be stored in Server's Default TimeZone.

2. Do not specify Date Format on Control Hints for Entity or View Object attributes

ADF does a good job of providing Control Hints that can be set on Business Components, but in this case I would recommend not setting any Format for Date on Entity and View Object. I have seen issues with Control Hints related to Date Format and more importantly it makes sense to control this based on User's Preferences / Locale.

3. Create Session Scope variables for TimeZone & Date Format

Using Phase Listener, create Session Scope values for TimeZone and various Date & Time formats. You can read this values from User's Preference or derive it using any other data store.

These can be used in UI pages with af:convertDateTime as shown below.

 

4. Specify TimeZone in trinidad-config.xml

If you set value of time-zone in trinidad-config.xml, it will apply to all Date components for display and input processing.

5. Specify Pattern on af:date Specify different TimeZone if necessary on af:date

If you want to display particular Date value in a different TimeZone, you can indicate that on af:convertDateTime. For example, Delivery Date would make sense to be displayed in TimeZone of Delivery Location.

af:poll not working

ADF Faces provides poll component, it's description & sample use cases are documented on Tag Documentation as shown below.

The poll component delivers PollEvents to the server at fixed intervals. This can be used either for steady updates, or to deliver a heartbeat to keep a user logged in, or to warn a user about to be logged out (for some examples).

One classic use of Poll component would be to keep User Session active as long as browser window is open. In this case, you will set Poll Interval (interval) and dummy pollListener. Poll Listener can be empty method, it does not have to do anything. Poll Interval should be less than HTTP Session Timeout. HTTP Session Timeout is setup in web.xml.

Such use of Poll component fails to keep User Session active, after upgrading from 11.1.1.3. This is due to new attribute timeout for af:poll, value for which defaults to 10 minutes (This property is added with 11.1.1.4). So if user does not perform any activity on Keyboard or Mouse for 10 minutes, Poll component will stop delivering any Poll Events. If you are using af:poll to keep User Session (by sending regular heartbeat) active, add timeout property to af:poll with very high value to avoid stopping Poll Events.

How to define List of Values for View Object attribute

This is very powerful feature of ADF and it often goes unnoticed. You can define a List of Values for View Object attribute including component types that you want to use by default. Once this setup is done, when you Drop View Object on your page, it will create List components instead of simple text box.

Let's define Department List of Values for "DepartmentId" attribute of EmployeeVO. We have "EmployeeVO" (Default VO for Employee table) and "DeparmentsLOVVO" (has Id & Name for all Deparments).

First open EmployeeVO and Select DepartmentId attribute.

Expand List of Values:DepartmentId and click Green Plus icon. You will see "Create List of Values" dialog like one shown below. 

This is not very straightforward User Interface. Now you can select where your List Data is coming from in "List Data Source:", if you don't have one, click Green Plus icon to create one, see screen shot below.

Make sure that you name your view accessor appropriately. See i am using "VA" suffix.

Select "List Attribute" now. This is the value from your List Data Source that will be stored in your View Object attribute when User performs selection on UI.

You can use different value to display on your List component than what is being stored in your Attribute. This is done from UI Hints tab.

You are almost done. Go to EmployeeVO's View Accessor tab. Select your View Accessor and examine "Row Level Bind Values" property. If Rows in your EmployeeVO can use different Department List than this value should be true. (blank also means true). Easiest way to figure this out is if you have Bind Parameters on your List View Object (DepartmentLOVVO) and that is controlled by another attribute in your View Object (EmployeeVO). For example, if your View Object attribute is State and it's list changes based on Country attribute in that same View Object.

You must set this value to "false", if list is static for all Rows in your View Object, Otherwise you will see Memory Leak and Performance issues.

"Row Level Bind Values" is sometimes cleared by JDeveloper, which can lead to issues. This is something you want to create Audit Rules to make sure that your Build Process catches it. 

Define Primary Keys for all View and Entity Objects

When working with ADF, it is best to AVOID ISSUES by doing the right thing. Now that is broad statement, but i will try to post my learning's on this Blog.

Each ADF View & Entity Objects must have Primary Key.

ADF Business Components will generally have Primary Key defined, when they are generated using "Business Components from Tables" wizard. But in other cases when you have Read Only or Transient View Objects, they will not have Primary Key by default.

For example, see following steps to create List of Values (SQL based) View Object.

Note that DepartmentId is not selected as Primary Key. Select "Key Attribute" check box for all attributes that are part of Primary Key for this particular View Object.

Now you can see DepartmentId is selected as Primary Key.

ADF uses Primary Key for selection process, so if you did not have proper primary key, you will see weird behavior in Table Selection.

Use Non Schema User for ADF Business Components

ADF Model project is configured with Database Connection to generate Business Components from Tables and/or Views. Generated objects are Not Qualified with Schema name if you use Schema User for Connection Configuration. This can cause failures like "Table or View does not exist.", when application executes with a Different User. You can always resolve such errors by creating Synonyms. 

You have two options:

1. Use Non Schema User for JDeveloper Connection Configuration & no additional work needed when Sharing Code with other Applications.
2. Use Schema User for JDeveloper Connection Configuration. You will have to create Public Synonyms.

I recommend Option #1 as it is very simple and use of Option #2 can lead to confusion due to use of Synonyms. And this only applies to Code Generation, if you write SQL, you should implement similar option. 

Option 1 : Using Non Schema User for Database Connection

Option 2 : Using Schema User for Database Connection