Question: What is Query
Collection in VO?
Answer:
Query Collection is
mainly used for caching the result of the executed query VO. A VO can have
multiple query collections depending on the rowsets.
Example: If we have 2
rowsets where DEPTID =10 and DEPTID=20. So the results of the executed VO with
these bind variables are stored in Query Collection.
Now we understood what are the other layers that are to be used before
hitting the data source? Now let us see how it will be executed with an
example:
Example: Let’s consider a
java code snippet where we execute a VO and retrieve the values
ViewObject vo =
ApplicationModule.findViewObject(“EmployeesVO”);
vo.executeQuery();
Row row = vo.first();
// gets the first row
Steps involved in executing this VO are as
follows:
1.
ADF client starts
interaction with the Application Module.
2.
ADF Client looks for the
requested View Object (EmployeesVO) instance in AM.
3.
Now before executing the
VO, it does as below:
a. Checks for relevant Query Collection
for Search Parameters (Bind Variables), if available uses the existing query
collection.
b. If not present created a new Query
Collection based on the Search Parameters.
4.
Once the QC is
initialized, the new Rowset instance calls the prepareRowSetQuery() on VO. This
is used for placing your customcode before Querycollection. (Eg: the Query for
the rowset with the bind variable).
5.
This is followed by executeQueryForCollection(),
which delegates the call for query collection instance and JDBC call for
particular Database.
6.
Now when a client tries
to get the first row in result set by calling first() , as the result set
retrieves the first row it displays the first row.
Question: How and When Groovy
Expression is used?
Answer: Groovy is interpreted at runtime; it
can be treated as metadata and customized. So, you could have an application
that has customized business rules in Groovy and those customizations stored in
Oracle ADF’s Metadata Services (MDS).
Oracle ADF provides a
number of different declarative points into which you can drop Groovy code:
1. Values for view and entity objects
attributes
2. Validation rules on entity object
attributes
3. Expressions for error messages
4. Values for view object bind variables
5. View object transient attribute
validation.
Examples:
1: For the transient
attribute AnnualSalary you could define a Groovy expression for the default to
be: Sal * 12
2: On the Sal attribute
you might want to define that a salesman must have a salary of less than 1000:
if (Job == "SALESMAN") {return newValue < 1000} else return true.
ADF Business Components
view objects also provide the ability to use Groovy expressions. As with entity
objects, view objects can support:
1. Referencing attributes in the same view
object
2. Referencing attributes in other view
objects
3. Transient attribute validation
4. Referencing methods in the Java class
that backs the view object
5.
Referencing
built in calls such as sum and min.
Question: What are the steps to
configure MDS? What are different kinds of MDS you configured? Which file hold
details of configured MDS?
Answer: To apply MDS to your application follow
this:
1. Pages should be
(.jspx) not (.jsp).
2. In your project
properties --> ADF View check on "Enable User Customizations" then
select "Across Sessions Using MDS".
3.Create a new class as
below. This class has two main functions:
- getName() which return
the folder name that hold all users changes.
- getValue() which return
the folder name for the login user. This folder should be unique for every
login user and will saved inside the getName() folder.
4. In Application Resources --> Descriptors --> ADF META-INF open
adf-config.xml.
5. In adf-config file go
to MDS Configurations and add your class
6. In adf-config file go to View tab and add all Tags.
7. Now you apply MDS to your application.
8. If you run your application in Integrated
Weblogic there will be no problem, you should only specify the path to store
the user changes (changes will stored in file system). You will find this path
in your Application properties --> Run --> MDS.
