What happens when a View Object is Executed ?

I am sure you would learn something new from this blog , thats the main intention of this blog 

What are View Objects : 

 

   View Objects are the  business components  that collect data from data source and the data can be modified/shape the data accordingly.

 

   Their are two types of View Objects :

One is Read-Only and the other is Updatable ViewObject which is based on Entity Object . 

 

 Lets us see the internal architectural understanding of View Object and what happens when we execute a query : 

 

     Internally before the view object hits the data source , it goes through few other stages which are as follows : 

 

   RowSets :  VO uses a special data structure known as RowSet to manage the collection of rows from a query on data source(Database). It has a default rowset or primary rowset ,So when ever for the first time if we execute the VO it first hits the default rowset.  

                    

Example : Lets us take a VO based on a query where it has a bind variable as DEPTID. So the query can have a bind vairable and each time you pass a value lets say DEPTID=10 

and again we pass DEPTID =20 . So each time you pass a variable it stores them in a rowset . If they already have a same rowset , it will consider the same rowset instead of creating new one . For example if DEPTID =10 is already their as rowset , it will consider the same instead of creating new one . 

 

  

Query Collection : 

   

   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 will it be executed with a example : 

 

 Example :  Lets 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 excuting 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 revelant Query Collection for Search Parameters (Bind Varibles ) ,                 If available uses the existing querycollection.

       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 .

 

What if the ViewObject is Based on Entity Object ?

 

  When the ViewObject is based on EO , an entity Instance will be created  and added to corresponding entity cache. 

 

Hope this helps …..