Retaining Association accessor

In BC4J its easy to create a parent-child relationships between entity objects. This is done using the entity association objects.

Every time when an entity association accessor is accessed, ADF bc by default creates a new RowSet object containing all the child rows associated to the current parent entity object. This does not mean that an sql query will be re-executed to fetch all the child rows . This only means that a new instance of a RowSet object will be created with its default iterator reset to the "slot" before the first row. To force the row set to refresh its rows from the database, executeQuery() method has to be called.

Since there is a small amount of overhead associated with creating the row set, if your code makes numerous calls to the same association accessor attributes, you can consider enabling the association accessor row set retention for the source entity object in the association. You can enable retention of the association accessor row set using the overview editor for the entity object that is the source for the association accessor. Select Retain Association Accessor Row Set in the Tuning section of the General page of the overview editor for the entity object.

When this feature is enabled for an entity object, since the association accessor row set is not recreated each time, the current row of the RowSet object is also retained as a side-effect. This means that inorder to reset the currency of the row set , the "reset" method has to be called on the row set object. A failure to call reset() each time before the rowset is iterated, can result in hard-to-detect error in your application.

So the best way to iterate through the rows is to have code as follows..

RowSet rs=.....

rs.reset();

while(rs.hasNext()){
Row row=rs.next();
}

So irrespective of whether the association accessor is retained or not, this code will help to scroll through all the rows of the row set...

The method "rs.hasNext()" might fire an sql query , if its the first time the row set is being called. So only the first time a rowset is being scrolled, the framework fires an SQL query and populates the row set..In other cases, the method "hasNext()" will just check if there is any row in the entity cache or not....

If you always want to access all the rows that have been created in the middle tier as well as all the rows from the database use the following piece of code..

RowSet rs=.....

rs.executeQuery();

while(rs.hasNext()){
Row row=rs.next();
}

This code works irrespecitive of whether the association accessors are retained or not...This code will fetch all the new rows from the middle tier and all the rows (even the new rows commited to the database from backend ) from the database...

Programmatically setting the association accessor retention

To programmatically set the association accessor retention do the following..

Generate the Entity Collection class...In this class, there should be a method like "init()"...In this method, after the line "super.init();" call the method "setAssociationAccessorRetained(true)", by passing "true" as parameter...