Overriding remove() to delete a parent entity in an association

In this recipe, we will present a technique that you can use in cases that you want to delete the parent entity in an association when the last child entity is deleted. An example of such a case would be to delete a department when the last department employee is deleted.

Getting ready

You will need access to the HR schema in your database.

How to do it...

  1. Start by creating a new Fusion Web Application (ADF) workspace called HRComponents.
  2. Create a database connection for the HR schema in the Application Resource section of the Application Navigator.
  3. Use the Business Components from Tables selection on the New Gallery dialog to create Business Components objects for the DEPARTMENTS and EMPLOYEES tables.
  4. Double-click on the EmpDeptFkAssoc association on the Application Navigator to bring up the Association editor, then click on the Relationship tab.
  5. Click on the Edit accessors button (the pen icon) in the Accessors section to bring up the Association Properties dialog.
  6. Change the Accessor Name in the Source Accessor section to EmployeeDepartment and click OK to continue.
  7. Generate custom Java implementation classes for both the Employee and Department entity objects.
  8. Open the EmployeeImpl custom Java implementation class for the Employee entity object and locate the remove() method.
  9. Replace the call to super.remove() with the following code: 
    // get the associated department
DepartmentImpl department = this.getEmployeeDepartment();
// get number of employees in the department
int numberOfEmployees = department.getDepartmentEmployees().getRowCount();
// check whether last employee in the department
if (numberOfEmployees == 1) {
  // delete the last employee
  super.remove();
  // delete the department as well
  department.remove();
}
else {
  // just delete the employee
  super.remove();
}

How it works...

If you followed the Overriding remove() to delete associated children entities recipe in this chapter, then steps 1 through 8 should look familiar. These are the basic steps to create the HRComponents workspace, along with the business components associated with the EMPLOYEES and DEPARTMENTS tables in the HR schema. These steps also create custom Java implementation classes for the Employee and Department entity objects and setup the EmpDeptFkAssoc association.

The code in remove() first gets the Department entity row by calling the accessor getEmployeeDepartment() method. Remember, this was the name of accessor—EmployeeDepartment—that we setup in step 6. getEmployeeDepartment() returns the custom DepartmentImpl that we setup in step 7. In order to determine the number of employees in the associated Department, we first get the Employee RowIterator by calling getDepartmentEmployees() on it, and then getRowCount() on the RowIterator. All that is done in the following statement:

int numberOfEmployees = department.getDepartmentEmployees().getRowCount();

Remember that we setup the name of the DepartmentEmployees accessor in step 6. Next, we checked for the number of employees in the associated department, and if there was only one employee—the one we are about to delete—we first deleted it by calling super.remove(). Then we deleted the department itself by calling department.remove(). If more than one employee was found for the specific department, we just delete the employee by calling super.remove(). This was done in the else part of the if statement.

There's more...

Note the implications of using getRowCount() versus getEstimatedRowCount() in your code when dealing with large result sets: getRowCount() will perform a database count query each time it is called to return the exact number of rows in the view object. On the other hand, getEstimatedRowCount() executes a database count query only once to fetch the view object row count to the middle layer. Then, it fetches the row count from the middle layer. The row count in the middle layer is adjusted as view object rows are added or deleted. This may not produce an accurate row count when multiple user sessions are manipulating the same view object at the same time. For more information on this topic, consult the section How to Count the Number of Rows in a Row Set in the Fusion Developer's Guide for Oracle Application Development Framework.

See also

  • Overriding remove() to delete associated children entities, in this chapter
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