26.2 Updating a Deleted Flag Instead of Deleting Rows

For auditing purposes, once a row is added to a table, sometimes your requirements may demand that rows are never physically deleted from the table. Instead, when the end-user deletes the row in the user interface, the value of a DELETED column should be updated from "N" to "Y" to mark it as deleted. This section explains the two method overrides required to alter an entity object's default behavior to achieve this effect. The following sections assume you want to change the Product entity from the SRDemo application to behave in this way. They presume that you've altered the PRODUCTS table to have an additional DELETED column, and synchronized the Product entity with the database to add the corresponding Deleted attribute.

26.2.1 How to Update a Deleted Flag When a Row is Removed

To update a deleted flag when a row is removed, enable a custom Java class for your entity object and override the remove() method to set the deleted flag before calling the super.remove() method. Example 26-4 shows what this would look like in the ProductImpl class of the SRDemo application's Product entity object. It is important to set the attribute before calling super.remove() since an attempt to set the attribute of a deleted row will encounter the DeadEntityAccessException.

Example 26-4 Updating a Deleted Flag When a Product Entity Row is Removed

// In ProductImpl.java
public void remove() {
  setDeleted("Y");
  super.remove();
}

The row will still be removed from the row set, but it will have the value of its Deleted flag modified to "Y" in the entity cache. The second part of implementing this behavior involves forcing the entity to perform an UPDATE instead of an INSERT when it is asked to perform its DML operation. You need to implement both parts for a complete solution.

26.2.2 Forcing an Update DML Operation Instead of a Delete

To force an entity object to be updated instead of deleted, override the doDML() method and write code that conditionally changes the operation flag. When the operation flag equals DML_DELETE, your code will change it to DML_UPDATE instead. Example 26-5 shows what this would look like in the ProductImpl class of the SRDemo application's Product entity object.

Example 26-5 Forcing an Update DML Operation Instead of a Delete

// In ProductImpl.java
protected void doDML(int operation, TransactionEvent e) {   if (operation == DML_DELETE) {     operation = DML_UPDATE;   }   super.doDML(operation, e);  }

With this overridden doDML() method in place to complement the overridden remove() method described in the previous section, any attempt to remove a Product entity through any view object with a Product entity usage will update the DELETED column instead of physically deleting the row. Of course, in order to prevent "deleted" products from appearing in your view object query results, you will need to appropriately modify their WHERE clauses to include only products WHERE DELETED = 'N'.