Implement canApprove() method in purchasing record Status Handlers

When implementing workflow for purchasing records (PR, PO, Invoice) it would be very useful to have a single method that contained all of the logic for verifying that the record is ready for approval. In some record types in Maximo, there is a canApprove() method in the record's Status Handler class that provides this ability.

For purchasing records, we've found that the Purchase Requisition (PR) does have a canApprove() method, but not all of the logic to validate the approval is contained in that method. For example, testing the validity of work orders on each PR Line is contained in the approve() method itself on the Status Handler. Invoices, however, do not have a canApprove() method in the Status Handler. There is a validateForApproval() method on the Invoice class, but again it does not contain all of the logic. Some additional checks are performed in the approve() method itself.

This becomes important when we involve workflow in the approval of these records. A standard workflow involves users preparing these records for approval and routing them to groups or individuals for approval. The final step of the workflow typically involves changing the status of the record to approved. It's frustrating for users who are the final step in the workflow to see an error message that the purchase requisition contains an invalid work order. They often think that this should have been caught much earlier in the process. Without the canApprove() method in the Status Handler containing *all* of the approval logic, the approval rules would need to be repeated in the workflow itself. Duplicating this logic is dangerous as these rules change with Maximo updates.