Implementing change pointers, WebSphere Adapter for SAP Software

A change pointer uses change documents and is one of the more challenging event detection mechanisms to implement. The SAP Business Object Repository (BOR) is used as well as Application Link Enabled (ALE) technology. A change document always refers to a business document object having at least one database table assigned to it. If the data element in a table is marked as requiring a change document and the table is assigned to a business document object, then a change in value of the field defined by the data element generates a change document. The changes are captured in tables CDHDR and CDPOS and are used for event detection.

About this task

Note: This procedure is for the Advanced event processing interface only. If you are not using the Advanced event processing interface, skip this procedure.

To implement change pointer for event detection:

Procedure

Activate the global Change pointers flag in transaction BD61.
Change the SAP function module CHANGE_POINTERS_CREATE to include the function module call to /CWLD/EVENT_FROM_CHANGE_POINTR.
Determine which verbs to support: Create, Update, or Delete.
Check if the SAP business process (transaction) utilizes change documents:
- In the Environment menu for the transaction, does a Change function exist? How about when you click Go To, and then click Statistics?
- If you change data in the transaction, is there a new entry in table CDHDR that reflects the change?
- In the database tables associated with a transaction, do any of the data elements have the Change Document flag set?
If the answer is Yes to any of these questions, the transaction uses change documents.
1. Determine if the data elements that set the Change Document flag capture all of the information needed to detect an event. Changing the Change Document flag is not recommended because it changes an SAP-delivered object.
2. Determine the business object key for the transaction. The business object key must be unique so that the business object can be retrieved from the database. A composite key may be required. This is normally table/field CDHDR-OBJECTID.
3. Determine the criteria for detecting an event. Use table/field CDHDR-OBJECTCLAS as the main differentiator. CDPOS-TABNAME may also be used to detect the event.
4. Update function module /CWLD/EVENT_FROM_CHANGE_POINTR with the logic to detect the event.

Example

The following example of an SAP sales quote can be used to implement an event trigger using change pointer:

Update is determined to be the supported verb. Investigating the sales quote create transaction shows that the Create verb is not detected through this mechanism.
When performing the checks of the business for sales quote:
- The Change function is available from the Environment menu in transaction VA22.
- Making a change to a sales quote results in a new entry in table CDHDR.
- Looking at table VBAP, the field ZMENG has the Change Document flag set.
No evaluation of data elements was done for this example.
The sales quote number is determined to be the unique key in CDHDR-OBJECTID.
CDHDR-OBJECTCLAS has a value of VERKBELEG, which is the main differentiator. Only sales quotes should be picked up. The code checks the TCODE field in the header table, but a proper lookup should be done in the VBAK table.

The following sample code is added to /CWLD/EVENT_FROM_CHANGE_POINTR:

when 'VERKBELEG'.  	
	data: skey like /cwld/log_header-obj_key,  	
	s_event like swetypecou-event,  	
	r_genrectype like swetypecou-rectype,  	
	r_rectype like swetypecou-rectype,  	
	t_event_container like swcont occurs 1 with header line.   

" Quick check. Should check document category (VBTYP) in VBAK.  
check header-tcode = 'VA22'.   

" Event detection has started  
perform log_create using c_log_normal c_blank c_event_from_change_pointer c_blank.   

" Set the primary key  
skey = header-objectid.   

" Set the verb  
s_event = c_update_event.   

" Log adding the event to the queue  
perform log_update using c_information_log text-i44  			
	'SAP4_SalesQuote' s_event skey.   

" Event detection has finished.  
perform log_update using c_finished_log c_blank  			
	c_blank c_blank c_blank.   

call function '/CWLD/ADD_TO_QUEUE_AEP'  	
	exporting  		
		obj_name = 'SAP4_SalesQuote'  		
		objkey = skey  		
		event = s_event  		
		generic_rectype = r_genrectype  	
	importing  		
		rectype = r_rectype  	
	tables  		
		event_container = t_event_container  	
	exceptions  		
		others = 1.

What to do next

Configure the adapter for Advanced event processing.