WebSphere Business Integration Adapters: An Adapter Development and WebSphere Business Integration Solution

134 WebSphere Business Integration Adapters

Table 8-20 Method for releasing event-store resources

For example, if the event store is implemented as event tables in a database, the

pollForEvents() method might allocate SQL cursors to access these tables.

You can implement a cleanupResources() method to free these SQL cursors. At

the end of pollForEvents(), you can then call the cleanupResources() method

to free the memory that these cursors use.

8.5 Processing delete events

An application can support one of the following types of delete operations:

 Physical delete (data is physically deleted from the database).

 Logical delete (a status column in a database entity is set to an inactive or

invalid status, but the data is not deleted from the database).

It might be tempting to implement delete event processing in a manner that is

consistent with the application. For example, when an application entity is

deleted, a connector poll method for an application that supports physical deletes

might publish a business object with the Delete verb. A connector poll method for

an application that supports logical deletes might publish a business object with

the Update verb and the status value changed to inactive.

Problems can arise with this approach when a source application and a

destination application support different delete models. Suppose that the source

application supports logical delete and the destination application supports

physical delete. Assume that an enterprise is synchronizing between the source

and destination applications. If the source connector sends a change in status (in

other words, a delete event) as a business object with the Update verb, the

destination connector might be unable to determine that the business object

actually represents a delete event.

Therefore, event publishing must be designed so that source connectors for both

types of applications can publish delete events in such a way that destination

connectors can handle the events appropriately. The Delete verb in an event

notification business object should represent an event where data was deleted,

Java connector library class Method

CWConnectorEventStore cleanupResources()

Note: The CWConnectorEventStore class does not provide a default

implementation of the cleanupResources() method. To free event-store

resources, you must override the cleanupResources() method with a version

that releases the resources needed to access your event store.

Chapter 8. Asynchronous event processing and notification 135

whether the delete operation was a physical or logical delete. This ensures that

destination connectors will be correctly informed about a delete event.

8.5.1 Setting the verb in the event record

The event detection mechanism for both logical and physical delete connectors

should set the verb in the event record to Delete:

 For a physical delete connector, this is the standard implementation.

 For a connector whose application supports logical deletes, the event

detection mechanism must be designed to determine when update events

actually represent deletion of data.

In other words, it must differentiate update events for modified entities from

update events for logically deleted entities. For logically deleted entities, the

event detection mechanism should set the verb in the event record to Delete

even if the event in the application was an Update event that updated a status

column.

8.5.2 Setting the verb in the business object

The poll method for both logical and physical delete connectors should generate

a business object with the Delete verb:

 If the application supports logical deletes, the connector poll method retrieves

the delete event from the event store, creates an empty business object, sets

the key, sets the verb to Delete, and sends the business object to the Adapter

Framework.

For hierarchical business objects, the connector should not send deleted

children. The connector can constrain queries to not include entities with the

status of inactive, or child business objects with a status of inactive can be

removed in mapping.

 If the application supports physical deletes, the connector might not be able to

retrieve the application data. In this case, the connector poll method retrieves

the delete event from the event store, creates an empty business object, sets

the key values, sets the values of other attributes to the special Ignore value

(CxIgnore), sets the verb in the business object to Delete, and sends the

business object to the Adapter Framework.