How to invoke various Child processes from a Parent process with out a call activity?

Camunda 7 Topics Discussion & Questions
1

Hi All, I have a parent process - ProcessA from which I would like to initiate various Child processes - ChildA, ChildB, ChildC… I would like to know how to accomplish this with out using call activities?

2

Is there any specific reason you want to avoid Call Activities?

The first alternative that comes to mind would be a multi-instance send task which would send a message to trigger the child process. But in this cases you should be aware that there’s no parent child relationship as far as the engine in concerned

3

@startrek You can use message start events for starting child processes without call activity. As @Niall suggested you can use multi instance send task if you want to start multiple processes in parallel/sequential.

If it’s a choice between choosing the child processes to initiate, then refer the below example:

Deploy this bpmn file and start the parent process from tasklist: MessageStartEventTest.bpmn (9.8 KB)

Parent Process:

image
image3576×1542 393 KB

Child Process A:

image
image3582×1400 354 KB

Here’s a delegation code for correlating child process’s message start events:

@Slf4j
@Component
public class ChildProcessInvocationDelegate implements JavaDelegate {

	@Autowired
	private RuntimeService runtimeService;

	@Override
	public void execute(DelegateExecution execution) throws Exception {
		log.info("Child process {} will be initiated...", execution.getVariable("childProcess"));
		ProcessInstance processInstance = runtimeService
				.createMessageCorrelation((String) execution.getVariable("childProcess"))
				.setVariable("referenceKey", execution.getVariable("referenceKey")).correlateStartMessage();
		runtimeService.setVariable(execution.getId(), "childProcessInstance_Id", processInstance.getId());
	}

}
1 Like
4

Thanks @Niall and @aravindhrs for your suggestions. I am trying to achieve this as below:

ProcessA:

pc
pc1174×526 36.3 KB

ProcessB:

dc
dc1103×446 21.4 KB

  1. From ProcessA, I should be able to initiate ProcessB and ProcessC at any point.
  2. On ProcessA, if I invoke a message to initiate ProcessB, I am trying to catch using the Message Catch Event, which should transfer the flow to the Message Throw Event
  3. In the Message Throw Event, I am sending a message i.e startProcessB, which is not working.

Am I doing something wrong here?

5

To be more precise, I want to start a child process from the parent by sending a message without the usage of Java delegate code. Not sure if this can be accomplished with Message Throw event or a Message Send Task as either of them didn’t work as desired

6

Hi @startrek,

you have to provide an implementation in your message throw event of process A to send the message.

You can use the code from @aravindhrs for this.

The message name that you defined in the process model is not used by the process engine.

Hope this helps, Ingo

7

Thanks @Ingo_Richtsmeier , so this can be achieved only through an implementation such as a Java delegate? I was thinking if this can be done using a much simpler way using an expression/delegate expression may be.

8

Hi @startrek,

a Java delegate is most basic implementation.

Of course you can abstract your code and choose a more loosly coupled way to bind it to the service task.

An expression like

${execution.getProcessEngineServices().getRuntimeService().createMessageCorrelation("myMessage").setVariable("name", "value").processInstanceBusinessKey("myBsuinessKey").correlate();

could do the same and trigger process B.

There are many possibilties to reach your goal, and the main message:
You need some code to send the message.

Hope this helps, Ingo

1 Like
10

Thank you @Ingo_Richtsmeier @Niall @aravindhrs ! Guess my assumptions are wrong then. I assumed that as the name indicates, one can directly send/throw a message through a Message Throw Event by specifying the message property on that event which would invoke a Message Start Event.

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