Message Start Event doesn't start

BPMN & Modeling Discussion & Questions
1

Hi guys,

I’m currently building a workflow with 2 pools. I’d like to use Message Start Event to trigger the second pool tasks. I read through the example given in the modeller tutorial, but it seems the task in the second pool cannot start.

The workflow is shown below. I set the Message and Message Name attributes for the Message Start Event.

Then I deployed it into Camunda Engine. I started process in the first pool. And I claimed and completed the task. But it seems the Message Start Event doesn’t start when I completed the task.

There supposed to be an instance in the second pool , right ?

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I think I might miss some configuration for the Message Start Event, or I didn’t understand it in a correct way.

Any suggestions would be much much appreciated.

If I didn’t explain the issue clearly, please let me know

Thank you guys.

2

Hi @casparhpf

Welcome to the forum.
So the first thing to understand is that those message flows are simply visual indicators. They do not have any execution semantics and so adding them to your models doesn’t actually sent a message.
Sending a message requires you to write a script or some code which actually triggers it.
Also - for executable models you cannot send a message from a user task - you need a send task or a send event in order to send a message.

You could either send it using a JavaClass

       delegateExecution.getProcessEngineServices()
               .getRuntimeService()
               .createMessageCorrelation("MessageName")
               .correlate();

or similarly as part of a script.
To understand it better you can take a look at this video tutorial.

3

@casparhpf Refer this post and attached producer_consumer bpmn example.

producer_consumer.bpmn (5.8 KB)

4

Hi @Niall

Thank you very much for your super fast response.

I’ve watched your YouTube video before and it was quite clear. Since I’m not using Java to interact with Camunda Engine, I may have to reconsider the way I design the workflow.

Thanks to your explanation, I think I might have a better view of the message flows now.

I’m using Python, Django and Camunda REST API to interact with Camunda Engine. Maybe I will try put everything in the same pool and use different lanes.

I’ll also have a look to see if there is any way I can use Python script to trigger it.

Thank you very much for the help

5

If you’re not using Java, an you should consider using the OpenAPI documentation to generate your python calls.
It 'll save you a lot of time coding REST Calls.

6

Hi @aravindhrs

Thank you for your quick response. The example you provided is quite helpful.

I should think about learning a bit of Java so I can understand how Camunda works better. I’ll try to check if there is anyway I can use Python script to do the same thing.

Thank you for the help.

7

Thank you @Niall I will check OpenAPI documentation and see if it could help in my workflow.

Cheers.

8