dapr-workflow-bpmn-generator

This repository contains an EXPERIMENTAL Source Generator that generates Dapr Workflows from BPMN 2.0 files. I created it to find out if we could translate BPMN workflows into Dapr Workflows. It not complete and is not ready to use in production scenarios.

Supported BPMN constructs

Category	Element	Supported
Participants	Pool
Sub Processes	Subprocess	Y
	Call Activity	Y
	Event Subprocess
	Transaction
Tasks	Service Task	Y
	User Task	Y
	Script Task	Y
	Business Rule Task
	Manual Task	Y
	Receive Task	Y
	Undefined Task
	Send Task	Y
	Receive Task (instantiated)
Gateways	Exclusive Gateway	Y
	Inclusive Gateway	Y
	Parallel Gateway	Y
	Event-based Gateway
	Complex Gateway

Events

Type	Normal Start	Sub process	Sub process non-interupted	Intermediate catch	Intermediate boundary	Intermediate boundary non-interrupt	Intermediate throw	End
None	Y	-	-	-	-	-	Y	Y
Message				Y			Y
Timer				Y		Y	-	-
Conditional				Y			-	-
Link	-	-	-	Y	-	-	Y	-
Signal
Error	-		-	-	Y	-	-
Escalation	-			-
Termination	-	-	-	-	-	-	-
Compensation			-	-		-
Cancel	-	-	-	-		-	-
Multiple
Multiple Parallel								-

How it works

• The Source Generator generates a DaprWorkflow for each Process in a BPMN file.
• A Dapr Workflow Activity is generated for each ServiceTask in the Process.
• For each supported flow element in the Process a private method is generated in the Workflow class.
• Each generated method returns the next methods to call.

This might sound a little abstract, so lets workout a simple example, lets write the Workflow manually using the following BPMN workflow:

<?xml version="1.0" encoding="UTF-8"?>
<bpmn:definitions xmlns:bpmn="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:dc="http://www.omg.org/spec/DD/20100524/DC" xmlns:di="http://www.omg.org/spec/DD/20100524/DI" xmlns:modeler="http://camunda.org/schema/modeler/1.0" id="Definitions_0x1ez33" targetNamespace="http://bpmn.io/schema/bpmn" exporter="Camunda Modeler" exporterVersion="5.16.0" modeler:executionPlatform="Camunda Cloud" modeler:executionPlatformVersion="8.3.0">
  <bpmn:process id="SampleProcess" isExecutable="true">
    <bpmn:startEvent id="StartEvent">
      <bpmn:outgoing>Flow_0zngdjw</bpmn:outgoing>
    </bpmn:startEvent>
    <bpmn:sequenceFlow id="Flow_0zngdjw" sourceRef="StartEvent" targetRef="RegisterContract" />
    <bpmn:serviceTask id="RegisterContract" name="Register Contract">
      <bpmn:incoming>Flow_0zngdjw</bpmn:incoming>
      <bpmn:outgoing>Flow_1js42u4</bpmn:outgoing>
    </bpmn:serviceTask>
    <bpmn:sequenceFlow id="Flow_1js42u4" sourceRef="RegisterContract" targetRef="SendContract" />
    <bpmn:serviceTask id="SendContract" name="Send Contract">
      <bpmn:incoming>Flow_1js42u4</bpmn:incoming>
      <bpmn:outgoing>Flow_17qojnt</bpmn:outgoing>
    </bpmn:serviceTask>
    <bpmn:endEvent id="EndEvent">
      <bpmn:incoming>Flow_17qojnt</bpmn:incoming>
    </bpmn:endEvent>
    <bpmn:sequenceFlow id="Flow_17qojnt" sourceRef="SendContract" targetRef="EndEvent" />
  </bpmn:process>
  <bpmndi:BPMNDiagram id="BPMNDiagram_1">
    <!-- omitted for clarity -->
  </bpmndi:BPMNDiagram>
</bpmn:definitions>

Now lets start and create some skeleton classes for the Dapr Workflow:

namespace Examples.Workflows;

using Dapr.Workflow;

public class SampleProcessWorkflow : Workflow<?, ?>
{
    public override Task<?> RunAsync(WorkflowContext context, ? input)
    {
        throw new NotImplementedException();
    }
}

public partial class RegisterContractActivity : WorkflowActivity<?, ?>
{
    public override Task<?> RunAsync(WorkflowActivityContext context, ? input)
    {
        throw new NotImplementedException();
    }
}

public partial class SendContractActivity : WorkflowActivity<?, ?>
{
    public override Task<?> RunAsync(WorkflowActivityContext context, ? input)
    {
        throw new NotImplementedException();
    }
}

As you can see there are some question marks in this code. Each Workflow and WorkflowActivity needs to define types for input and output. We need a way to define these types in the BPMN file because these types are often part of a shared model.

BPMN provides constructs for data modeling but they are very verbose. BPMN is extensible so lets define something simple first. We need to define the input and output types and names.

<?xml version="1.0" encoding="UTF-8"?>
<bpmn:definitions xmlns:bpmn="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:dc="http://www.omg.org/spec/DD/20100524/DC" xmlns:di="http://www.omg.org/spec/DD/20100524/DI" xmlns:modeler="http://camunda.org/schema/modeler/1.0" id="Definitions_0x1ez33" targetNamespace="http://bpmn.io/schema/bpmn" exporter="Camunda Modeler" exporterVersion="5.16.0" modeler:executionPlatform="Camunda Cloud" modeler:executionPlatformVersion="8.3.0">
  <bpmn:process id="SampleProcess" isExecutable="true">
    <bpmn:extensionElements>
        <dapr:inputOutput>
            <dapr:inputParameter name="" type="" />
            <dapr:outputParameter name="" type="" />
        </dapr:inputOutput>
    </bpmn:extensionElements>
    <bpmn:startEvent id="StartEvent">
      <bpmn:outgoing>Flow_0zngdjw</bpmn:outgoing>
    </bpmn:startEvent>
    <bpmn:sequenceFlow id="Flow_0zngdjw" sourceRef="StartEvent" targetRef="RegisterContract" />
    <bpmn:serviceTask id="RegisterContract" name="Register Contract">
      <bpmn:incoming>Flow_0zngdjw</bpmn:incoming>
      <bpmn:outgoing>Flow_1js42u4</bpmn:outgoing>
    </bpmn:serviceTask>
    <bpmn:sequenceFlow id="Flow_1js42u4" sourceRef="RegisterContract" targetRef="SendContract" />
    <bpmn:serviceTask id="SendContract" name="Send Contract">
      <bpmn:incoming>Flow_1js42u4</bpmn:incoming>
      <bpmn:outgoing>Flow_17qojnt</bpmn:outgoing>
    </bpmn:serviceTask>
    <bpmn:endEvent id="EndEvent">
      <bpmn:incoming>Flow_17qojnt</bpmn:incoming>
    </bpmn:endEvent>
    <bpmn:sequenceFlow id="Flow_17qojnt" sourceRef="SendContract" targetRef="EndEvent" />
  </bpmn:process>
  <bpmndi:BPMNDiagram id="BPMNDiagram_1">
    <!-- omitted for clarity -->
  </bpmndi:BPMNDiagram>
</bpmn:definitions>