Triggering an conditional event after a event-based gateway

Neeniih · August 16, 2024, 8:15pm

Hello!

I’m trying the concept of event based gateway followed by a conditional event.
When testing I noticed the condition is triggered just fine if the condition is met right at the instance start. Otherwise, the condition simply isn’t triggered at all. For example this very simple diagram:

<?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:camunda="http://camunda.org/schema/1.0/bpmn" xmlns:di="http://www.omg.org/spec/DD/20100524/DI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:modeler="http://camunda.org/schema/modeler/1.0" id="Definitions_1cle6yz" targetNamespace="http://bpmn.io/schema/bpmn" exporter="Camunda Modeler" exporterVersion="5.26.0" modeler:executionPlatform="Camunda Platform" modeler:executionPlatformVersion="7.21.0">
  <bpmn:process id="Process_0it9vhi" isExecutable="true" camunda:historyTimeToLive="0">
    <bpmn:startEvent id="Event_17btlho">
      <bpmn:outgoing>Flow_0fap1rv</bpmn:outgoing>
    </bpmn:startEvent>
    <bpmn:sequenceFlow id="Flow_0fap1rv" sourceRef="Event_17btlho" targetRef="Gateway_0m3lol5" />
    <bpmn:intermediateCatchEvent id="Event_0w4rz0m">
      <bpmn:incoming>Flow_0s2d7gm</bpmn:incoming>
      <bpmn:outgoing>Flow_0d8l375</bpmn:outgoing>
      <bpmn:conditionalEventDefinition id="ConditionalEventDefinition_1pd3g4b" camunda:variableName="" camunda:variableEvents="">
        <bpmn:condition xsi:type="bpmn:tFormalExpression">${b &gt; a}</bpmn:condition>
      </bpmn:conditionalEventDefinition>
    </bpmn:intermediateCatchEvent>
    <bpmn:sequenceFlow id="Flow_0s2d7gm" sourceRef="Gateway_0m3lol5" targetRef="Event_0w4rz0m" />
    <bpmn:eventBasedGateway id="Gateway_0m3lol5">
      <bpmn:incoming>Flow_0fap1rv</bpmn:incoming>
      <bpmn:outgoing>Flow_0s2d7gm</bpmn:outgoing>
      <bpmn:outgoing>Flow_1xzu564</bpmn:outgoing>
    </bpmn:eventBasedGateway>
    <bpmn:sequenceFlow id="Flow_0d8l375" sourceRef="Event_0w4rz0m" targetRef="Activity_0ngulzr" />
    <bpmn:endEvent id="Event_16gqjmf">
      <bpmn:incoming>Flow_1q0pqru</bpmn:incoming>
    </bpmn:endEvent>
    <bpmn:sequenceFlow id="Flow_1q0pqru" sourceRef="Activity_0ngulzr" targetRef="Event_16gqjmf" />
    <bpmn:userTask id="Activity_0ngulzr">
      <bpmn:incoming>Flow_0d8l375</bpmn:incoming>
      <bpmn:outgoing>Flow_1q0pqru</bpmn:outgoing>
    </bpmn:userTask>
    <bpmn:intermediateCatchEvent id="Event_0m0qnu2">
      <bpmn:incoming>Flow_1xzu564</bpmn:incoming>
      <bpmn:outgoing>Flow_1q45xbt</bpmn:outgoing>
      <bpmn:timerEventDefinition id="TimerEventDefinition_0rj5dla">
        <bpmn:timeDuration xsi:type="bpmn:tFormalExpression">PT5M</bpmn:timeDuration>
      </bpmn:timerEventDefinition>
    </bpmn:intermediateCatchEvent>
    <bpmn:sequenceFlow id="Flow_1xzu564" sourceRef="Gateway_0m3lol5" targetRef="Event_0m0qnu2" />
    <bpmn:sequenceFlow id="Flow_1q45xbt" sourceRef="Event_0m0qnu2" targetRef="Activity_1ahdsaz" />
    <bpmn:userTask id="Activity_1ahdsaz">
      <bpmn:incoming>Flow_1q45xbt</bpmn:incoming>
      <bpmn:outgoing>Flow_12d7714</bpmn:outgoing>
    </bpmn:userTask>
    <bpmn:endEvent id="Event_1onmu7y">
      <bpmn:incoming>Flow_12d7714</bpmn:incoming>
    </bpmn:endEvent>
    <bpmn:sequenceFlow id="Flow_12d7714" sourceRef="Activity_1ahdsaz" targetRef="Event_1onmu7y" />
  </bpmn:process>
  <bpmndi:BPMNDiagram id="BPMNDiagram_1">
    <bpmndi:BPMNPlane id="BPMNPlane_1" bpmnElement="Process_0it9vhi">
      <bpmndi:BPMNShape id="Event_1uyrihp_di" bpmnElement="Event_0w4rz0m">
        <dc:Bounds x="382" y="92" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Event_17btlho_di" bpmnElement="Event_17btlho">
        <dc:Bounds x="152" y="92" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Gateway_1t3kgt8_di" bpmnElement="Gateway_0m3lol5">
        <dc:Bounds x="265" y="85" width="50" height="50" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Event_16gqjmf_di" bpmnElement="Event_16gqjmf">
        <dc:Bounds x="662" y="92" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Activity_0ns77ui_di" bpmnElement="Activity_0ngulzr">
        <dc:Bounds x="490" y="70" width="100" height="80" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Event_0m0qnu2_di" bpmnElement="Event_0m0qnu2">
        <dc:Bounds x="382" y="202" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Activity_14rtj8c_di" bpmnElement="Activity_1ahdsaz">
        <dc:Bounds x="490" y="180" width="100" height="80" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Event_1onmu7y_di" bpmnElement="Event_1onmu7y">
        <dc:Bounds x="662" y="202" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNEdge id="Flow_0s2d7gm_di" bpmnElement="Flow_0s2d7gm">
        <di:waypoint x="315" y="110" />
        <di:waypoint x="382" y="110" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_0fap1rv_di" bpmnElement="Flow_0fap1rv">
        <di:waypoint x="188" y="110" />
        <di:waypoint x="265" y="110" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_0d8l375_di" bpmnElement="Flow_0d8l375">
        <di:waypoint x="418" y="110" />
        <di:waypoint x="490" y="110" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_1q0pqru_di" bpmnElement="Flow_1q0pqru">
        <di:waypoint x="590" y="110" />
        <di:waypoint x="662" y="110" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_1xzu564_di" bpmnElement="Flow_1xzu564">
        <di:waypoint x="290" y="135" />
        <di:waypoint x="290" y="220" />
        <di:waypoint x="382" y="220" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_1q45xbt_di" bpmnElement="Flow_1q45xbt">
        <di:waypoint x="418" y="220" />
        <di:waypoint x="490" y="220" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_12d7714_di" bpmnElement="Flow_12d7714">
        <di:waypoint x="590" y="220" />
        <di:waypoint x="662" y="220" />
      </bpmndi:BPMNEdge>
    </bpmndi:BPMNPlane>
  </bpmndi:BPMNDiagram>
</bpmn:definitions>

If I start an process instance already with the variables “a = 1” and “b = 2”, the conditional event is triggered correctly.

It I try anything else, it doesn’t trigger at all:

Starting with one or no variable, then creating them after with the condition met
Starting with both variables but the condition not being met, then updating the values so the condition is met

I tried messing with async after and specifing the variables name and event on the conditional event but with no success.
Example of the config:

Result:

How can I make this conditional event trigger after the condition initial evaluation?

herrier · August 18, 2024, 9:44am

Hi @Neeniih - this stumped me too for a while! I compared your model against one of the conditional test case models in the code base and noticed a difference:

Remove the attributes “camunda:variableName” and “camunda:VariableEvents” from your XML model definition and it will start behaving as you expect. This looks like a bug in the modeller to me (I haven’t checked if its a known issue yet). By adding these attributes with “” values this is telling the engine - “don’t subscribe to any variable change events at all” which is very confusing and not what you’d expect by looking only at the properties panel of the modeller.

This is not related to the event gateway at all - same issue if you just have a simple start → conditional → terminate model. Likewise, you can take out all the continuations too.

Hope that helps!

Neeniih · August 19, 2024, 3:00pm

Hey, @herrier , removed it and it worked! What a nasty bug.

However, I wonder if that is the expected behaviour since I tried setting the variables name and event to specific variables and it stopped working again:

<?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:camunda="http://camunda.org/schema/1.0/bpmn" xmlns:di="http://www.omg.org/spec/DD/20100524/DI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:modeler="http://camunda.org/schema/modeler/1.0" id="Definitions_1cle6yz" targetNamespace="http://bpmn.io/schema/bpmn" exporter="Camunda Modeler" exporterVersion="5.26.0" modeler:executionPlatform="Camunda Platform" modeler:executionPlatformVersion="7.21.0">
  <bpmn:process id="Process_0it9vhi" isExecutable="true" camunda:historyTimeToLive="0">
    <bpmn:startEvent id="Event_17btlho">
      <bpmn:outgoing>Flow_0fap1rv</bpmn:outgoing>
    </bpmn:startEvent>
    <bpmn:sequenceFlow id="Flow_0fap1rv" sourceRef="Event_17btlho" targetRef="Gateway_0m3lol5" />
    <bpmn:intermediateCatchEvent id="Event_0w4rz0m">
      <bpmn:incoming>Flow_0s2d7gm</bpmn:incoming>
      <bpmn:outgoing>Flow_0d8l375</bpmn:outgoing>
      <bpmn:conditionalEventDefinition id="ConditionalEventDefinition_1pd3g4b" camunda:variableName="a,b" camunda:variableEvents="create,update,delete">
        <bpmn:condition xsi:type="bpmn:tFormalExpression">${b &gt; a}</bpmn:condition>
      </bpmn:conditionalEventDefinition>
    </bpmn:intermediateCatchEvent>
    <bpmn:sequenceFlow id="Flow_0s2d7gm" sourceRef="Gateway_0m3lol5" targetRef="Event_0w4rz0m" />
    <bpmn:eventBasedGateway id="Gateway_0m3lol5">
      <bpmn:incoming>Flow_0fap1rv</bpmn:incoming>
      <bpmn:outgoing>Flow_0s2d7gm</bpmn:outgoing>
      <bpmn:outgoing>Flow_1xzu564</bpmn:outgoing>
    </bpmn:eventBasedGateway>
    <bpmn:sequenceFlow id="Flow_0d8l375" sourceRef="Event_0w4rz0m" targetRef="Activity_0ngulzr" />
    <bpmn:endEvent id="Event_16gqjmf">
      <bpmn:incoming>Flow_1q0pqru</bpmn:incoming>
    </bpmn:endEvent>
    <bpmn:sequenceFlow id="Flow_1q0pqru" sourceRef="Activity_0ngulzr" targetRef="Event_16gqjmf" />
    <bpmn:userTask id="Activity_0ngulzr">
      <bpmn:incoming>Flow_0d8l375</bpmn:incoming>
      <bpmn:outgoing>Flow_1q0pqru</bpmn:outgoing>
    </bpmn:userTask>
    <bpmn:intermediateCatchEvent id="Event_0m0qnu2">
      <bpmn:incoming>Flow_1xzu564</bpmn:incoming>
      <bpmn:outgoing>Flow_1q45xbt</bpmn:outgoing>
      <bpmn:timerEventDefinition id="TimerEventDefinition_0rj5dla">
        <bpmn:timeDuration xsi:type="bpmn:tFormalExpression">PT5M</bpmn:timeDuration>
      </bpmn:timerEventDefinition>
    </bpmn:intermediateCatchEvent>
    <bpmn:sequenceFlow id="Flow_1xzu564" sourceRef="Gateway_0m3lol5" targetRef="Event_0m0qnu2" />
    <bpmn:sequenceFlow id="Flow_1q45xbt" sourceRef="Event_0m0qnu2" targetRef="Activity_1ahdsaz" />
    <bpmn:userTask id="Activity_1ahdsaz">
      <bpmn:incoming>Flow_1q45xbt</bpmn:incoming>
      <bpmn:outgoing>Flow_12d7714</bpmn:outgoing>
    </bpmn:userTask>
    <bpmn:endEvent id="Event_1onmu7y">
      <bpmn:incoming>Flow_12d7714</bpmn:incoming>
    </bpmn:endEvent>
    <bpmn:sequenceFlow id="Flow_12d7714" sourceRef="Activity_1ahdsaz" targetRef="Event_1onmu7y" />
  </bpmn:process>
  <bpmndi:BPMNDiagram id="BPMNDiagram_1">
    <bpmndi:BPMNPlane id="BPMNPlane_1" bpmnElement="Process_0it9vhi">
      <bpmndi:BPMNShape id="Event_17btlho_di" bpmnElement="Event_17btlho">
        <dc:Bounds x="152" y="92" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Event_1uyrihp_di" bpmnElement="Event_0w4rz0m">
        <dc:Bounds x="382" y="92" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Gateway_1t3kgt8_di" bpmnElement="Gateway_0m3lol5">
        <dc:Bounds x="265" y="85" width="50" height="50" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Event_16gqjmf_di" bpmnElement="Event_16gqjmf">
        <dc:Bounds x="662" y="92" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Activity_0ns77ui_di" bpmnElement="Activity_0ngulzr">
        <dc:Bounds x="490" y="70" width="100" height="80" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Event_0m0qnu2_di" bpmnElement="Event_0m0qnu2">
        <dc:Bounds x="382" y="202" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Activity_14rtj8c_di" bpmnElement="Activity_1ahdsaz">
        <dc:Bounds x="490" y="180" width="100" height="80" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Event_1onmu7y_di" bpmnElement="Event_1onmu7y">
        <dc:Bounds x="662" y="202" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNEdge id="Flow_0fap1rv_di" bpmnElement="Flow_0fap1rv">
        <di:waypoint x="188" y="110" />
        <di:waypoint x="265" y="110" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_0s2d7gm_di" bpmnElement="Flow_0s2d7gm">
        <di:waypoint x="315" y="110" />
        <di:waypoint x="382" y="110" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_0d8l375_di" bpmnElement="Flow_0d8l375">
        <di:waypoint x="418" y="110" />
        <di:waypoint x="490" y="110" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_1q0pqru_di" bpmnElement="Flow_1q0pqru">
        <di:waypoint x="590" y="110" />
        <di:waypoint x="662" y="110" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_1xzu564_di" bpmnElement="Flow_1xzu564">
        <di:waypoint x="290" y="135" />
        <di:waypoint x="290" y="220" />
        <di:waypoint x="382" y="220" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_1q45xbt_di" bpmnElement="Flow_1q45xbt">
        <di:waypoint x="418" y="220" />
        <di:waypoint x="490" y="220" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_12d7714_di" bpmnElement="Flow_12d7714">
        <di:waypoint x="590" y="220" />
        <di:waypoint x="662" y="220" />
      </bpmndi:BPMNEdge>
    </bpmndi:BPMNPlane>
  </bpmndi:BPMNDiagram>
</bpmn:definitions>

How it’s configurated:

Result:

Made some more testing and it seems to work fine with only one variable but not with two or more.
Config:

Result:

It’s a shame not being able to fully explore this feature since the productive ambient is heavily performance-oriented and I believe this would help a lot in that aspect.

Any Camunda Staff can confirm if it’s a known issue or should I open a request?

herrier · August 19, 2024, 3:33pm

Hey, yes, you can only specify a single variable in camunda:variableName. If you have an expression in your conditional that references multiple variables then you will have to leave this empty so that the condition is re-evaluated on any variable change. It doesn’t support comma separated list of variables (would be nice if it did though I think).

system · August 26, 2024, 3:34pm

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