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An example of creating a model extension for bpmn-js
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README.md

This example is part of our 📓 custom elements guide. Checkout the final result here.

bpmn-js Example: Model Extension

An example of creating a model extension for bpmn-js. Model extensions allow you to read, modify and write BPMN 2.0 diagrams that contain extension attributes and elements.

About

This example allows you to read, modify and write BPMN 2.0 diagrams that contain qa:suitable extension attributes and qa:analysisDetails extension elements. You can set the suitability score of each element.

Screenshot

Here's an example of a diagram:

<?xml version="1.0" encoding="UTF-8"?>
<bpmn2:definitions xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                   xmlns:bpmn2="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:qa="http://some-company/schema/bpmn/qa"
                   targetNamespace="http://activiti.org/bpmn"
                   id="ErrorHandling">
  <bpmn2:process id="Process_1">
    <bpmn2:task id="Task_1" name="Examine Situation" qa:suitable="0.7">
      <bpmn2:outgoing>SequenceFlow_1</bpmn2:outgoing>
      <bpmn2:extensionElements>
        <qa:analysisDetails lastChecked="2015-01-20" nextCheck="2015-07-15">
          <qa:comment author="Klaus">
            Our operators always have a hard time to figure out, what they need to do here.
          </qa:comment>
          <qa:comment author="Walter">
            I believe this can be split up in a number of activities and partly automated.
          </qa:comment>
        </qa:analysisDetails>
      </bpmn2:extensionElements>
    </bpmn2:task>
    ...
  </bpmn2:process>
  <bpmndi:BPMNDiagram id="BPMNDiagram_1">
    ...
  </bpmndi:BPMNDiagram>
</bpmn2:definitions>

Check out the entire diagram here.

Creating a Model Extension

Our extension of BPMN 2.0 will be defined in a JSON file:

{
  "name": "QualityAssurance",
  "uri": "http://some-company/schema/bpmn/qa",
  "prefix": "qa",
  "xml": {
    "tagAlias": "lowerCase"
  },
  "types": [
    {
      "name": "AnalyzedNode",
      "extends": [
        "bpmn:FlowNode"
      ],
      "properties": [
        {
          "name": "suitable",
          "isAttr": true,
          "type": "Float"
        }
      ]
    },
    {
      "name": "AnalysisDetails",
      "superClass": [ "Element" ],
      "properties": [
        {
          "name": "lastChecked",
          "isAttr": true,
          "type": "String"
        },
        {
          "name": "nextCheck",
          "isAttr": true,
          "type": "String"
        },
        {
          "name": "comments",
          "isMany": true,
          "type": "Comment"
        }
      ]
    },
    ...
  ],
  ...
}

Check out the entire extension here.

A few things are worth noting here:

  • You can extend existing types using the "extends" property.
  • If you want to add extension elements to bpmn:ExtensionElements they have to have "superClass": [ "Element" ].

For more information about model extensions head over to moddle.

Next, let's add our model extension to bpmn-js.

Adding the Model Extension to bpmn-js

When creating a new instance of bpmn-js we need to add our model extension using the moddleExtenions property:

import BpmnModeler from 'bpmn-js/lib/Modeler';

import qaExtension from '../resources/qaPackage.json';

const bpmnModeler = new BpmnModeler({
  moddleExtensions: {
    qa: qaExtension
  }
});

Our model extension will be used by bpmn-moddle which is part of bpmn-js.

Modifying Extension Attributes and Elements

bpmn-js can now read, modify and write extension attributes and elements that we defined in our model extension.

After importing a diagram you could for instance read qa:AnalysisDetails extension elements of BPMN 2.0 elements:

function getExtensionElement(element, type) {
  if (!element.extensionElements) {
    return;
  }

  return element.extensionElements.values.filter((extensionElement) => {
    return extensionElement.$instanceOf(type);
  })[0];
}

const businessObject = getBusinessObject(element);

const analysisDetails = getExtensionElement(businessObject, 'qa:AnalysisDetails');

In our example we can set the suitability score of each element:

const suitabilityScoreEl = document.getElementById('suitability-score');

const suitabilityScore = Number(suitabilityScoreEl.value);

if (isNaN(suitabilityScore)) {
  return;
}

const extensionElements = businessObject.extensionElements || moddle.create('bpmn:ExtensionElements');

let analysisDetails = getExtensionElement(businessObject, 'qa:AnalysisDetails');

if (!analysisDetails) {
  analysisDetails = moddle.create('qa:AnalysisDetails');

  extensionElements.get('values').push(analysisDetails);
}

analysisDetails.lastChecked = new Date().toISOString();

const modeling = bpmnModeler.get('modeling');

modeling.updateProperties(element, {
  extensionElements,
  suitable: suitabilityScore
});

Check out the entire code here.

Run the Example

You need a NodeJS development stack with npm installed to build the project.

To install all project dependencies execute

npm install

To start the example execute

npm start

To build the example into the public folder execute

npm run all

License

MIT

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