Conditional and Default Sequence Flows

Этот раздел перенесён из документации Camunda 7 и в дальнейшем будет доработан с учётом особенностей OpenBPM Engine

A sequence flow is the connector between two elements of a process. After an element is visited during process execution, all outgoing sequence flows are followed. This means that the default nature of BPMN 2.0 is to be parallel: <strong>two outgoing sequence flows will create two separate, parallel paths of execution.</strong>

<div data-bpmn-diagram="../bpmn/sequence-flow-parallel"></div>

Camunda Extensions

Attributes – Extension Elements <td> <a href="openbpm:engine:reference/bpmn20/custom-extensions/extension-elements.adoc#executionlistener">camunda:executionListener</a> </td>

Conditional Sequence Flow

A sequence flow can have a condition defined on it. When a BPMN 2.0 activity is left, the default behavior is to evaluate the conditions on the outgoing sequence flows. When a condition evaluates to 'true', that outgoing sequence flow is selected. When multiple sequence flows are selected that way, multiple executions will be generated and the process is continued in a parallel way. Note: This is different for gateways. Gateways will handle sequence flows with conditions in specific ways, depending on the gateway type.

<div data-bpmn-diagram="../bpmn/sequence-flow-conditional"></div>

A conditional sequence flow is represented in XML as a regular sequence flow, containing a conditionExpression sub-element. Note that at the moment only tFormalExpressions are supported. Omitting the xsi:type="" definition will simply default to this type of expression.

<sequenceFlow id="flow" sourceRef="theStart" targetRef="theTask">
  <conditionExpression xsi:type="tFormalExpression">
    <![CDATA[${order.price > 100 && order.price < 250}]]>
  </conditionExpression>
</sequenceFlow>

Currently, conditionalExpressions can be used with UEL and scripts. The expression or script used should resolve to a boolean value, otherwise an exception is thrown while evaluating the condition.

The example below references data of a process variable, in the typical JavaBean style through getters.

<conditionExpression xsi:type="tFormalExpression">
  <![CDATA[${order.price > 100 && order.price < 250}]]>
</conditionExpression>

This example invokes a method that resolves to a boolean value.

<conditionExpression xsi:type="tFormalExpression">
  <![CDATA[${order.isStandardOrder()}]]>
</conditionExpression>

In this example a simple groovy script is used to evaluate a process variable status.

<conditionExpression xsi:type="tFormalExpression" language="groovy">
  <![CDATA[status == 'complete']]>
</conditionExpression>

Similar to a script task, an external script resource can also be specified (see the documentation on script source for more information).

<conditionExpression xsi:type="tFormalExpression" language="groovy"
  camunda:resource="org/camunda/bpm/exampe/condition.groovy" />

Extensions for conditionExpression

Attributes <td> <a href="openbpm:engine:reference/bpmn20/custom-extensions/extension-attributes.adoc#resource">camunda:resource</a> </td> Extension Elements –

Default Sequence Flow

All BPMN 2.0 tasks and gateways can have a default sequence flow. This sequence flow is <strong>only</strong> selected as the outgoing sequence flow for that activity <strong>if</strong> none of the other sequence flows could be selected. Conditions on a default sequence flow are always ignored.

A default sequence flow for a certain activity is defined by the default attribute on that activity. The following example shows an exclusive gateway with a default sequence flow. Only when x is neither 1 nor 2 it will be selected as outgoing sequence flow for the gateway.

<div data-bpmn-diagram="../bpmn/exclusive-gateway"></div>

Note the 'slash' marker at the beginning of the default sequence flow. The corresponding XML snippet shows how flow4 is configured as a default sequence flow.

<exclusiveGateway id="exclusiveGw" name="Exclusive Gateway" default="flow4" />

<sequenceFlow id="flow2" sourceRef="exclusiveGw" targetRef="theTask1" name="${x==1}">
  <conditionExpression xsi:type="tFormalExpression">${x == 1}</conditionExpression>
</sequenceFlow>

<sequenceFlow id="flow3" sourceRef="exclusiveGw" targetRef="theTask2" name="${x==2}">
  <conditionExpression xsi:type="tFormalExpression">${x == 2}</conditionExpression>
</sequenceFlow>

<sequenceFlow id="flow4" sourceRef="exclusiveGw" targetRef="theTask3" name="else">
</sequenceFlow>

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Оригинал документации: https://docs.camunda.org