Switch

"type" : "SWITCH"

A SWITCH task is similar to the switch...case statement in a programming language. Two evaluators are supported. In either case, the expression is evaluated (this could be a simply a referefence to inputParameters, or a more complex Javascript expression), and the appropriate task is executed based on the output of the expression, and the decisionCases defined in the task configuration.

Use Cases

Useful in any situation where we have to execute one of many task options.

Configuration

The following parameters are specified at the top level of the task configuration.

name	type	description
evaluatorType	String (enum)	Type of the evaluator used. Supported types: value-param, javascript.
expression	String	Depends on the evaluatorType
decisionCases	Map[String, List[task]]	Map where the keys are the possible values that can result from expression being evaluated by evaluatorType with values being lists of tasks to be executed.
defaultCase	List[task]	List of tasks to be executed when no matching value if found in decisionCases

Note: If the evaluation type is value-param, inputParameters must be populated with the key specified in expression.

Evaluator Types and Expression

evaluatorType	expression	description
value-param	String (name of key)	Reference to provided key in inputParameters
javascript	String (JavaScript expression)	Evaluate JavaScript expressions and compute value

Output

name	type	description
evaluationResult	List[String]	A List of string representing the list of cases that matched.

Examples

In this example workflow, we have to ship a package with the shipping service providers on the basis of input provided while running the workflow.

Let's create a Workflow with the following switch task definition that uses value-param evaluatorType:

{
  "name": "switch_task",
  "taskReferenceName": "switch_task",
  "inputParameters": {
    "switchCaseValue": "${workflow.input.service}"
  },
  "type": "SWITCH",
  "evaluatorType": "value-param",
  "expression": "switchCaseValue",
  "defaultCase": [
    {
      ...
    }
  ],
  "decisionCases": {
    "fedex": [
      {
        ...
      }
    ],
    "ups": [
      {
        ...
      }
    ]
  }
}

In the definition above the value of the parameter switch_case_value is used to determine the switch-case. The evaluator type is value-param and the expression is a direct reference to the name of an input parameter. If the value of switch_case_value is fedex then the decision case ship_via_fedexis executed as shown below.

In a similar way - if the input was ups, then ship_via_ups will be executed. If none of the cases match then the default option is executed.

Here is an example using the javascript evaluator type:

{
  "name": "switch_task",
  "taskReferenceName": "switch_task",
  "inputParameters": {
    "inputValue": "${workflow.input.service}"
  },
  "type": "SWITCH",
  "evaluatorType": "javascript",
  "expression": "$.inputValue == 'fedex' ? 'fedex' : 'ups'",
  "defaultCase": [
    {
      ...
    }
  ],
  "decisionCases": {
    "fedex": [
      {
        ...
      }
    ],
    "ups": [
      {
        ...
      }
    ]
  }
}