Input & Transitions

Input data and transitions, in particular conditional transitions, are an important part in Direktiv. As previously shown a state can define a transition as the next state in the flow. If there is no transition defined the flow ends at that point in the execution. So far the examples have only shown sequential transition but here there will be a conditional transition based on input data of the flow.

Conditional Transition

To execute conditional transitions Direktiv provides a switch which makes decisions about where to transition to next based on the instance data by evaluating a number of jq or js expressions and checking the results.

direktiv_api: workflow/v1

states:
- id: ifelse
  type: switch
  conditions:
  - condition: 'jq(.age > 17)'
    transition: accepted
  - condition: 'jq(.age != null)'
    transition: rejected
  defaultTransition: failure

- id: accepted
  type: noop
  transform:
    message: request accepted

- id: rejected
  type: noop
  transform:
    message: rejected based on age

- id: failure
  type: error
  error: age.error
  message: no age provided

Each of the conditions will be evaluated in the order it appears by running the jq command in condition. Any result other than null, false, {}, [], "", or 0 will cause the condition to be considered a successful match. If no conditions match the default transition will be used.

Transform

Each condition has a transform attribute and there is a defaultTransform so every condition can modfiy the state data if there is a successful match.

Running the above example will always go to the failure state because no input data has been provided for this flow. In this case the failure state is an error state which marks the flow as failed. More about errors can be found in the error handling section.

Input Data

To make the above example more useful the flow needs input data. Input data in Direktiv will never be empty. If the flow is called with no data it will be executed with an empty JSON object {}. If the payload is in JSON format it will be base64 encoded and provided with the attribute input.

{
  "input": "T1hSisBaSE64Data=="
}

The above flow can be called with a simple JSON providing a value for age.

{ 
    "age": 18
}

The curl command to call the flow via the API is the following. Please adjust the flow and server name if required.

curl -X POST http://localhost:8080/api/namespaces/demo/tree/MYWORKFLOWNAME?op=wait \
--data-binary @- << EOF
{ 
    "age": 18
}
EOF

The response is always the last state data of a flow. Because the final states include a transform the response of the flow would be the transformed data.

{
  "message": "request accepted"
}