Do-While

"type" : "DO_WHILE"

The DO_WHILE task sequentially executes a list of tasks as long as a given condition is true. The list of tasks is executed first, before the condition is checked (the first iteration will always execute).

When scheduled, each task of this loop will see its taskReferenceName concatenated with __i, with i being the iteration number, starting at 1. Warning: taskReferenceName containing arithmetic operators must not be used.

Each task output is stored as part of the DO_WHILE task, indexed by the iteration value (see example below), allowing the condition to reference the output of a task for a specific iteration (eg. $.LoopTask['iteration]['first_task'])

The DO_WHILE task is set to FAILED as soon as one of the loopOver fails. In such case retry, iteration starts from 1.

Limitations

• Domain or isolation group execution is unsupported;
• Nested DO_WHILE is unsupported, however, DO_WHILE task supports SUB_WORKFLOW as loopOver task, so we can achieve similar functionality.
• Since loopover tasks will be executed in loop inside scope of parent do while task, crossing branching outside of DO_WHILE task is not respected.

Branching inside loopOver task is supported.

Configuration

The following fields must be specified at the top level of the task configuration.

name	type	description
loopCondition	String	Condition to be evaluated after every iteration. This is a Javascript expression, evaluated using the Nashorn engine. If an exception occurs during evaluation, the DO_WHILE task is set to FAILED_WITH_TERMINAL_ERROR.
loopOver	List[Task]	List of tasks that needs to be executed as long as the condition is true.

Output

name	type	description
iteration	Integer	Iteration number: the current one while executing; the final one once the loop is finished
i	Map[String, Any]	Iteration number as a string, mapped to the task references names and their output.
*	Any	Any state can be stored here if the loopCondition does so. For example storage will exist if loopCondition is if ($.LoopTask['iteration'] <= 10) {$.LoopTask.storage = 3; true } else {false}

Examples

Basic Example

The following definition:

{
    "name": "Loop Task",
    "taskReferenceName": "LoopTask",
    "type": "DO_WHILE",
    "inputParameters": {
      "value": "${workflow.input.value}"
    },
    "loopCondition": "if ( ($.LoopTask['iteration'] < $.value ) || ( $.first_task['response']['body'] > 10)) { false; } else { true; }",
    "loopOver": [
        {
            "name": "first task",
            "taskReferenceName": "first_task",
            "inputParameters": {
                "http_request": {
                    "uri": "http://localhost:8082",
                    "method": "POST"
                }
            },
            "type": "HTTP"
        },{
            "name": "second task",
            "taskReferenceName": "second_task",
            "inputParameters": {
                "http_request": {
                    "uri": "http://localhost:8082",
                    "method": "POST"
                }
            },
            "type": "HTTP"
        }
    ],
    "startDelay": 0,
    "optional": false
}

will produce the following execution, assuming 3 executions occurred (alongside first_task__1, first_task__2, first_task__3, second_task__1, second_task__2 and second_task__3):

{
    "taskType": "DO_WHILE",
    "outputData": {
        "iteration": 3,
        "1": {
            "first_task": {
                "response": {},
                "headers": {
                    "Content-Type": "application/json"
                }
            },
            "second_task": {
                "response": {},
                "headers": {
                    "Content-Type": "application/json"
                }
            }
        },
        "2": {
            "first_task": {
                "response": {},
                "headers": {
                    "Content-Type": "application/json"
                }
            },
            "second_task": {
                "response": {},
                "headers": {
                    "Content-Type": "application/json"
                }
            }
        },
        "3": {
            "first_task": {
                "response": {},
                "headers": {
                    "Content-Type": "application/json"
                }
            },
            "second_task": {
                "response": {},
                "headers": {
                    "Content-Type": "application/json"
                }
            }
        }
    }
}

Example using iteration key

Sometimes, you may want to use the iteration value/counter in the tasks used in the loop. In this example, an API call is made to GitHub (to the Conductor repository), but each loop increases the pagination.

The Loop taskReferenceName is "get_all_stars_loop_ref".

In the loopCondition the term $.get_all_stars_loop_ref['iteration'] is used.

In tasks embedded in the loop, ${get_all_stars_loop_ref.output.iteration} is used. In this case, it is used to define which page of results the API should return.

{
      "name": "get_all_stars",
      "taskReferenceName": "get_all_stars_loop_ref",
      "inputParameters": {
        "stargazers": "4000"
      },
      "type": "DO_WHILE",
      "decisionCases": {},
      "defaultCase": [],
      "forkTasks": [],
      "startDelay": 0,
      "joinOn": [],
      "optional": false,
      "defaultExclusiveJoinTask": [],
      "asyncComplete": false,
      "loopCondition": "if ($.get_all_stars_loop_ref['iteration'] < Math.ceil($.stargazers/100)) { true; } else { false; }",
      "loopOver": [
        {
          "name": "100_stargazers",
          "taskReferenceName": "hundred_stargazers_ref",
          "inputParameters": {
            "counter": "${get_all_stars_loop_ref.output.iteration}",
            "http_request": {
              "uri": "https://api.github.com/repos/ntflix/conductor/stargazers?page=${get_all_stars_loop_ref.output.iteration}&per_page=100",
              "method": "GET",
              "headers": {
                "Authorization": "token ${workflow.input.gh_token}",
                "Accept": "application/vnd.github.v3.star+json"
              }
            }
          },
          "type": "HTTP",
          "decisionCases": {},
          "defaultCase": [],
          "forkTasks": [],
          "startDelay": 0,
          "joinOn": [],
          "optional": false,
          "defaultExclusiveJoinTask": [],
          "asyncComplete": false,
          "loopOver": [],
          "retryCount": 3
        }
      ]
    }