Do While
The Do While task (DO_WHILE) sequentially executes a list of tasks as long as a given condition is true. The sequence of tasks gets executed before the condition is checked, even for the first iteration, just like a regular do.. while statement in programming.
Task parameters
Use these parameters in top level of the Do While task configuration.
| Parameter | Type | Description | Required / Optional |
|---|---|---|---|
| loopCondition | String | The condition that is evaluated after each iteration. This is a JavaScript expression, evaluated using the Nashorn engine. | Required. |
| loopOver | List[Task] | The list of task configurations that will be executed as long as the condition is true. | Required. |
JSON configuration
Here is the task configuration for a Do While task.
{
"name": "do_while",
"taskReferenceName": "do_while_ref",
"inputParameters": {},
"type": "DO_WHILE",
"loopCondition": "(function () {\n if ($.do_while_ref['iteration'] < 5) {\n return true;\n }\n return false;\n})();",
"loopOver": [ // List of tasks to be executed in the loop
{
// task configuration
},
{
// task configuration
}
]
}
Output
The Do While task will return the following parameters.
| Name | Type | Description |
|---|---|---|
| iteration | Integer | The number of iterations. If the Do While task is in progress, iteration will show the current iteration number. When completed, iteration will show the final number of iterations. |
In addition, a map will be created for each iteration, keyed by its iteration number (e.g., 1, 2, 3), and will contain the task outputs for all of the loopOver tasks.
Furthermore, if loopCondition declares any parameter, it will also appear in the output. For example, storage will appear in the output if loopCondition is if ($.LoopTask['iteration'] <= 10) {$.LoopTask.storage = 3; true } else {false}.
Execution
When a Do While loop is executed, each task in the loop will have its taskReferenceName concatenated with __i, with i as the iteration number starting at 1. If one of the loop tasks fails, the Do While task status will be set as FAILED, and upon retry, the iteration number will restart from 1.
Each loop task output is stored as part of the Do While task, indexed by the iteration value, allowing loopCondition to reference the output of a task for a specific iteration (e.g., $.LoopTask['iteration]['first_task']).
Examples
Here are some examples for using the Do While task.
Using a basic script
In this example task configuration, the Do While task evaluates two criteria:
{
"name": "Loop",
"taskReferenceName": "LoopTask",
"type": "DO_WHILE",
"inputParameters": {
"value": "${workflow.input.value}"
},
"loopCondition": "if ( ($.LoopTask['iteration'] < $.value ) || ( $.first_task['response']['body'] > 10)) { false; } else { true; }",
"loopOver": [
{
"name": "firstTask",
"taskReferenceName": "first_task",
"inputParameters": {
"http_request": {
"uri": "http://localhost:8082",
"method": "POST"
}
},
"type": "HTTP"
},{
"name": "secondTask",
"taskReferenceName": "second_task",
"inputParameters": {
"http_request": {
"uri": "http://localhost:8082",
"method": "POST"
}
},
"type": "HTTP"
}
],
"startDelay": 0,
"optional": false
}
Assuming three executions occurred (first_task__1, first_task__2, first_task__3,
second_task__1, second_task__2, and second_task__3), the Do While task will return the following will produce the following output:
{
"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"
}
}
}
}
Using the iteration key in a loop task
Sometimes, you may want to use the Do While iteration value/counter inside your loop tasks. In this example, an API call is made to a GitHub repository to get all stargazers and each iteration increases the pagination.
To evaluate the current iteration, the parameter $.get_all_stars_loop_ref['iteration'] is used in loopCondition. In the HTTP task embedded in the loop, ${get_all_stars_loop_ref.output.iteration} is used to define which page the API should return.
{
"name": "get_all_stars",
"taskReferenceName": "get_all_stars_loop_ref",
"inputParameters": {
"stargazers": "4000"
},
"type": "DO_WHILE",
"loopCondition": "if ($.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"
}
]
}
Limitations
There are several limitations for the Do While task:
- Branching—Within a Do While task, branching using Switch, Fork/Join, Dynamic Fork tasks are supported. However, since the loop tasks will be executed within the scope of the Do While task, any branching that crosses outside its scope will not be respected.
- Nested loops—Nested Do While tasks are not supported. To achieve a similar functionality as a nested loop, you can use a Sub Workflow task inside the Do While task.
- Isolation group execution—Isolation group execution is not supported. However, domain is supported for loop tasks inside the Do While task.