Repeat on True(dowhile)

The current iterator feature allows a user to repeat an activity on a fixed number of times by configuring the iterate property. However, there are are certain scenarios where a user would like to repeat an activity based on the output of the current activity or previous activties. To support this, a new feature Repeat on true has been included as part of release 0.9.4.

Flow configuration

Repeat on True(dowhile) are associated with an activity. The activity must have the type declared and set to doWhile.

To begin with, the Repeat on true feature has two attributes under setting 1. condition: A boolean expression that can be built using the current activity’s output and previous activity’s outputs. 2. delay: The time in milliseconds to wait before executing the next iteration, by default, the delay is 0 implying there will be no delay between each iteration.

Along with the current and previous activities’ output, the value for condition can use a special attribute $iteration[index] to track the index of the iteration. This is often useful if the user does not want the activity to repeat indefinitely.

{
  "id": "rest_3",
  "name": "REST Invoke",
  "description": "Invokes a REST Service",
  "settings": {
     "condition": "$activity[RESTInvoke].data.username == \"Bret\" && $iteration[index]<=3",
     "delay": 2000
  },
  "type": "doWhile",
  "activity": {
    "ref": "#rest",
    "settings": {
      "method": "GET",
      "uri": "https://jsonplaceholder.typicode.com/users/1"
    }
  }
}

Important note: The condition evalucate after activity execution and $iteration[index] start with 0, which also means first execution must been made to determin next or not base on condition. The activity will always been execute $iteration[index] + 1 times

Since the activity is of type "doWhile", the condition attribute is evaluated to determine if/not the activity must be repeated. For the above activity, since the first part of the condition is always true for that url, the second part i.e $iteration[index]<=3 will determine if the activity needs to be repeated or not.