Child Workflows

What is a Child Workflow?

A Child Workflow is a Workflow execution spawned from within a Workflow.

Child Workflows orchestrate invocations of Activities just like Workflows do.

Child Workflows should not be used for code organization, however they can be used to partition a Workflow execution's event history into smaller chunks which helps avoid the roughly ~50MB Workflow event history limit, amongst other use cases.

You should visit the workflows page to learn more about Workflows, their constraints, and their executions in general.

For more information about Child Workflows in general visit Temporal Child Workflows

Implementing Child Workflows

In this Clojure SDK programming model, a Temporal Workflow is a function declared with defworkflow

And a Child workflow is declared in the exact same way

Example

(require '[temporal.workflow :refer [defworkflow]])

(defworkflow my-workflow
    [{:keys [foo]}]
    ...)

Starting Child Workflow Executions

In this Clojure SDK, Workflows start Child Workflows with temporal.workflow/invoke

The options (ChildWorkflowOptions) provided to temporal.workflow/invoke are similar to the ones required to create a regular workflow with temporal.client.core/create-workflow

One big difference however is Child Workflows can provide options to control what happens to themselves with their parents close/fail/complete.

When a Parent Workflow Execution stops, the Temporal Cluster determines what will happen to any running child workflow executions based on the :parent-close-policy option.

See Temporal Parent Close Policy for more information

Example

(require '[temporal.workflow :refer [defworkflow]])
(require '[temporal.activity :refer [defactivity] :as a])

(defactivity child-greeter-activity
  [ctx {:keys [name] :as args}]
  (str "Hi, " name))

(defworkflow child-workflow
  [{:keys [names] :as args}]
  (for [name names]
     @(a/invoke child-greeter-activity {:name name})))

(defworkflow parent-workflow
  [args]
  @(w/invoke child-workflow args {:retry-options {:maximum-attempts 1}
                                  :workflow-task-timeout 10
                                  :workflow-execution-timeout 3600
                                  :workflow-run-timeout 3600}))