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Child Workflows

Workflow::executeChildWorkflow and Workflow::newChildWorkflowStub enables the scheduling of other Workflows from within a Workflow's implementation. The parent Workflow has the ability to monitor and impact the lifecycle of the child Workflow, similar to the way it does for an Activity that it invoked.

// Use one stub per child workflow run
$child = Workflow::newChildWorkflowStub(
ChildWorkflowInterface::class,
ChildWorkflowOptions::new()
// Do not specify WorkflowId if you want Temporal to generate a unique Id
// for the child execution.
->withWorkflowId('BID-SIMPLE-CHILD-WORKFLOW')
->withExecutionStartToCloseTimeout(DateInterval::createFromDateString('30 minutes'))
);
// This is a non blocking call that returns immediately.
// Use yield $child->workflowMethod(name) to call synchronously.
$promise = $child->workflowMethod('value');
// Do something else here.
try{
$value = yield $promise;
} catch(TemporalException $e) {
$logger->error('child workflow failed');
throw $e;
}

Let's take a look at each component of this call.

Before calling $child->workflowMethod(), you must configure ChildWorkflowOptions for the invocation. These options customize various execution timeouts, and are passed into the workflow stub defined by the Workflow::newChildWorkflowStub. Once stub created you can invoke it's workflow method based on attribute WorkflowMethod.

The method call returns immediately and returns a Promise. This allows you to execute more code without having to wait for the scheduled Workflow to complete.

When you are ready to process the results of the Workflow, call the yield $promise method on the returned promise object.

When a parent Workflow is cancelled by the user, the child Workflow can be cancelled or abandoned based on a configurable child policy.

You can also skip the stub part of child workflow initiation and use Workflow::executeChildWorkflow directly:

// Use one stub per child workflow run
$childResult = yield Workflow::executeChildWorkflow(
'ChildWorkflowName',
['args'],
ChildWorkflowOptions::new()->withWorkflowId('BID-SIMPLE-CHILD-WORKFLOW'),
Type::TYPE_STRING // optional: defines the return type
);