add call child workflow sample (#644)

Signed-off-by: MregXN <[email protected]>

examples/workflow/README.md

@@ -143,3 +143,25 @@ Job 'job1' is unhealthy.
 ```
 
 This workflow runs forever or until you press `ENTER` to stop it. Starting the app again after stopping it will cause the same workflow instance to resume where it left off.
+
+### Child Workflow
+
+This example demonstrates how to call a child workflow. The Dapr CLI can be started using the following command:
+
+```sh
+dapr run --app-id wfexample --dapr-grpc-port 50001
+```
+
+In a separate terminal window, run the following command to start the Python workflow app:
+
+```sh
+python3 child_workflow.py
+```
+
+When you run the example, you will see output like this:
+```
+...
+*** Calling child workflow 29a7592a1e874b07aad2bb58de309a51-child
+*** Child workflow 6feadc5370184b4998e50875b20084f6 called
+...
+```

examples/workflow/child_workflow.py

@@ -0,0 +1,44 @@
+# -*- coding: utf-8 -*-
+# Copyright 2023 The Dapr Authors
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#     http://www.apache.org/licenses/LICENSE-2.0
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import dapr.ext.workflow as wf
+import time
+
+def main_workflow(ctx: wf.DaprWorkflowContext):
+    try:
+        instance_id = ctx.instance_id
+        child_instance_id = instance_id + '-child'
+        print(f'*** Calling child workflow {child_instance_id}')
+        yield ctx.call_child_workflow(workflow=child_workflow,input=None,instance_id=child_instance_id)
+    except Exception as e:
+        print(f'*** Exception: {e}')
+
+    return
+
+def child_workflow(ctx: wf.DaprWorkflowContext):
+    instance_id = ctx.instance_id
+    print(f'*** Child workflow {instance_id} called')
+
+if __name__ == '__main__':
+    workflowRuntime = wf.WorkflowRuntime("localhost", "50001")
+    workflowRuntime.register_workflow(main_workflow)
+    workflowRuntime.register_workflow(child_workflow)
+    workflowRuntime.start()
+
+    wf_client = wf.DaprWorkflowClient()
+    instance_id = wf_client.schedule_new_workflow(
+        workflow=main_workflow)
+
+    # Wait for the workflow to complete
+    time.sleep(5)
+
+    workflowRuntime.shutdown()