# External Events

This tutorial demonstrates how to author a workflow where the workflow will wait until it receives an external event. This pattern is often applied in workflows that require an approval step. For more information about the external system interaction pattern see the [Dapr docs](https://docs.dapr.io/developing-applications/building-blocks/workflow/workflow-patterns/#external-system-interaction).

## Inspect the code

Open the `ExternalEventsWorkflow.cs` file in the `tutorials/workflow/csharp/external-system-interaction/ExternalEvents` folder. This file contains the definition for the workflow.

```mermaid
graph LR
   SW((Start
   Workflow))
   IF1{Is TotalPrice
    > 250?}
   IF2{Is Order Approved
   or TotalPrice < 250?}
   WAIT[Wait for
   approval event]
   EX{Event
   received?}
   PO[Process Order]
   SN[Send Notification]
   EW((End
   Workflow))
   SW --> IF1
   IF1 -->|Yes| WAIT
   IF1 -->|No| IF2
   EX -->|Yes| IF2
   EX -->|No| SN
   WAIT --> EX
   IF2 -->|Yes| PO
   PO --> SN
   IF2 -->|No| SN
   SN --> EW
```

## Run the tutorial

1. Use a terminal to navigate to the `tutorials/workflow/csharp/external-system-interaction` folder.
2. Build the project using the .NET CLI.

    ```bash
    dotnet build ./ExternalEvents/
    ```

3. Use the Dapr CLI to run the Dapr Multi-App run file

    ```bash
    dapr run -f .
    ```

4. Use the POST request in the [`externalevents.http`](./externalevents.http) file to start the workflow.
5. Use the GET request in the [`externalevents.http`](./externalevents.http) file to get the status of the workflow.
6. Stop the Dapr Multi-App run process by pressing `Ctrl+C`.