The next step was to enumerate all the EndDevices of a The Things Network(TTN) Application and display their attributes. I have to establish an Azure DeviceClient connection to an Azure IoT Hub for each TTN EndDevice to get downlink messages. To do this I will have to enumerate the TTN Applications in the instance then enumerate the LoRaWAN EndDevices.

using (HttpClient httpClient = new HttpClient())
{
	EndDeviceRegistryClient endDeviceRegistryClient = new EndDeviceRegistryClient(baseUrl, httpClient)
	{
		ApiKey = apiKey
	};

	try
	{
#if FIELDS_MINIMUM
		string[] fieldMaskPathsDevice = { "attributes" }; // think this is the bare minimum required for integration
#else
		string[] fieldMaskPathsDevice = { "name", "description", "attributes" };
#endif
		V3EndDevices endDevices = await endDeviceRegistryClient.ListAsync(applicationID, field_mask_paths:fieldMaskPathsDevice);
		if ((endDevices != null) && (endDevices.End_devices != null)) // If there are no devices returns null rather than empty list
		{
			foreach (V3EndDevice endDevice in endDevices.End_devices)
			{
#if FIELDS_MINIMUM
				Console.WriteLine($"EndDevice ID:{endDevice.Ids.Device_id}");
#else
				Console.WriteLine($"Device ID:{endDevice.Ids.Device_id} Name:{endDevice.Name} Description:{endDevice.Description}");
				Console.WriteLine($"  CreatedAt: {endDevice.Created_at:dd-MM-yy HH:mm:ss} UpdatedAt: {endDevice.Updated_at:dd-MM-yy HH:mm:ss}");
#endif
				if (endDevice.Attributes != null)
				{
					Console.WriteLine("  EndDevice attributes");

					foreach (KeyValuePair<string, string> attribute in endDevice.Attributes)
					{
						Console.WriteLine($"    Key: {attribute.Key} Value: {attribute.Value}");
					}
				}
				Console.WriteLine();
			}
		}
	}
	catch (Exception ex)
	{
		Console.WriteLine(ex.Message);
	}

	Console.WriteLine("Press <enter> to exit");
	Console.ReadLine();
}

Like the applicationRegistryClient.ListAsync call the endDeviceRegistryClient.ListAsync also returns null rather than an empty list.

I also wanted to explore whether I could use EndDevice attributes to populate the ClientOptions ModelId of my CreateFromConnectionString call. The modelId would contain the Digital Twins Definition Language(DTDL) ID of the LoRaWAN device so it could be automatically provisioned.