iot-hub-csharp-csharp-twin-getstarted.md

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Get started with Azure IoT Hub device twins (.NET/.NET) | Microsoft Docs	How to use Azure IoT Hub device twins to add tags and then use an IoT Hub query. You use the Azure IoT device SDK for .NET to implement the simulated device app and the Azure IoT service SDK for .NET to implement a service app that adds the tags and runs the IoT Hub query.	robinsh	philmea	iot-hub	iot-hub	csharp	conceptual	08/26/2019	robinsh	mqtt, devx-track-csharp

Get started with device twins (.NET)

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In this tutorial, you create these .NET console apps:

• AddTagsAndQuery. This back-end app adds tags and queries device twins.

• ReportConnectivity. This device app simulates a device that connects to your IoT hub with the device identity created earlier, and reports its connectivity condition.

Note

The article Azure IoT SDKs provides information about the Azure IoT SDKs that you can use to build both device and back-end apps.

Prerequisites

• Visual Studio.

• An active Azure account. If you don't have an account, you can create a free account in just a couple of minutes.

• Make sure that port 8883 is open in your firewall. The device sample in this article uses MQTT protocol, which communicates over port 8883. This port may be blocked in some corporate and educational network environments. For more information and ways to work around this issue, see Connecting to IoT Hub (MQTT).

Create an IoT hub

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Register a new device in the IoT hub

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Get the IoT hub connection string

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[!INCLUDE iot-hub-include-find-custom-connection-string]

Create the service app

In this section, you create a .NET console app, using C#, that adds location metadata to the device twin associated with myDeviceId. It then queries the device twins stored in the IoT hub selecting the devices located in the US, and then the ones that reported a cellular connection.

1. In Visual Studio, select Create a new project. In Create new project, select Console App (.NET Framework), and then select Next.

2. In Configure your new project, name the project AddTagsAndQuery.

   

3. In Solution Explorer, right-click the AddTagsAndQuery project, and then select Manage NuGet Packages.

4. Select Browse and search for and select Microsoft.Azure.Devices. Select Install.

   

   This step downloads, installs, and adds a reference to the Azure IoT service SDK NuGet package and its dependencies.

5. Add the following using statements at the top of the Program.cs file:

   using Microsoft.Azure.Devices;

6. Add the following fields to the Program class. Replace {iot hub connection string} with the IoT Hub connection string that you copied in Get the IoT hub connection string.

   static RegistryManager registryManager;
   static string connectionString = "{iot hub connection string}";

7. Add the following method to the Program class:

   public static async Task AddTagsAndQuery()
   {
       var twin = await registryManager.GetTwinAsync("myDeviceId");
       var patch =
           @"{
               tags: {
                   location: {
                       region: 'US',
                       plant: 'Redmond43'
                   }
               }
           }";
       await registryManager.UpdateTwinAsync(twin.DeviceId, patch, twin.ETag);
   
       var query = registryManager.CreateQuery(
         "SELECT * FROM devices WHERE tags.location.plant = 'Redmond43'", 100);
       var twinsInRedmond43 = await query.GetNextAsTwinAsync();
       Console.WriteLine("Devices in Redmond43: {0}", 
         string.Join(", ", twinsInRedmond43.Select(t => t.DeviceId)));
   
       query = registryManager.CreateQuery("SELECT * FROM devices WHERE tags.location.plant = 'Redmond43' AND properties.reported.connectivity.type = 'cellular'", 100);
       var twinsInRedmond43UsingCellular = await query.GetNextAsTwinAsync();
       Console.WriteLine("Devices in Redmond43 using cellular network: {0}", 
         string.Join(", ", twinsInRedmond43UsingCellular.Select(t => t.DeviceId)));
   }

   The RegistryManager class exposes all the methods required to interact with device twins from the service. The previous code first initializes the registryManager object, then retrieves the device twin for myDeviceId, and finally updates its tags with the desired location information.

   After updating, it executes two queries: the first selects only the device twins of devices located in the Redmond43 plant, and the second refines the query to select only the devices that are also connected through cellular network.

   The previous code, when it creates the query object, specifies a maximum number of returned documents. The query object contains a HasMoreResults boolean property that you can use to invoke the GetNextAsTwinAsync methods multiple times to retrieve all results. A method called GetNextAsJson is available for results that are not device twins, for example, results of aggregation queries.

8. Finally, add the following lines to the Main method:

   registryManager = RegistryManager.CreateFromConnectionString(connectionString);
   AddTagsAndQuery().Wait();
   Console.WriteLine("Press Enter to exit.");
   Console.ReadLine();

9. Run this application by right-clicking on the AddTagsAndQuery project and selecting Debug, followed by Start new instance. You should see one device in the results for the query asking for all devices located in Redmond43 and none for the query that restricts the results to devices that use a cellular network.

   

In the next section, you create a device app that reports the connectivity information and changes the result of the query in the previous section.

Create the device app

In this section, you create a .NET console app that connects to your hub as myDeviceId, and then updates its reported properties to contain the information that it is connected using a cellular network.

1. In Visual Studio, select File > New > Project. In Create new project, choose Console App (.NET Framework), and then select Next.

2. In Configure your new project, name the project ReportConnectivity. For Solution, choose Add to solution, and then select Create.

3. In Solution Explorer, right-click the ReportConnectivity project, and then select Manage NuGet Packages.

4. Select Browse and search for and choose Microsoft.Azure.Devices.Client. Select Install.

   This step downloads, installs, and adds a reference to the Azure IoT device SDK NuGet package and its dependencies.

5. Add the following using statements at the top of the Program.cs file:

   using Microsoft.Azure.Devices.Client;
   using Microsoft.Azure.Devices.Shared;
   using Newtonsoft.Json;

6. Add the following fields to the Program class. Replace {device connection string} with the device connection string that you noted in Register a new device in the IoT hub.

   static string DeviceConnectionString = "HostName=<yourIotHubName>.azure-devices.net;DeviceId=<yourIotDeviceName>;SharedAccessKey=<yourIotDeviceAccessKey>";
   static DeviceClient Client = null;

7. Add the following method to the Program class:

   public static async void InitClient()
   {
       try
       {
           Console.WriteLine("Connecting to hub");
           Client = DeviceClient.CreateFromConnectionString(DeviceConnectionString, 
             TransportType.Mqtt);
           Console.WriteLine("Retrieving twin");
           await Client.GetTwinAsync();
       }
       catch (Exception ex)
       {
           Console.WriteLine();
           Console.WriteLine("Error in sample: {0}", ex.Message);
       }
   }

   The Client object exposes all the methods you require to interact with device twins from the device. The code shown above initializes the Client object, and then retrieves the device twin for myDeviceId.

8. Add the following method to the Program class:

   public static async void ReportConnectivity()
   {
       try
       {
           Console.WriteLine("Sending connectivity data as reported property");
   
           TwinCollection reportedProperties, connectivity;
           reportedProperties = new TwinCollection();
           connectivity = new TwinCollection();
           connectivity["type"] = "cellular";
           reportedProperties["connectivity"] = connectivity;
           await Client.UpdateReportedPropertiesAsync(reportedProperties);
       }
       catch (Exception ex)
       {
           Console.WriteLine();
           Console.WriteLine("Error in sample: {0}", ex.Message);
       }
   }

   The code above updates the reported property of myDeviceId with the connectivity information.

9. Finally, add the following lines to the Main method:

   try
   {
       InitClient();
       ReportConnectivity();
   }
   catch (Exception ex)
   {
       Console.WriteLine();
       Console.WriteLine("Error in sample: {0}", ex.Message);
   }
   Console.WriteLine("Press Enter to exit.");
   Console.ReadLine();

10. In Solution Explorer, right-click on your solution, and select Set StartUp Projects.

11. In Common Properties > Startup Project, select Multiple startup projects. For ReportConnectivity, select Start as the Action. Select OK to save your changes.

12. Run this app by right-clicking the ReportConnectivity project and selecting Debug, then Start new instance. You should see the app getting the twin information, and then sending connectivity as a reported property.

    

    After the device reported its connectivity information, it should appear in both queries.

13. Right-click the AddTagsAndQuery project and select Debug > Start new instance to run the queries again. This time, myDeviceId should appear in both query results.

    

Next steps

In this tutorial, you configured a new IoT hub in the Azure portal, and then created a device identity in the IoT hub's identity registry. You added device metadata as tags from a back-end app, and wrote a simulated device app to report device connectivity information in the device twin. You also learned how to query this information using the SQL-like IoT Hub query language.

You can learn more from the following resources:

• To learn how to send telemetry from devices, see the Send telemetry from a device to an IoT hub tutorial.

• To learn how to configure devices using device twin's desired properties, see the Use desired properties to configure devices tutorial.

• To learn how to control devices interactively, such as turning on a fan from a user-controlled app, see the Use direct methods tutorial.