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Get started with Azure IoT Hub device twins (Node) | 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 SDKs for Node.js to implement the simulated device app and a service app that adds the tags and runs the IoT Hub query.
fsautomata
iot-hub
iot-hub
nodejs
conceptual
08/25/2017
elioda

Get started with device twins (Node)

[!INCLUDE iot-hub-selector-twin-get-started]

At the end of this tutorial, you will have two Node.js console apps:

  • AddTagsAndQuery.js, a Node.js back-end app, which adds tags and queries device twins.
  • TwinSimulatedDevice.js, a Node.js app, which 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.

To complete this tutorial you need the following:

  • Node.js version 4.0.x or later.
  • An active Azure account. (If you don't have an account, you can create a free account in just a couple of minutes.)

Create an IoT hub

[!INCLUDE iot-hub-include-create-hub]

Retrieve connection string for IoT hub

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

[!INCLUDE iot-hub-get-started-create-device-identity]

Create the service app

In this section, you create a Node.js console app 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 are reporting a cellular connection.

  1. Create a new empty folder called addtagsandqueryapp. In the addtagsandqueryapp folder, create a new package.json file using the following command at your command prompt. Accept all the defaults:

    npm init

  2. At your command prompt in the addtagsandqueryapp folder, run the following command to install the azure-iothub package:

    npm install azure-iothub --save

  3. Using a text editor, create a new AddTagsAndQuery.js file in the addtagsandqueryapp folder.

  4. Add the following code to the AddTagsAndQuery.js file, and substitute the {iot hub connection string} placeholder with the IoT Hub connection string you copied when you created your hub:

     'use strict';
 var iothub = require('azure-iothub');
 var connectionString = '{iot hub connection string}';
 var registry = iothub.Registry.fromConnectionString(connectionString);

 registry.getTwin('myDeviceId', function(err, twin){
     if (err) {
         console.error(err.constructor.name + ': ' + err.message);
     } else {
         var patch = {
             tags: {
                 location: {
                     region: 'US',
                     plant: 'Redmond43'
               }
             }
         };

         twin.update(patch, function(err) {
           if (err) {
             console.error('Could not update twin: ' + err.constructor.name + ': ' + err.message);
           } else {
             console.log(twin.deviceId + ' twin updated successfully');
             queryTwins();
           }
         });
     }
 });

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

    After updating the tags it calls the queryTwins function.

  5. Add the following code at the end of AddTagsAndQuery.js to implement the queryTwins function:

     var queryTwins = function() {
     var query = registry.createQuery("SELECT * FROM devices WHERE tags.location.plant = 'Redmond43'", 100);
     query.nextAsTwin(function(err, results) {
         if (err) {
             console.error('Failed to fetch the results: ' + err.message);
         } else {
             console.log("Devices in Redmond43: " + results.map(function(twin) {return twin.deviceId}).join(','));
         }
     });

     query = registry.createQuery("SELECT * FROM devices WHERE tags.location.plant = 'Redmond43' AND properties.reported.connectivity.type = 'cellular'", 100);
     query.nextAsTwin(function(err, results) {
         if (err) {
             console.error('Failed to fetch the results: ' + err.message);
         } else {
             console.log("Devices in Redmond43 using cellular network: " + results.map(function(twin) {return twin.deviceId}).join(','));
         }
     });
 };

    The previous code 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 nextAsTwin methods multiple times to retrieve all results. A method called next is available for results that are not device twins, for example, results of aggregation queries.

  6. Run the application with:

     node AddTagsAndQuery.js

    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 Node.js console app that connects to your hub as myDeviceId, and then updates its device twin's reported properties to contain the information that it is connected using a cellular network.

  1. Create a new empty folder called reportconnectivity. In the reportconnectivity folder, create a new package.json file using the following command at your command prompt. Accept all the defaults:

    npm init

  2. At your command prompt in the reportconnectivity folder, run the following command to install the azure-iot-device, and azure-iot-device-mqtt package:

    npm install azure-iot-device azure-iot-device-mqtt --save

  3. Using a text editor, create a new ReportConnectivity.js file in the reportconnectivity folder.

  4. Add the following code to the ReportConnectivity.js file, and substitute the {device connection string} placeholder with the device connection string you copied when you created the myDeviceId device identity:

     'use strict';
 var Client = require('azure-iot-device').Client;
 var Protocol = require('azure-iot-device-mqtt').Mqtt;

 var connectionString = '{device connection string}';
 var client = Client.fromConnectionString(connectionString, Protocol);

 client.open(function(err) {
 if (err) {
     console.error('could not open IotHub client');
 }  else {
     console.log('client opened');

     client.getTwin(function(err, twin) {
     if (err) {
         console.error('could not get twin');
     } else {
         var patch = {
             connectivity: {
                 type: 'cellular'
             }
         };

         twin.properties.reported.update(patch, function(err) {
             if (err) {
                 console.error('could not update twin');
             } else {
                 console.log('twin state reported');
                 process.exit();
             }
         });
     }
     });
 }
 });

    The Client object exposes all the methods you require to interact with device twins from the device. The previous code, after it initializes the Client object, retrieves the device twin for myDeviceId and updates its reported property with the connectivity information.

  5. Run the device app

     node ReportConnectivity.js

    You should see the message twin state reported.

  6. Now that the device reported its connectivity information, it should appear in both queries. Go back in the addtagsandqueryapp folder and run the queries again:

     node AddTagsAndQuery.js

    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.

Use the following resources to learn how to: