Output of the function's updated data.

Matías Liñán García 25

Hi, I am working with the IoT Hub with an external device and I am using the Azure IoT Explorer application to view the telemetry from my device.

Using eventgrid I have related my function to receive the data from my IoT Hub. But how could I see the data coming out of the function?

Because nothing is coming to the instance of digital twins.

Best regards.

Matías Liñán García 25

I copy the code of the function in case you see any errors

// Default URL for triggering event grid function in the local environment.
// http://localhost:7071/runtime/webhooks/EventGrid?functionName={functionname}
using System;
using Azure;
using System.Net.Http;
using Microsoft.Azure.WebJobs;
using Azure.Core.Pipeline;
using Azure.DigitalTwins.Core;
using Azure.Identity;
using Microsoft.Azure.WebJobs.Extensions.EventGrid;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using Azure.Messaging.EventGrid;
using System.Threading.Tasks; 

namespace gemelo_app_uco2
{
    public class IoTHubtoTwins
    {
	private static readonly string adtInstanceUrl = Environment.GetEnvironmentVariable("ADT_SERVICE_URL");
        private static readonly HttpClient httpClient = new HttpClient();

        [FunctionName("IoTHubtoTwins")]

        public async Task Run([EventGridTrigger]EventGridEvent eventGridEvent, ILogger log)

	{
            if (adtInstanceUrl == null) log.LogError("Application setting \"ADT_SERVICE_URL\" not set");

            try
	    {
                // Authenticate with Digital Twins
                var cred = new DefaultAzureCredential();
                var client = new DigitalTwinsClient(new Uri(adtInstanceUrl?? throw new ArgumentNullException(nameof(adtInstanceUrl))), cred);
                log.LogInformation($"ADT service client connection created.");
            
                if (eventGridEvent != null && eventGridEvent.Data != null)

            {
        
            log.LogInformation(eventGridEvent.Data.ToString());

	    // <Find_device_ID_and_angle>
                    JObject deviceMessage = (JObject)JsonConvert.DeserializeObject(eventGridEvent.Data.ToString());
                    string deviceId = (string)deviceMessage["systemProperties"]["iothub-connection-device-id"];
                    var angle = deviceMessage["body"]["roll"]; //debería sustituir la variable Angle por roll. 
                    // </Find_device_ID_and_angle>

                    log.LogInformation($"Device:{deviceId} Angle is:{angle}");

                    // <Update_twin_with_device_angle>
                    var updateTwinData = new JsonPatchDocument();
                    updateTwinData.AppendReplace("/Angle", angle.Value<double>());
                    await client.UpdateDigitalTwinAsync(deviceId, updateTwinData);
                    // </Update_twin_with_device_angle>
                }
            }
            catch (Exception ex)
            {
                log.LogError($"Error in ingest function: {ex.Message}");
	    }
        }
    }
}

MayankBargali-MSFT 70,536 Reputation points

2023-06-29T07:31:42.8833333+00:00

@Matías Liñán García Thanks for reaching out. Can you please confirm if your function app is getting executed by reviewing the monitor logs in your function app? There could be multiple reasons as the function app is not getting triggered, triggered but failed, triggered and was successful. Once you have confirmed then it would help in further troubleshooting the issue from the specific service end.
Matías Liñán García 25 Reputation points

2023-06-29T07:51:59.1+00:00

Yes, my function application is working.
Matías Liñán García 25 Reputation points

2023-06-29T09:23:22.0166667+00:00

My problem really is that I have the external device sending data to the IoT Hub and I have linked the IoT Hub with the function through eventgrid and when I connect my external device, I see that the data arrives but in the instance of digital twins the value that should update the function is not reflected.

How can I solve this?
LeelaRajeshSayana-MSFT 16,046 Reputation points

2023-06-29T15:14:20.3566667+00:00

Hi @Matías Liñán García If the function fails to upload data due to any exception, the function app should have caught it in the catch block. Do you notice any errors logged on the Azure function?
MayankBargali-MSFT 70,536 Reputation points

2023-06-30T05:46:25.69+00:00

@Matías Liñán García As LeelaRajeshSayana-MSFT mention do you observe any exception in your run history or was the run status is Success. You can review the monitor logs as I mentioned in my previous comment.

If there is any failure, then please review your logs or for any unhandled exception please review the application insights logs to know more detail. You can also review the Diagnose and solve problem blade on your function app to is there are any failed run's to get more details and the action plan if any to resolve the issue.
Matías Liñán García 25 Reputation points

2023-06-30T06:20:33.49+00:00

Error in ingest function: Cannot access child value on Newtonsoft.Json.Linq.JValue.
rbrundritt 18,686 Reputation points Microsoft Employee

2023-06-30T15:02:36.3466667+00:00

If you haven't already, look into remote debugging your function: https://learn.microsoft.com/en-us/azure/azure-functions/functions-develop-vs?tabs=in-process#remote-debugging This has helped me solve a ton of issues with Azure services and functions that worked locally but had issues once deployed. You can add break points, walk through the code, and inspect data in real time to figure out what's wrong.

1 answer

LeelaRajeshSayana-MSFT 16,046 Reputation points

2023-06-30T15:45:05.61+00:00
Hi @Matías Liñán García Thank you for looking into this and sharing these updates. Here is a breakdown of what your function app code does. The error indicated that you are trying to access of property from the received event which does not exists. The following line of code could most likely have thrown that error.

var angle = deviceMessage["body"]["roll"];

This piece of code extracts the value set for the property "roll" from the event received to the event hub. For this to work as intended, the message event pushed from IoT Hub should have a property named roll in the message body. For example, here is a sample event I generated from my IoT Hub Device Simulator code referenced in Configure and run the simulation section {"Level_of_Material":67.7025913431787}. I have modified the telemetryDataPoint variable in the SendDeviceToCloudMessageAsync method of AzureIoTHub.cs class from the project as follows

var telemetryDataPoint = new { Level_of_Material = currentTemperature };

To capture this event, I should modify my function app line of code to var temperature = deviceMessage["body"]["Level_of_Material"];

Here is how the Digital Twin update works.

updateTwinData.AppendReplace("/Angle", angle.Value<double>());

This line of code is used to patch the property on the Azure Digital Twin. Make sure that the twin you are targeting has a property named Angel defined in its model. In my example above, I should have a property named Level_of_Material" on my Digital Twin. Please find the below image showing the twin properties I have defined.

await client.UpdateDigitalTwinAsync(deviceId, updateTwinData);

This event sends an update to the Digital Twin with the patch information. Notice that the deviceId we are using here is obtained from the message event delivered from IoT Hub. It could be possible that digital twin ID, which is $dtId, could be different from the device ID defined on IoT Hub. If it is different, make sure you provide the correct $dtId value here in the above code.

If everything is configured correctly, your Digital Twin update should work as expected.

Hope this helps! Please let us know if you have any additional questions or need further assistance on this.

If the response helped, please do click Accept Answer and Yes for the answer provided. Doing so would help other community members with similar issue identify the solution. I highly appreciate your contribution to the community.
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Matías Liñán García 25 Reputation points

2023-07-03T10:06:26.0566667+00:00

I attach a screenshot of Azure digital twins

to ask you some questions.

First, is the model I have declared correct?

Secondly, it doesn't let me access the data history which is the icon on the right side of the screen. Do you know why it happens?

Also with this command I tried to link the function to my digital twin instance but it didn't make any connection.

az dt endpoint create eventgrid --endpoint-name {endpoint_name} --eventgrid-resource-group {eventgrid_resource_group} --eventgrid-topic {eventgrid_topic_name} -n {instance_name}

And also what I don't understand is this part, how do I give an output to the function?

LeelaRajeshSayana-MSFT 16,046 Reputation points

2023-07-05T16:14:57.3166667+00:00

Hi @Matías Liñán García Greetings! Your model is correct.

Secondly, it doesn't let me access the data history which is the icon on the right side of the screen. Do you know why it happens?

To Utilize the data history explorer, I believe, you would need to connect your Azure Digital Twin instance to Azure data explorer. Please refer the article Azure Digital Twins data history with Azure Data Explorer for more details and guidance on this.

Please note that your Azure function does need any explicit output binding for the Digital Twin update to work. The update is done with in the code and not through the output binding. Please find the following integration of the function which I have used to update the Digital Twin successfully.

az dt endpoint create eventgrid --endpoint-name {endpoint_name} --eventgrid-resource-group {eventgrid_resource_group} --eventgrid-topic {eventgrid_topic_name} -n {instance_name}

Please note that the above command is used to establish a connection from Azure Digital Twin to an event grid topic. This is not associated with any Azure function.

Since you claim that you are receiving events from the Azure IoT Hub into the Azure function, I believe your Azure function is already connected with IoT Hub. This must be done using a command similar to the following.

az eventgrid event-subscription create --name <name-for-hub-event-subscription> --event-delivery-schema eventgridschema --source-resource-id /subscriptions/<your-subscription-ID>/resourceGroups/<your-resource-group>/providers/Microsoft.Devices/IotHubs/<your-IoT-hub> --included-event-types Microsoft.Devices.DeviceTelemetry --endpoint-type azurefunction --endpoint /subscriptions/<your-subscription-ID>/resourceGroups/<your-resource-group>/providers/Microsoft.Web/sites/<your-function-app>/functions/ProcessHubToDTEvents

One thing I would like to make a note is to check if the Azure function has correct access permissions to update the Azure Digital Twin. The function app needs to be assigned the Azure Digital Twins Data Owner role in the Azure Digital Twins instance. Please find the steps in the Assign Access Role to know the steps on how you can achieve this.

Hope this helps. Please let us know if you have any additional questions or need further clarification.

Matías Liñán García 25 Reputation points

2023-07-06T08:30:44.85+00:00

Hi, I still can't see the update of my property, I have checked both the function and all the roles I should have and I still get the same error.

Executed 'IoTHubtoTwins' (Succeeded, Id=41...-a235-46b6-b61a-6cec114386a6, Duration=1ms)

9:47:55 | Trace

@dbd679437e65989...e78c1eca85ef87b

Error in ingest function: Cannot access child value on Newtonsoft.Json.Linq.JValue.

9:47:55 | Trace

@dbd679437e65989...e78c1eca85ef87b

{"properties":{},"systemProperties":{"ioth...tZXRlclkiOjIsImFjY2VsZXJvbWV0ZXJaIjo3fQ=="}

9:47:55 | Trace

@dbd679437e65989...e78c1eca85ef87b

ADT service client connection created.

9:47:55 | Trace

@dbd679437e65989...e78c1eca85ef87b

Executing 'IoTHubtoTwins' (Reason='EventGr...', Id=4189e7ec-a235-46b6-b61a-6cec114386a6)

And I would also like to know if it is normal for the angle property to always let me change it from there.

I have been watching other tutorials and it is not normal for it to appear like that:

And finally I would like to know how I can see the log of the function?

Thank you very much for your help.

Matías Liñán García 25 Reputation points

2023-07-06T08:51:13.87+00:00

Also when I run this command:

PS C:\WINDOWS\gemelo-app-uco2> az dt twin query --query-command "SELECT * FROM digitaltwins WHERE \$dtId = 'Inclinometro'" --dt-name <DTinstance>.digitaltwins.azure.net { "result": [] }

I should see the information of the digital twin and nothing appears.

LeelaRajeshSayana-MSFT 16,046 Reputation points

2023-07-06T14:17:14.1833333+00:00

Hello @Matías Liñán García Thank you for your response. It looks like you are trying to execute the command through Windows PowerShell. I noticed a similar result when I executed the command in PowerShell. Try windows command prompt instead.

You wouldn't need escape character \ infront of dtId in command prompt.

Here is the command you can use, az dt twin query --query-command "SELECT * FROM digitaltwins WHERE $dtId = '<ID>'" --dt-name <DTinstance>.digitaltwins.azure.net

The error Cannot access child value on Newtonsoft.Json.Linq.JValue still implies that we are trying to access a property from the object that does not exist or it is in a different format. Before you extract the angle using the line var angle = deviceMessage["body"]["roll"]; add a logger statement to inspect what is the deviceMessage that has been received by the function. You can do this by adding the following line log.LogInformation($"Received message from device {deviceId}: {deviceMessage}");

I also recommend to look into Debug Azure functions locally as it provides additional insights on how your code is functioning and you can inspect the data at each step.

You can certainly change the property value on the portal for testing purposes. But the beats the use case you are trying to achieve, which is to push data from Azure IoT Hub.

I believe the second image you have added shows the fields defined as Telemetry instead of Property in the device model. Hence you see a difference in the UI. I hope this clarifies.

Please let us know if you need any additional assistance.

Matías Liñán García 25 Reputation points

2023-07-11T08:25:25.12+00:00

Hi, I keep getting the same error.

I will attach how I am receiving the telemetry both by IoT explorer and by the console.

In my function if I put:

var Angle = ["body"]["roll"]; which would be how it comes in IoT Explorer but I get the same error Error in ingest function: Cannot access child value on Newtonsoft.Json.Linq.JValue.

If I put it as in the console:

var Angle = ["event"]["payload"]["roll"]; not even the information message appears.

I know what my mistake is that it may not find the data because I am not addressing it right. Is there no way to see in IoTHub what is actually coming to it?

I have another question too, when the value is updated the idea would be that my twin would be tilted at the angle it is telling us when updating it, as my twin is a tilting platform.

And right now my 3d scenes model moves the platform all the time and I would like to know if there is a way to make it move only when the angle is updated.
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Output of the function's updated data.

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