Error while executing "Ingest IoT Hub telemetry into Azure Digital Twins" documentation

Resma Pachikaran 16

The error while executing azure function : Error in ingest function: Cannot access child value on Newtonsoft.Json.Linq.JValue. Could you please help me with it.

MughundhanRaveendran-MSFT 12,421 Reputation points

2022-01-06T10:39:24.33+00:00

@Resma Pachikaran ,
Could you please provide the complete stack of the error message?
Are you seeing this error message while executing the function locally or after publishing to Azure functions runtime?
Resma Pachikaran 16 Reputation points

2022-01-06T10:42:34.293+00:00

2022-01-06T10:37:54.135 [Error] Error in ingest function: Cannot access child value on Newtonsoft.Json.Linq.JValue.2022-01-06T10:37:54.157 [Information] Executed 'IoTHubtoTwins' (Succeeded, Id=9cff88b9-79e4-4e45-893c-97d60fd0c009, Duration=47ms)2022-01-06T10:37:56.130 [Information] Executing 'IoTHubtoTwins' (Reason='EventGrid trigger fired at 2022-01-06T10:37:56.1304871+00:00', Id=4f6e518b-9546-4c74-8511-60ce0ff65992)2022-01-06T10:37:56.131 [Information] ADT service client connection created.2022-01-06T10:37:56.131 [Information] {"properties": {"temperatureAlert": "false"},"systemProperties": {"iothub-connection-device-id": "firstdevice","iothub-connection-auth-method": "{\"scope\":\"device\",\"type\":\"sas\",\"issuer\":\"iothub\",\"acceptingIpFilterRule\":null}","iothub-connection-auth-generation-id": "637725995472017566","iothub-enqueuedtime": "2022-01-06T10:37:53.734Z","iothub-message-source": "Telemetry"},"body": "eyJtZXNzYWdlSWQiOjQ1MSwiZGV2aWNlSWQiOiJSYXNwYmVycnkgUGkgV2ViIENsaWVudCIsInRlbXBlcmF0dXJlIjoyNS4zNzIwNDU5MjIyNzg1NTYsImh1bWlkaXR5Ijo3MS42NzAzNTczNzMwNTQxOX0="}2022-01-06T10:37:54.135 [Error] Error in ingest function: Cannot access child value on Newtonsoft.Json.Linq.JValue.

This error occurs after publishing to runtime
MughundhanRaveendran-MSFT 12,421 Reputation points

2022-01-06T10:52:19.317+00:00

@Resma Pachikaran , Thanks for the information. You have provided the invocation result. Complete stack would look like below
Resma Pachikaran 16 Reputation points

2022-01-06T11:06:19.86+00:00

Hi Thank you for your response. But I am not getting any errors while Debugging the code.
While executing the function in IoTHub I get this error.
MughundhanRaveendran-MSFT 12,421 Reputation points

2022-01-07T05:30:06.517+00:00

@Resma Pachikaran , It appears that the issue is arising from the code and not from the function platform. I would suggest you to add more logging to see which line of code is failing and fixing the error accordingly. Here are some similar discussions on this error message: https://stackoverflow.com/questions/43161432/c-sharp-cannot-access-child-value-on-newtonsoft-json-linq-jvalue

https://helperbyte.com/questions/137748/how-to-solve-the-error-cannot-access-child-value-on-newtonsoftjsonlinqjvalue
https://github.com/octokit/octokit.graphql.net/issues/234
Resma Pachikaran 16 Reputation points

2022-01-07T11:01:30.983+00:00

Thank you. I would like to add that I exactly followed the documentation.
MughundhanRaveendran-MSFT 12,421 Reputation points

2022-01-10T07:22:05.907+00:00

@Resma Pachikaran , Are you using the same code that is provided in this documentation ?
https://learn.microsoft.com/en-us/azure/digital-twins/how-to-ingest-iot-hub-data?tabs=cli
Resma Pachikaran 16 Reputation points

2022-01-10T07:34:28.78+00:00

Yes..the same one

Jorge Ramirez 20

Super late reply here, but I was having the same issue. The thing is the, string in your body section of the json is encoded in a base64 string. You first need to decode it, and then you'll have access to all the data you have passed in. In your example code above, I see that you passed:

{
  "messageId": 451,
  "deviceID": "Raspberry Pi Web Client",
  "temperature": 25.372045922278556,
  "humidity": 71.67035737305419
}

So what I do is first deserialize the first incoming message, then access the body field which is the base64 string, and decode and deserialize it, and now you'd have access to your data fields:

try
{
    var cred = new DefaultAzureCredential();
    var client = new DigitalTwinsClient(new Uri(adtInstanceUrl), cred);

    log.LogInformation($"ADT service client connection created");

    if (eventGridEvent != null && eventGridEvent.Data != null)
    {
        log.LogInformation(eventGridEvent.Data.ToString());

        var deviceMessage = (JObject)JsonConvert.DeserializeObject(eventGridEvent.Data.ToString());

        var decodedBytes = Convert.FromBase64String(deviceMessage["body"].ToString());
        var jsonString = Encoding.UTF8.GetString(decodedBytes);

        log.LogInformation(jsonString);

        var dataMessage = (JObject)JsonConvert.DeserializeObject(jsonString);

        // get our device id, temp and humidity from the object
        string deviceId = (string)deviceMessage["systemProperties"]["iothub-connection-device-id"];
        var messageId= dataMessage["messageId"];
        var deviceID= dataMessage["deviceID"];
        var temperature= dataMessage["temperature"];
        var humidity= dataMessage["humidity"];

        var updateTwinData = new JsonPatchDocument();
        updateTwinData.AppendReplace("/messageId", messageId.Value<double>());
        updateTwinData.AppendReplace("/deviceID", deviceID.Value<double>());
        updateTwinData.AppendReplace("/temperature", temperature.Value<double>());
        updateTwinData.AppendReplace("/humidity", humidity.Value<double>());

        await client.UpdateDigitalTwinAsync(deviceId, updateTwinData);
    }
}

Hope this helps.

2 answers

Ahsan Raza 1 Reputation point

2022-07-12T00:15:36.617+00:00

I am also having the same problem. Can you please help where the actual issue is?
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Reda Issa 1 Reputation point

2022-08-14T05:49:08.12+00:00

Facing the same issue. any help please
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