Fetch twin from Azure device sdk

Question

I need to just get the twin of a device using the Azure device sdk for node.js. I did used the Client clode as below:-

import { Client } from 'azure-iot-device';
import { Mqtt } from 'azure-iot-device-mqtt';
await client.setOptions(options);
await client.open();
const twin = await client.getTwin();

The issue is the twin returned doesn't have the device twin fields but other fields like below:-

{
  _events: [Object: null prototype] { newListener: [Function: bound ] },
  _eventsCount: 1,
  _maxListeners: undefined,
  _transport: Mqtt {
    _events: [Object: null prototype] {
      error: [Function],
      connected: [Function],
      disconnect: [Array],
      message: [Function],
      twinDesiredPropertiesUpdate: [Function: bound ]
    },
    _eventsCount: 5,
    _maxListeners: undefined,
    _mid: '',
    _firstConnection: false,
    _authenticationProvider: X509AuthenticationProvider { type: 0, _credentials: [Object] },
    _mqtt: MqttBase {
      _events: [Object: null prototype],
      _eventsCount: 2,
      _maxListeners: undefined,
      mqttProvider: [Object],
      _onTheWirePublishes: [OnTheWireMessageContainer],
      _fsm: [constructor],
      _options: [Object],
      _config: [Object],
      _mqttClient: [MqttClient],
      [Symbol(kCapture)]: false
    },
    _twinClient: MqttTwinClient {
      _events: [Object: null prototype],
      _eventsCount: 1,
      _maxListeners: undefined,
      _pendingTwinRequests: {},
      _mqtt: [MqttBase],
      _topicFsm: [BehavioralFsm],
      _responseTopic: [Object],
      _desiredPropertiesUpdatesTopic: [Object],
      [Symbol(kCapture)]: false
    },
    _fsm: constructor {
      initialState: 'disconnected',
      states: [Object],
      eventListeners: [Object],
      namespace: 'fsm.2',
      useSafeEmit: false,
      hierarchy: {},
      pendingDelegations: {},
      _stamped: true,
      inputQueue: [],
      targetReplayState: 'connected',
      state: 'connected',
      priorState: 'connecting',
      priorAction: 'connected.getTwin',
      currentAction: '',
      currentActionArgs: undefined,
      inExitHandler: false
    },
    _topicTelemetryPublish: 'devices/amidha/messages/events/',
    _topics: { method: [Object], message: [Object] },
    _userAgentString: 'azure-iot-device/1.17.1 (node v12.18.0; Ubuntu 18.04; x64)',
    [Symbol(kCapture)]: false
  },
  _retryPolicy: ExponentialBackOffWithJitter {
    _errorFilter: DefaultErrorFilter {
      ArgumentError: false,
      ArgumentOutOfRangeError: false,
      DeviceMaximumQueueDepthExceededError: false,
      DeviceNotFoundError: false,
      FormatError: false,
      UnauthorizedError: false,
      NotImplementedError: false,
      NotConnectedError: true,
      IotHubQuotaExceededError: false,
      MessageTooLargeError: false,
      InternalServerError: true,
      ServiceUnavailableError: true,
      IotHubNotFoundError: false,
      IoTHubSuspendedError: false,
      JobNotFoundError: false,
      TooManyDevicesError: false,
      ThrottlingError: true,
      DeviceAlreadyExistsError: false,
      DeviceMessageLockLostError: false,
      InvalidEtagError: false,
      InvalidOperationError: false,
      PreconditionFailedError: false,
      TimeoutError: true,
      BadDeviceResponseError: false,
      GatewayTimeoutError: false,
      DeviceTimeoutError: false,
      TwinRequestError: false
    },
    immediateFirstRetry: true,
    normalParameters: ExponentialBackoffWithJitterParameters {
      c: 100,
      cMin: 100,
      cMax: 10000,
      ju: 0.25,
      jd: 0.5
    },
    throttledParameters: ExponentialBackoffWithJitterParameters {
      c: 5000,
      cMin: 10000,
      cMax: 60000,
      ju: 0.25,
      jd: 0.5
    }
  },
  _maxOperationTimeout: 240000,
  desiredPropertiesUpdatesEnabled: false,
  properties: {
    reported: { update: [Function: update], '$version': 1 },
    desired: { '$version': 1 }
  },
  [Symbol(kCapture)]: false
}

I don't want to listen the twin change events that I can do easily by using above object using twin.on. I need to just get the current twin of the device. Is it possible?

Have you tried one of the [samples](https://github.com/Azure/azure-iot-sdk-node/blob/master/device/samples/simple_sample_device_twin.js)? — Matthijs van der Veer, Sep 11 '20 at 17:45
@iAviator, the code you posted does seem to differ from the sample I linked (the sample uses a callback method). But maybe you tried that one before. Is the output you put in your question a console.log(twin) ? Or something else? — Matthijs van der Veer, Sep 11 '20 at 18:58
So azure provides both the ways i.e. the callbacks and promise based. I used the promise based and I think both are same. And yes the output is twin console log. — iAviator, Sep 12 '20 at 00:19
When I use your code to reproduce this I see all the desired and reported properties (I added three properties to test it). It would seem Mark's answer is correct. — Matthijs van der Veer, Sep 14 '20 at 15:06
@MatthijsvanderVeer please revisit the question.I need to fetch the whole twin rather than just the desired or reported properties. My goal is to get the deviceScope property in twin which is not in the properties json object. — iAviator, Sep 14 '20 at 17:11

score 1 · Answer 1 · answered Sep 15 '20 at 05:31

After reading your comments it seems you are expecting some values to be there that just aren't available to the device (when you use the device SDK). The device can read and receive updates on desired properties and read/write to reported properties, the rest is unavailable.

In a comment, you mentioned you want to find the deviceScope in the twin, but that isn't available to the device SDK. You would need the service SDK for that.

When you print the result of const twin = await client.getTwin();, what you see is an object with helper methods to subscribe to desired property changes and patching new reported properties. Like Mark stated in his question, the properties of your twin are included in this object as well.

the response i printed has the properties in it and I already knew about it. I was just looking at ways to retrieve other properties of twin if there is any that is not documented by Azure but available and someone in the stackoverflow community has used it. I have confirmed this from Azure contributors too now.Check my answer for the link. — iAviator, Sep 15 '20 at 06:22

score 0 · Answer 2 · answered Sep 11 '20 at 17:32

0

The current twin is in the JSON you posted. See the section properties:

 properties: {
    reported: { update: [Function: update], '$version': 1 },
    desired: { '$version': 1 }
  },

The twin you posted is empty.

answered Sep 11 '20 at 17:32

Mark Radbourne

528
3
12

Please check again...it doesn't have all the fields – iAviator Sep 11 '20 at 17:41
And my question is to get the full twin which also contains other fields than desired and reported properties. – iAviator Sep 11 '20 at 17:41

iAviator · Accepted Answer · 2020-09-15T06:57:14.680

0

Above is not feasible to get the whole twin not just the desired and reported properties from device IoT sdk and that has been confirmed by Azure too. Check here.

The link also has a solution to assign parent child relationship between the leaf and the edge device.

edited Sep 15 '20 at 06:57

answered Sep 15 '20 at 06:26

iAviator

1,310
13
31

Fetch twin from Azure device sdk

3 Answers3