Hello, I am editing the device twin of my test device using the Azure IoT hub web portal. I added a single new desired property and I noticed that the full content of the device twin is received by my test device (including all the other properties I have not changed). I would expect my device to receive a partial twin update containing only the modified property. Do I need to change settings on the web portal to send partial instead of full updates? Thanks!

Hello @Guillaume, welcome to this moderated Azure community forum. The behavior you experience, receiving the full set of desired properties even when only one is changed, is the default behavior and cannot be modified. The set of all desired properties must be seen as the complete desired state and must be handled as being 'atomic' (as in 'uncuttable'). The method used to handle desired property changes must be smart enough (or dump enough) to just process each separate desired property first. Only then, any action needed on any desired property change must be executed. If the response helped, do "Accept Answer". If it doesn't work, please let us know the progress. All community members with similar issues will benefit by doing so. Your contribution is highly appreciated.

Setting desired property in device twin sends the full content of the device twin instead of partial update

Accepted answer

Sander van de Velde | MVP 32,726 Reputation points MVP

2024-09-19T20:56:11.8433333+00:00

Hello @Guillaume,

welcome to this moderated Azure community forum.

The behavior you experience, receiving the full set of desired properties even when only one is changed, is the default behavior and cannot be modified.

The set of all desired properties must be seen as the complete desired state and must be handled as being 'atomic' (as in 'uncuttable').

The method used to handle desired property changes must be smart enough (or dump enough) to just process each separate desired property first. Only then, any action needed on any desired property change must be executed.

If the response helped, do "Accept Answer". If it doesn't work, please let us know the progress. All community members with similar issues will benefit by doing so. Your contribution is highly appreciated.
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Guillaume 25 Reputation points

2024-09-20T07:04:39.0733333+00:00

Hi @Sander van de Velde

Thank you for your answer.

In the docs here: https://github.com/MicrosoftDocs/azure-docs/blob/main/articles/iot-hub/iot-hub-devguide-device-twins.md#device-operations it says that "The device receives the same form of update (partial or full replacement) executed by the solution back end."

My understanding is that it is possible to send a partial update of the desired properties to a device, but this has to be done with the backend APIs. The web portal's default behaviour is to do full updates. Is that correct?

Thanks,

Guillaume

Sander van de Velde | MVP 32,726 Reputation points MVP

2024-09-20T21:47:43.33+00:00

Hello @Guillaume,

the short answer is that the code I use to listen to device twin (and module twin) changes just receives a twin object and then tries to read the specific properties. Thus the logic handles the received value as an atomic set of properties.

So, just test the desired properties update scenarios and let the device log what properties arrive.

The long answer is that we also work with (Azure IoT Edge related) layered deployments where we combine more generic layer-related properties with device-specific properties. Due to a bug in the layered deployments logic (the current solution does not follow the desired properties strategy for layered deployments), we for an extra read of the desired properties is some change is detected (either by changing device related properties or layered deployments related properties). We encountered a serious problem for a customer situation (loss of data on the edge) so that is why we for a complete read. By forcing a reread of all properties (even when a subset is sent) we have a save solution that works under every condition.
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