如何使用python IoT中心设备SDK从物联网设备中检索完整的设备孪生

Question

I'm writing an azure iot device application with the IoT Hub Device SDK in python.

I use the desired properties of the device twin state in my application and update them via the device_twin_callback() on device twin changes coming from azure. However, when I reprovision my device (eg on reboot), I get the initial device twin state specified in the DPS and not the current twin state of the IoT Hub.

Is there a way to retrieve the current device twin state on reprovisioning with the IoT Hub Device SDK in python?

One solution I would like to avoid is to save the last state of the device in a file.

Answer 1

Is there a way to retrieve the current device twin state on reprovisioning with the IoT Hub Device SDK in python?

Your question is not accuracy. There is not other ways to retrieve the current device twin state, only the REST API Service - Get Twin and its related Python API iothub_twin_method.get_twin .

The device twin included in device state data on reprovisioning is only depended on the choice of Reprovisioning policies , as below.

• Re-provision and migrate data : This policy is the default for new enrollment entries. This policy takes action when devices associated with the enrollment entry submit a new request (1). Depending on the enrollment entry configuration, the device may be reassigned to another IoT hub. If the device is changing IoT hubs, the device registration with the initial IoT hub will be removed. The updated device state information from that initial IoT hub will be migrated over to the new IoT hub (2). During migration, the device's status will be reported as Assigning.

• Re-provision and reset to initial config : This policy takes action when devices associated with the enrollment entry submit a new provisioning request (1). Depending on the enrollment entry configuration, the device may be reassigned to another IoT hub. If the device is changing IoT hubs, the device registration with the initial IoT hub will be removed. The initial configuration data that the provisioning service instance received when the device was provisioned is provided to the new IoT hub (2). During migration, the device's status will be reported as Assigning. This policy is often used for a factory reset without changing IoT hubs.

• Never re-provision : The device is never reassigned to a different hub. This policy is provided for managing backwards compatibility.

Using Azure IoT SDK for Python, the reprovisioning policy is set by the parameters update_hub_assignment and migrate_device_data of ReprovisionPolicy object, please see the explaination below.

 The behavior of the service when a device is re-provisioned to an IoT hub. All required parameters must be populated in order to send to Azure. :param update_hub_assignment: Required. When set to true (default), the Device Provisioning Service will evaluate the device's IoT Hub assignment and update it if necessary for any provisioning requests beyond the first from a given device. If set to false, the device will stay assigned to its current IoT hub. Default value: True . :type update_hub_assignment: bool :param migrate_device_data: Required. When set to true (default), the Device Provisioning Service will migrate the device's data (twin, device capabilities, and device ID) from one IoT hub to another during an IoT hub assignment update. If set to false, the Device Provisioning Service will reset the device's data to the initial desired configuration stored in the corresponding enrollment list. Default value: True . :type migrate_device_data: bool 

And the ReprovisionPolicy object is as a property initialized in the EnrollmentGroup or IndividualEnrollment object.

So please try to change the combination of parameters update_hub_assignment and migrate_device_data of ReprovisionPolicy to realize your needs. Otherwise, your workaround to cache the historial data is the only solution.