c8y_ModbusDevice of a child device is missing key 'type'

[zhongys-c8y]

A modbus child device added in the Modbus tab with a device protocol selected on the platform will have a fragment like:

"c8y_ModbusDevice": {
        "protocol": "TCP",
        "address": 8,
        "ipAddress": "172.17.0.1",
        "type": "/inventory/managedObjects/325530487"
    }

type includes the ID of the related device protocol. Without this info, the c8y Fieldbus device widget won't be able to select register/coil for creating operations.
When a tedge-modbus-plugin is running, the modbus child device managedObject will have following:

"c8y_ModbusDevice": {
        "protocol": "TCP",
        "address": 1,
        "port": 502,
        "ipAddress": "172.17.0.1"
    }

This will make the tedge-modbus-plugin can't work with the fieldbus device widget natively.

[reubenmiller]

@zhongys-c8y Do you know the c8y_ModbusDevice.type field is normally set? Since it include a managed object reference, does the device even receive this info?

[zhongys-c8y]

I found this function. Thin-edge device won't receive this from the platform, but it can overwrite the existing field of the child device MO.

[zhongys-c8y]

Need to correct myself. After creating the child device, an operation will be sent to the thin-edge device with c8y_ModbusDevice fragment, and it has the 'type' field.

[reubenmiller]

Ok, that sounds better. So the c8y_ModbusDevice handler will just have to be aware of the additional field and retain it somewhere so it doesn't get overridden when the modbus service republishes the related twin topic.