Module twin coming back empty

Question

I am trying to set the desired properties on a Module's device twin, but when I retrieve the twin from the IoT Hub, it comes back full of nulls.

var moduleClient = ModuleClient.CreateFromConnectionString(connectionString);
var moduleTwin = await moduleClient.GetTwinAsync();

When I inspect moduleTwin in the debugger I get

The connection string is the one for the module, copied from the IoT Hub.

Any idea what I am doing wrong?

Answer 1

This is by design. So this issue is expected.

From module app, only has permission to read desired properties and read/write reported properties. See the following:

To access all module twin, you can do it from solution back end and require the ServiceConnect permission. Module twin is newly added. You need Microsoft.Azure.Devices V1.16.0-preview-001 or later. The following is a console app sample.

        RegistryManager registryManager = RegistryManager.CreateFromConnectionString(connectionString);
        Module module;

        var moduleTwin = await registryManager.GetTwinAsync(deviceID, moduleID);

Reference:

understand and use module twins in IoT Hub

"Get started with IoT Hub module identity and module twin using .NET back end and .NET device"