Azure device twin add new reported property - node.js

Question

I am following the azure device twin tutorial https://learn.microsoft.com/en-us/azure/iot-hub/iot-hub-csharp-node-twin-how-to-configure
I can make this work to update an existing reported property. What I am not sure about is how can I add a new reported property.
Specifically the code looks snippet looks like:
var currentTelemetryConfig = twin.properties.reported.telemetryConfig;
currentTelemetryConfig.pendingConfig =
twin.properties.desired.telemetryConfig;
currentTelemetryConfig.status = "Pending";
telemetryConfig: currentTelemetryConfig
var patch = {
telemetryConfig: currentTelemetryConfig
};
twin.properties.reported.update(patch, function(err) {
if (err) {
console.log(err);
} else {
console.log('success');
}
}
I can easily understand how this works for the existing property update (in this case the telemetryConfig) but what would it look like if the change I was trying to make was to a entirely new property?
How would it work if I decide at some point the I want a a new desired property called "favourite_colour" : "blue"?
In the azure backend I can add this but how do I dynamically build the var patch variable?
I tried this but it returned an error:
twin.properties.reported.update(twin.properties.desired, function(err) {
if (err) {
console.log('Could not report properties');
} else {
console.log('Success');
}
});
This is what my twin looks like:
"properties": {
"desired": {
"active": true,
"pws": "xyz",
"$metadata": {
"$lastUpdated": "2018-03-27T18:21:57.010036Z",
"$lastUpdatedVersion": 5,
"active": {
"$lastUpdated": "2018-03-27T18:21:57.010036Z",
"$lastUpdatedVersion": 5
},
"pws": {
"$lastUpdated": "2018-03-27T18:21:57.010036Z",
"$lastUpdatedVersion": 5
}
},
"$version": 5
},
"reported": {
"telemetryConfig": 6,
"$metadata": {
"$lastUpdated": "2018-03-27T18:56:05.2445399Z",
"telemetryConfig": {
"$lastUpdated": "2018-03-27T18:56:05.2445399Z"
}
},
"$version": 5
}
}
}

Answer 1

I'm guessing you want to:
Add new reported property on device side (favourite_colour)
I first recommend you to read this sample in GitHub.
Main this sample shows different way to listen for updates in twin on different level. The top most, where any update in device twin will trigger an event; or specific property (favourite_color).
I've edited the sample from the Microsoft document you provided to work with favorite_color.
'use strict';
var Client = require('azure-iot-device').Client;
var Protocol = require('azure-iot-device-mqtt').Mqtt;
var connectionString = '{iot hub connection string}';
var client = Client.fromConnectionString(connectionString, Protocol);
var initConfigChange = function(twin, patch) {
twin.properties.reported.update(patch, function(err) {
if (err) {
console.log('Could not report properties');
} else {
console.log('Reported pending config change: ' + JSON.stringify(patch));
setTimeout(function() {completeConfigChange(twin, patch);}, 30000);
}
});
}
var completeConfigChange = function(twin, patch) {
if (patch.telemetryConfig) {
// Same as Sample
} else if (patch.favourite_colour) {
var currentfavourite_colour = twin.properties.reported.favourite_colour;
currentfavourite_colour.color = currentfavourite_colour.pendingConfig.color;
currentfavourite_colour.status = "Success";
delete currentfavourite_colour.pendingConfig;
var patch = {
favourite_colour: currentfavourite_colour
};
patch.favourite_colour.pendingConfig = null;
}
twin.properties.reported.update(patch, function(err) {
if (err) {
console.error('Error reporting properties: ' + err);
} else {
console.log('Reported completed config change: ' + JSON.stringify(patch));
}
});
};
client.open(function(err) {
if (err) {
console.error('could not open IotHub client');
} else {
client.getTwin(function(err, twin) {
if (err) {
console.error('could not get twin');
} else {
console.log('retrieved device twin');
twin.properties.reported.favourite_colour = {
color: "green"
}
twin.on('properties.desired', function(desiredChange) {
console.log("received change: "+JSON.stringify(desiredChange));
if (desiredChange.telemetryConfig) {
// Same as sample
} else if (desiredChange.favourite_colour) {
var currentfavourite_colour = twin.properties.reported.favourite_colour;
currentfavourite_colour.pendingConfig = twin.properties.desired.favourite_colour;
currentfavourite_colour.status = "Pending Color";
var patch = {
favourite_colour: currentfavourite_colour
};
initConfigChange(twin, patch);
}
});
}
});
}
});
What I did was use a if else statement to check the reported property; as I mentioned there are other ways to do this, check the GitHub code I provided earlier. Once I have the matched reported property I can update the in the same way as the existing sample.