index.js

const { DefaultAzureCredential } = require("@azure/identity");
const { DigitalTwinsClient } = require("@azure/digital-twins-core");

module.exports = async function (context, req) {
    var digitalTwinId;
    var decodedPayload;
    
    // - UPDATE VARS BASED ON TTN V2/V3 UPLINK PAYLOAD
    if (req.body.dev_id && req.body.payload_fields){
        digitalTwinId = req.body.dev_id;
        decodedPayload = req.body.payload_fields;
    }else{
        digitalTwinId = req.body.end_device_ids.device_id;
        decodedPayload = req.body.uplink_message.decoded_payload;
    }
    
    // - AZURE_DIGITALTWINS_URL: The tenant ID in Azure Active Directory
    const url = process.env.AZURE_DIGITALTWINS_URL;
    
    const credential = new DefaultAzureCredential();
    // DefaultAzureCredential will automagically work in an Azure Function context if the Azure Function has
    // a system-assigned managed identity and has "Azure Digital Twins Data Owner" permission on the ADT instance
    const serviceClient = new DigitalTwinsClient(url, credential);
    
    var res;
    if(decodedPayload['$metadata'] && decodedPayload['$metadata']['$model']) {
        res = await serviceClient.upsertDigitalTwin(digitalTwinId, JSON.stringify(decodedPayload));
    } else {
        // TODO: it might be wise to retrieve the DTDL model of the device and only patch those properties
        // that actually exist in the model, instead of all the properties found in the incoming decoded payload
        
        const patches = [];
        Object.keys(decodedPayload).forEach(key => {
            if(!key.startsWith('$') && decodedPayload[key] != null) {
                patches.push({
                    op: 'add',
                    path: `/${key}`,
                    value: decodedPayload[key]
                })
            }
        });
        
        context.log(`Submitting the following patches to ${digitalTwinId}: `,patches)
        // try to update an existing twin with this ID, hoping it has a matching model ¯\_(ツ)_/¯
        res = await serviceClient.updateDigitalTwin(digitalTwinId, patches);
    }
    
    
    context.res = {
        // status: 200, /* Defaults to 200 */
        body: res
    };
}