Configuring notification tag for Azure Function

Question

I'm using an Azure function to pick up messages from an event hub and send out notifications via the Azure notification hub. Works great! Now I wanted to see whether I could add tags to those messages in order to allow user targeting via those tags.

The output for the notification hub has a "tag expression" parameter which you can configure. But this seems to be a static text. I need to dynamically set these tags based on the message received from the event hub instead. I'm not sure whether you can somehow put dynamic content in there?

I also found that the constructor of the GcmNotification object that I'm using has an overload which allows a tag string to be used. But when I try that I get a warning on compile time stating this is deprecated and when the function fires it shows an error because the Tag property should be empty.

So I'm not clear on a) whether this is at all possible and b) how to do it when it is. Any ideas?

Update: as suggested I tried creating a POCO object to map to my input string. The string is as follows:

[{"deviceid":"repsaj-neptune-win10pi","readingtype":"temperature1","reading":22.031614503139451,"threshold":23.0,"time":"2016-06-22T09:38:54.1900000Z"}]

The POCO object:

public class RuleMessage
{
    public string deviceid;
    public string readingtype;
    public object reading;
    public double threshold;
    public DateTime time;
}

For the function I now tried both RuleMessage[] and List<RuleMessage> as parameter types, but the function complains it cannot convert the input:

2016-06-24T18:25:16.830 Exception while executing function: Functions.submerged-function-ruleout. Microsoft.Azure.WebJobs.Host: Exception binding parameter 'inputMessage'. Microsoft.Azure.WebJobs.Host: Binding parameters to complex objects (such as 'RuleMessage') uses Json.NET serialization. 1. Bind the parameter type as 'string' instead of 'RuleMessage' to get the raw values and avoid JSON deserialization, or 2. Change the queue payload to be valid json. The JSON parser failed: Cannot deserialize the current JSON array (e.g. [1,2,3]) into type 'Submission#0+RuleMessage' because the type requires a JSON object (e.g. {"name":"value"}) to deserialize correctly. To fix this error either change the JSON to a JSON object (e.g. {"name":"value"}) or change the deserialized type to an array or a type that implements a collection interface (e.g. ICollection, IList) like List that can be deserialized from a JSON array. JsonArrayAttribute can also be added to the type to force it to deserialize from a JSON array.

Function code:

using System;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using Microsoft.Azure.NotificationHubs;

public static void Run(List<RuleMessage> inputEventMessage, string inputBlob, out Notification notification, out string outputBlob, TraceWriter log)
{
    if (inputEventMessage == null || inputEventMessage.Count != 1)
    {
        log.Info($"The inputEventMessage array was null or didn't contain exactly one item.");

        notification = null;
        outputBlob = inputBlob;

        return;
    }

    log.Info($"C# Event Hub trigger function processed a message: {inputEventMessage[0]}"); 

    if (String.IsNullOrEmpty(inputBlob))
        inputBlob = DateTime.MinValue.ToString();

    DateTime lastEvent = DateTime.Parse(inputBlob);
    TimeSpan duration = DateTime.Now - lastEvent;

    if (duration.TotalMinutes >= 0) {
        notification = GetGcmMessage(inputMessage.First()); 
        log.Info($"Sending notification message: {notification.Body}");
        outputBlob = DateTime.Now.ToString();
    } 
    else {
        log.Info($"Not sending notification message because of timer ({(int)duration.TotalMinutes} minutes ago).");

        notification = null;
        outputBlob = inputBlob;
    }
}

private static Notification GetGcmMessage(RuleMessage input)
{
    string message;

    if (input.readingtype == "leakage")
        message = String.Format("[FUNCTION GCM] Leakage detected! Sensor {0} has detected a possible leak.", input.reading);
    else
        message = String.Format("[FUNCTION GCM] Sensor {0} is reading {1:0.0}, threshold is {2:0.0}.", input.readingtype, input.reading, input.threshold);

    message = "{\"data\":{\"message\":\""+message+"\"}}";

    return new GcmNotification(message);
}

public class RuleMessage
{
    public string deviceid;
    public string readingtype;
    public object reading;
    public double threshold;
    public DateTime time;
}

Update 28-6-2016: I've not managed to get it working by switching ASA output to line seperated to that it doesn't generate a JSON array any more. This is a temp. fix because the Function binding now fails as soon as there is more than one line in the output (which can happen).

Anyways, I now proceeded to set the tagExpression, as per instruction I changed it to:

{
  "type": "notificationHub",
  "name": "notification",
  "hubName": "repsaj-neptune-notifications",
  "connection": "repsaj-neptune-notifications_NOTIFICATIONHUB",
  "direction": "out",
  "tagExpression": "deviceId:{deviceid}"
}

Where {deviceid} equals the deviceid property on my RuleMessage POCO. Unfortunately this doesn't work, when I call the function it outputs:

Exception while executing function: Functions.submerged-function-ruleout. Microsoft.Azure.WebJobs.Host: Exception binding parameter 'notification'. Microsoft.Azure.WebJobs.Host: No value for named parameter 'deviceid'.

Which is not true, I know for sure the property has been set as I've logged it to the ouput window. I also tried something like {inputEventMessage.deviceid}, but that doesn't work either (as I didn't get how the runtime would map {deviceid} to the correct input object when there's more than one.

Answer 1

The tagExpression binding property supports binding parameters coming from trigger input properties. For example, assume your incoming Event Hub event has properties A and B. You can use these properties in your tagExpression using the parens syntax, e.g.: My Tag {A}-{B}.

In general, most of the properties across all the binding types support binding parameters in this way.