Handling multiple return values in an Azure function

Question

I've got an Azure function that currently consumes messages from an Azure Service Bus, does some transformation and posts a message to an Azure Event Hub. However, I also want to post a message to an Azure Service Bus, different from the one I'm consuming from. Can this be achieved by using multiple return values?

[FunctionName("IntegrationFunction")]
[return: EventHub("%Transactions:EVH:Transactions:Hub%", Connection = "Transactions:EVH:Transactions")]
public Transaction Run(
    [ServiceBusTrigger(
        "%Transactions:SB:Transactions:ReceiveTopic%",
        "%Transactions:SB:Transactions:AnalyticsTopicSubscription%",
        Connection = "Transactions:SB:Transactions")]
    string mySbMsg,
    ILogger log)
{
    if (string.IsNullOrWhiteSpace(mySbMsg))
    {
        throw new ArgumentNullException(nameof(mySbMsg));
    }

    log.LogInformation($"Service bus topic trigger function processing message: {mySbMsg}");
    
    var retailTransaction = JsonConvert.DeserializeObject<RetailTransaction>(
        mySbMsg,
        JsonSerialisationUtils.SerialiserSettings);
    
    if (retailTransaction == null)
    {
        throw new JsonException("Deserialized transaction was null");
    }

    try
    {
        var transaction = retailTransaction.ToDto();
        log.LogInformation($"Transaction {transaction.TransactionNumber} processed.");
        return transaction;
    }
    catch (Exception e)
    {
        log.LogError(e, "Error mapping transaction.");
    }

    return null;
}

Answer 1

It is not feasible to use multiple return in azure function as mentioned in this github issue instead you can use CloudQueue or IAsyncCollector<T> object.

• I am using the below code to send the service bus message to Event hub as well as another service bus queue.

using System;
using System.Threading.Tasks;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Host;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;

namespace _78237298
{
    public class IntegrationFunction
    {
        [FunctionName("IntegrationFunction")]
        public async Task Run(
            [ServiceBusTrigger(
            "%Transactions:SB:Transactions:ReceiveTopic%", 
            "%Transactions:SB:Transactions:AnalyticsTopicSubscription%", 
            Connection = "Transactions:SB:Transactions")]
            string mySbMsg,
            [EventHub("%Transactions:EVH:Transactions:Hub%", Connection = "Transactions:EVH:Transactions")] IAsyncCollector<Transaction> outputEventHubMessages,
            [ServiceBus("%OtherServiceBus:QueueName%", Connection = "OtherServiceBus:ConnectionString")] IAsyncCollector<string> outputQueueMessages,
            ILogger log)
        {
            if (string.IsNullOrWhiteSpace(mySbMsg))
            {
                throw new ArgumentNullException(nameof(mySbMsg));
            }

            log.LogInformation($"Service bus topic trigger function processing message: {mySbMsg}");

            var retailTransaction = JsonConvert.DeserializeObject<RetailTransaction>(
                mySbMsg);

            if (retailTransaction == null)
            {
                throw new JsonException("Deserialized transaction was null");
            }

            try
            {
                var transaction = retailTransaction.ToDto();
                log.LogInformation($"Transaction {transaction.TransactionNumber} processed.");
                
                // Send to Event Hub
                await outputEventHubMessages.AddAsync(transaction);

                // Send to another Service Bus queue
                var anotherSbMsg = JsonConvert.SerializeObject(transaction);
                await outputQueueMessages.AddAsync(anotherSbMsg);
            }
            catch (Exception e)
            {
                log.LogError(e, "Error mapping transaction.");
            }

        }
    }

    public class RetailTransaction
    {
        public string TransactionNumber { get; set; }
        public decimal Amount { get; set; }

        public Transaction ToDto()
        {
            return new Transaction
            {
                TransactionNumber = this.TransactionNumber,
                Amount = this.Amount
            };
        }
    }

    public class Transaction
    {
        public string TransactionNumber { get; set; }
        public decimal Amount { get; set; }
    }
}

.csproj-

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <AzureFunctionsVersion>v4</AzureFunctionsVersion>
    <RootNamespace>_78237298</RootNamespace>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Azure.Messaging.EventHubs" Version="5.11.1" />
    <PackageReference Include="Microsoft.Azure.WebJobs.Extensions.EventHubs" Version="6.2.0" />
    <PackageReference Include="Microsoft.Azure.WebJobs.Extensions.ServiceBus" Version="5.14.0" />
    <PackageReference Include="Microsoft.NET.Sdk.Functions" Version="4.3.0" />
  </ItemGroup>
  <ItemGroup>
    <None Update="host.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Update="local.settings.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <CopyToPublishDirectory>Never</CopyToPublishDirectory>
    </None>
  </ItemGroup>
</Project>

Output-

1st Service Bus Topic-

I am sending message from this Service Bus.

Event Hub-

2nd Service Bus Queue-