Tutorial: Write a C# user-defined function for Azure Stream Analytics job (Preview)


.Net Standard user-defined functions for Azure Stream Analytics will be retired on 30th September 2024. After that date, it will not be possible to use the feature. Please transition to JavaScript user-defined functions for Azure Stream Analytics.

C# user-defined functions (UDFs) created in Visual Studio allow you to extend the Azure Stream Analytics query language with your own functions. You can reuse existing code (including DLLs) and use mathematical or complex logic with C#. There are three ways to implement UDFs:

  • CodeBehind files in a Stream Analytics project
  • UDFs from a local C# project
  • UDFs from an existing package from a storage account.

This tutorial uses the CodeBehind method to implement a basic C# function. The UDF feature for Stream Analytics jobs is currently in preview and shouldn't be used in production workloads.

In this tutorial, you learn how to:

  • Create a C# user defined function using CodeBehind.
  • Test your Stream Analytics job locally.
  • Publish your job to Azure.


Before you start, make sure you've completed the following prerequisites:

Create a container in your Azure Storage Account

The container you create is used to store the compiled C# package. If you create an Edge job, this storage account is also used to deploy the package to your IoT Edge device. Use a dedicated container for each Stream Analytics job. Reusing the same container for multiple Stream Analytics Edge jobs isn't supported. If you already have a storage account with existing containers, you may use them. If not, you need to create a new container.

Create a Stream Analytics project in Visual Studio

  1. Start Visual Studio.

  2. Select File > New > Project.

  3. In the templates list on the left, select Stream Analytics, and then select Azure Stream Analytics Edge Application or Azure Stream Analytics Application.

  4. Input the project Name, Location, and Solution name, and select OK.

    Create an Azure Stream Analytics Edge project in Visual Studio

Configure assembly package path

  1. Open Visual Studio and navigate to the Solution Explorer.

  2. Double-click the job configuration file, JobConfig.json.

  3. Expand the User-Defined Code Configuration section, and fill out the configuration with the following suggested values:

    Setting Suggested Value
    Global Storage Settings Resource Choose data source from current account
    Global Storage Settings Subscription < your subscription >
    Global Storage Settings Storage Account < your storage account >
    Custom Code Storage Settings Resource Choose data source from current account
    Custom Code Storage Settings Storage Account < your storage account >
    Custom Code Storage Settings Container < your storage container >

Write a C# UDF with CodeBehind

A CodeBehind file is a C# file associated with a single ASA query script. Visual Studio tools automatically zips the CodeBehind file and upload it to your Azure storage account upon submission. All classes must be defined as public and all objects must be defined as static public.

  1. In Solution Explorer, expand Script.asql to find the Script.asaql.cs CodeBehind file.

  2. Replace the code with the following sample:

        using System; 
        using System.Collections.Generic; 
        using System.IO; 
        using System.Linq; 
        using System.Text; 
        namespace ASAEdgeUDFDemo 
            public class Class1 
                // Public static function 
                public static Int64 SquareFunction(Int64 a) 
                    return a * a; 

Implement the UDF

  1. In Solution Explorer, open the Script.asaql file.

  2. Replace the existing query with the following query:

        SELECT machine.temperature, udf.ASAEdgeUDFDemo_Class1_SquareFunction(try_cast(machine.temperature as bigint))
        INTO Output
        FROM Input 

Local testing

  1. Download the temperature simulator sample data file.

  2. In Solution Explorer, expand Inputs, right-click Input.json, and select Add Local Input.

    Add local input to Stream Analytics job in Visual Studio

  3. Specify the local input file path for the sample data you downloaded and Save.

    Local input configuration for Stream Analytics job in Visual Studio

  4. Click Run Locally in the script editor. Once the local run has successfully saved the output results, press any key to see the results in table format.

    Run Azure Stream Analytics job locally with Visual Studio

  5. You can also select Open Results Folder to see the raw files in JSON and CSV format.

    View results of local Azure Stream Analytics job with Visual Studio

Debug a UDF

You can debug your C# UDF locally the same way you debug standard C# code.

  1. Add breakpoints in your C# function.

    Add breakpoints to Stream Analytics user-defined function in Visual Studio

  2. Press F5 to start debugging. The program stops at your breakpoints as expected.

    View Stream Analytics user-defined function debugging results

Publish your job to Azure

Once you've tested your query locally, select Submit to Azure in the script editor to publish the job to Azure.

Submit your Stream Analytics Edge job to Azure from Visual Studio

Deploy to IoT Edge devices

If you chose to build a Stream Analytics Edge job, it can now be deployed as an IoT Edge module. Follow the IoT Edge quickstart to create an IoT Hub, register an IoT Edge device, and install and start the IoT Edge runtime on your device. Then follow the deploy the job tutorial to deploy your Stream Analytics job as an IoT Edge module.

Next steps

In this tutorial, you created a simple C# user-defined function using CodeBehind, published your job to Azure, and deployed the job to Azure or IoT Edge device.

To learn more about the different ways to use C# user-defined functions for Stream Analytics jobs, continue to this article: