Dependency Injection with Azure Functions

I got bit by the dependency injection bug a few months ago and want to use it when I can, and it makes sense. Within a month or so of writing this post, Azure Functions started to support dependency injection in functions. It uses the .NET Core Dependency Injection system, so if you are used to that, this should mostly look familiar to you, except for what you have to do to wire up the Azure Functions SDK.

Getting Started

To get started, you need to add a reference to Microsoft.Azure.Functions.Extensions package in your Azure Functions project.

Install-Package Microsoft.Azure.Functions.Extensions -Version 1.0.0

Now you need a class to register your services. I use Startup to be consistent with ASP.NET Core. You can create whatever class name you want.

In that class, you need to inform the Azure Function SDK that this class is the startup class. To do this, add the assembly attribute FunctionsStartup to the class file.

[assembly: FunctionsStartup(typeof(Startup))]

This will require the following using statement.

using Microsoft.Azure.Functions.Extensions.DependencyInjection;

Have your class inherit from FunctionsStartup. Doing so requires your class to override the Configure method. The Configure method is where you register the services that you would like to inject. Since Azure Functions relies on the .NET Core Dependency Injection features, you can choose any supported service lifetimes.

using MyFunctions.Samples;
using Microsoft.Azure.Functions.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection.Extensions;

[assembly: FunctionsStartup(typeof(Startup))]
namespace MyFunctions.Samples
{
    public class Startup: FunctionsStartup
    {
        public override void Configure(IFunctionsHostBuilder builder)
        {
            builder.Services.TryAddSingleton<ISettings>(s => new Settings());
        }
    }
}

In this example, I am registering the ISettings class as a singleton class within the dependency injection system.

Now navigate to the class with your function.

NOTE You’ll have to remove the static modifier from the class and your function.

At this point, you can use directly inject the registered services.

private readonly ISettings _settings;

// Class Constructor
public MyFunctionApplication(ISettings settings)
{
    _settings = settings;
}

Then you can use _settings anywhere in your code. Like this example:

log.LogInformation($"Value from Settings class='{_settings.MySetting}'");

Wrap Up

That’s it. Pretty easy. I’ve included links to the Azure Function documentation and a sample repository that I used it below.

References

• Use dependency injection in .NET Azure Functions
• Sample code before Dependency Injection: Code
• Sample code after Dependency Injection: Code