Dependency Injection for Azure Functions v2
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readme.md

Dependency Injection Extensions for Azure Functions v2

About

This repo contains binding extensions for dependency injection in Azure Function v2. Out of the box Microsoft.Extensions.DependencyInjection is used for dependency injection, but it is possible to use any IoC container that implements the IServiceProvider interface (for example Autofac).

How to configure

The dependency injection bindings are available as a nuget package. Once the package is added to function project, a WebJobsStartup is needed to register and configure the dependency injection bindings.

This is an example WebJobsStartup class

using ExampleFunction;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Willezone.Azure.WebJobs.Extensions.DependencyInjection;

[assembly: WebJobsStartup(typeof(Startup))]
namespace ExampleFunction
{
    internal class Startup : IWebJobsStartup
    {
        public void Configure(IWebJobsBuilder builder) =>
            builder.AddDependencyInjection(ConfigureServices);

        private void ConfigureServices(IServiceCollection services)
        {
            services.AddTransient<ITransientGreeter, Greeter>();
            services.AddScoped<IScopedGreeter, Greeter>();
            services.AddSingleton<ISingletonGreeter, Greeter>();
        }
    }

}

The nuget package contains two extension methods to register the dependency injection extensions.

AddDependencyInjection(this IWebJobsBuilder builder, Action<IServiceCollection> configureServices)

This configures the extension using the Microsoft.Extensions.DependencyInjection container. Services can be registered in the configureServices action.

AddDependencyInjection<TServiceProviderBuilder>(this IWebJobsBuilder builder) where TServiceProviderBuilder : IServiceProviderBuilder

This configures the extension to use what ever IoC container is returned from the Build method of the IServiceProviderBuilder implementation. It also gives access to other components, e.g. the configuration.

Example that uses Autofac

public class AutofacServiceProviderBuilder : IServiceProviderBuilder
{
    private readonly IConfiguration _configuration;

    public AutofacServiceProviderBuilder(IConfiguration configuration) => _configuration = configuration;

    public IServiceProvider Build()
    {
        Debug.WriteLine(_configuration["Setting"]); // Get a setting from the configuration.

        var services = new ServiceCollection();
        services.AddTransient<ITransientGreeter, Greeter>();
        services.AddScoped<IScopedGreeter, Greeter>();
        services.AddSingleton<ISingletonGreeter, Greeter>();

        var builder = new ContainerBuilder();
        builder.Populate(services); // Populate is needed to have support for scopes.

        return new AutofacServiceProvider(builder.Build());
    }
}

Using the extension

Once the extension is registered and configured dependencies can be injected using the Inject attribute on a function.

Example

[FunctionName("Greeter")]
public static IActionResult Run(
    [HttpTrigger(AuthorizationLevel.Function, "get")]HttpRequest req,
    [Inject]ITransientGreeter transientGreeter,
    [Inject]IScopedGreeter scopedGreeter,
    [Inject]ISingletonGreeter singletonGreeter,
    ILogger logger)
{
    logger.LogInformation("C# HTTP trigger function processed a request.");

    var result = String.Join(Environment.NewLine, new[] {
        $"Transient: {transientGreeter.Greet()}",
        $"Scoped: {scopedGreeter.Greet()}",
        $"Singleton: {singletonGreeter.Greet()}",
    });
    return new OkObjectResult(result);
}

Azure Deployment

Currently there is an issue when publishing your function application that the required extensions.json is not created correctly. The issue is discussed here. Luckily there is a workaround for this: Just copy the Directory.Build.targets file into your Azure Functions project, this will then create the correct extensions.json file.