Constructor dependency injection for web jobs causes an error in 3.0.0-rc1

Repro steps

1. Add interface to be injected into the functions.
2. Add interface to the functions constructor.
3. Run the web job.

Expected behavior

Programme to run with the injected interface working.

Actual behavior

Webjob errors with “Object reference not set to an instance of an object”

Related information

Provide any related information Error

fail: Host.Results[0] Microsoft.Azure.WebJobs.Host.FunctionInvocationException: Exception while executing function: Functions.ProcessWorkItem_ServiceBus —> System.NullReferenceException: Object reference not set to an instance of an object. at lambda_method(Closure , Functions , Object[] ) at Microsoft.Azure.WebJobs.Host.Executors.VoidTaskMethodInvoker 2.InvokeAsync(TReflected instance, Object[] arguments) in azure-webjobs-sdk-3.0.0-rc1\azure-webjobs-sdk-3.0.0-rc1\src\Microsoft.Azure.WebJobs.Host\Executors\VoidTaskMethodInvoker.cs:line 20 at Microsoft.Azure.WebJobs.Host.Executors.FunctionInvoker 2.InvokeAsync(Object instance, Object[] arguments) in azure-webjobs-sdk-3.0.0-rc1\azure-webjobs-sdk-3.0.0-rc1\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionInvoker.cs:line 63 at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.InvokeAsync(IFunctionInvoker invoker, ParameterHelper parameterHelper, CancellationTokenSource timeoutTokenSource, CancellationTokenSource functionCancellationTokenSource, Boolean throwOnTimeout, TimeSpan timerInterval, IFunctionInstance instance) in azure-webjobs-sdk-3.0.0-rc1\azure-webjobs-sdk-3.0.0-rc1\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 562 at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ExecuteWithWatchersAsync(IFunctionInstance instance, ParameterHelper parameterHelper, ILogger logger, CancellationTokenSource functionCancellationTokenSource) in azure-webjobs-sdk-3.0.0-rc1\azure-webjobs-sdk-3.0.0-rc1\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 509 at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ExecuteWithLoggingAsync(IFunctionInstance instance, ParameterHelper parameterHelper, IFunctionOutputDefinition outputDefinition, ILogger logger, CancellationTokenSource functionCancellationTokenSource) in azure-webjobs-sdk-3.0.0-rc1\azure-webjobs-sdk-3.0.0-rc1\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 445 at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ExecuteWithLoggingAsync(IFunctionInstance instance, FunctionStartedMessage message, FunctionInstanceLogEntry instanceLogEntry, ParameterHelper parameterHelper, ILogger logger, CancellationToken cancellationToken) in azure-webjobs-sdk-3.0.0-rc1\azure-webjobs-sdk-3.0.0-rc1\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 249 — End of inner exception stack trace — at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ExecuteWithLoggingAsync(IFunctionInstance instance, FunctionStartedMessage message, FunctionInstanceLogEntry instanceLogEntry, ParameterHelper parameterHelper, ILogger logger, CancellationToken cancellationToken) in azure-webjobs-sdk-3.0.0-rc1\azure-webjobs-sdk-3.0.0-rc1\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 293 at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.TryExecuteAsync(IFunctionInstance functionInstance, CancellationToken cancellationToken) in azure-webjobs-sdk-3.0.0-rc1\azure-webjobs-sdk-3.0.0-rc1\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 89

Program.cs

public static async Task Main(string[] args)
{
    var builder = new HostBuilder()
        .UseEnvironment("Development")
        .ConfigureWebJobs(b =>
        {
            b.AddDashboardLogging()
            .AddAzureStorageCoreServices()
            .AddAzureStorage()
            .AddServiceBus()
            .AddEventHubs()
            .AddExecutionContextBinding();
        })
        .ConfigureAppConfiguration(b =>
        {
            // Adding command line as a configuration source
            b.AddCommandLine(args);
        })
        .ConfigureServices((hostContext, services) => {
            services.AddSingleton<IJobActivator>(new JobActivator(services.BuildServiceProvider()));
            services.AddScoped<Functions, Functions>();
            services.AddSingleton<IWriteText, WriteText>(); })
        .ConfigureLogging((context, b) =>
        {
            b.SetMinimumLevel(LogLevel.Debug);
            b.AddConsole();
            // If this key exists in any config, use it to enable App Insights
            string appInsightsKey = context.Configuration["APPINSIGHTS_INSTRUMENTATIONKEY"];
            if (!string.IsNullOrEmpty(appInsightsKey))
            {
                b.AddApplicationInsights(o => o.InstrumentationKey = appInsightsKey);
            }
        })
        .UseConsoleLifetime();

    var host = builder.Build();
    using (host)
    {
        await host.RunAsync();
    }
}

Functions.cs

public class Functions
{
    private readonly IWriteText _writeText;

    public Functions(IWriteText writeText)
    {
        _writeText = writeText;
    }

    public async Task ProcessWorkItem_ServiceBus(
        [ServiceBusTrigger("%queue%", Connection = "AzureWebJobsServiceBus")] string item, ILogger log)
    {
        log.LogInformation(_writeText.PopPop());
    }
}

IWriteText.cs

public interface IWriteText
{
    string PopPop();
}

public class WriteText : IWriteText
{
    public string PopPop()
    {
        return "Pop Pop!";
    }
}

[johnkwaters]

Amy news on first class DI support, and documentation?

[dotnetjunkie]

Hi @mathewc, @fabiocav’s change does indeed fix the problem. Wonder how I missed that. When implementing an IJobActicatorEx, the supplied IFunctionInstanceEx contains a IServiceProvider property, which is the actual scoped provider. This means that every DI Container should now be able to plugin to this model. Here’s the Simple Injector verion:

public class SimpleInjectorJobActivator : IJobActivatorEx
{
    private readonly Container container;

    public SimpleInjectorJobActivator(Container container) => this.container = container;

    public T CreateInstance<T>(IFunctionInstanceEx functionInstance)
    {
        var disposer = functionInstance.InstanceServices.GetRequiredService<ScopeDisposable>();
        this.disposer.Scope = AsyncScopedLifestyle.BeginScope(this.container);
        // Scopes in Simple Injector are ambient; you always resolve from the container
        return (T)this.container.GetInstance(typeof(T));
    }

    // Ensures a created Simple Injector scope is disposed at the end of the request
    public sealed class ScopeDisposable : IDisposable
    {
        public Scope Scope { get; set; }
        public void Dispose() => this.Scope?.Dispose();
    }
}

By using the following configuration, jobs can be resolved using Simple Injector:

services
    .AddScoped<SimpleInjectorJobActivator.ScopeDisposable>()
    .AddSingleton<IJobActivator>(new SimpleInjectorJobActivator(container));

Awesome work @fabiocav.