Inject instance of ILogger in my component class Azure Functions using Autofac

user_6024969 0
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I am writing a simple Azure function.

I have installed the AzureFunctions.Autofac nuget package, and would like to use this as my DI library.

I have set up the following AutofacConfig class to register my types:

public class AutofacConfig
{
    public AutofacConfig(string functionName)
    {
        DependencyInjection.Initialize(builder =>
        {
            //do all of you initialization here

            //db client
            builder.RegisterType<EventComponent>()
            .As<IComponent<EventModel>>().SingleInstance(); 
        }, functionName);
    }
}

Here is my EventComponent class, to which I would like to inject the ILogger instance provided.

public class EventComponent : IComponent<EventModel>
{
    private ILogger _log;

    public EventComponent(ILogger logger)
    {
        _log = logger;
    }
}

Here is how I inject my EventComponent:

[FunctionName("AddEvent")]
    public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Function, "post", Route = null)]HttpRequestMessage req, ILogger log, [Inject]IComponent<EventModel> component)
    {
        log.LogInformation("C# HTTP trigger function processed a request.");

        await component.Add(new EventModel() { Id = Guid.NewGuid(), Description = $"Test description nr: {new Random().Next(1, 100000)}", User = "Test User" });

        return req.CreateResponse(HttpStatusCode.OK);
    }

The problem is, I get an exception on the above, because Autofac cannot resolve the parameter Microsoft.Extensions.Logging.ILogger.

Here is the exception message:

Exception binding parameter 'component'... Cannot resolve parameter 'Microsoft.Extensions.Logging.ILogger logger' of constructor 'Void .ctor(Microsoft.Extensions.Logging.ILogger)'. (See inner exception for details.) -> None of the constructors found with 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder' on type 'Event.Function.Components.EventComponent' can be invoked with the available services and parameters:\r\nCannot resolve parameter 'Microsoft.Extensions.Logging.ILogger logger' of constructor 'Void .ctor(Microsoft.Extensions.Logging.ILogger)'.",

How can I inject the ILogger instance into my EventComponent class?

autofac-configuration azure-functions autofac c#
3 Answers
user_27506950

I found your question when looking for the same thing. Have you found a solution?

Because I don't think that is possible. ILogger log is injected by the framework and I don't see how it could be referenced from your AutofacConfig-class.

How I resolved this was by changing the EventComponent-class to use Setter-injection instead of Constructor-injection, like this: 

public class EventComponent : IComponent<EventModel>
{
    public ILogger Log { get; set; }    
}

and change your function to set the Log-property:

[FunctionName("AddEvent")]
    public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Function, "post", Route = null)]HttpRequestMessage req, ILogger log, [Inject]IComponent<EventModel> component)
    {
        log.LogInformation("C# HTTP trigger function processed a request.");
        component.Log = log;
        await component.Add(new EventModel() { Id = Guid.NewGuid(), Description = $"Test description nr: {new Random().Next(1, 100000)}", User = "Test User" });

        return req.CreateResponse(HttpStatusCode.OK);
    }

The downside is that you need to remember to set that value at the start of every function that uses that class, but the injection works.

user_63854350

If you want to inject the ILogger into a function app you need to do the following:

  1. Add the correct log level and namespace to your host.json

     {
    "version": "2.0",
    "logging": {
         "applicationInsights": {
             "samplingSettings": {
                 "isEnabled": true
       }
     },
    "logLevel": {
        "YourNameSpace": "Information"
 }

  2. Inject ILogger<T> where T is your function app class name/type. In this sample my function app class name is Api.

     public class TestService : ITestService
 {
     private readonly ILogger<Api> _logger;

     public TestService(ILogger<Api> logger)
     {
         _logger = logger;
     }

     public void LogSomething(string message)
     {
         _logger.LogInformation(message);
     }
 }
user_22588430
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