C# DOTNET Dependency Injection Order Clarification

March 11, 2024

I do not get the behaviour of DI in the following case.

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using System;
using Microsoft.Extensions.Azure;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Azure.Identity;

namespace TestResults.Processor;


internal class Program
{

    private static async Task Main(string[] args)
    {
        var configuration = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json", false, true)
            .AddEnvironmentVariables()
            .Build();

        var services = new ServiceCollection();
       

        services.AddLogging(configure =>
        {
            configure.AddConfiguration(configuration.GetSection("Logging"));
            configure.AddConsole();
        });

        services.ConfigureAndInjectServices(configuration);

        using var serviceProvider = services.BuildServiceProvider();

        var logger = serviceProvider.GetRequiredService<ILogger<Program>>();
        logger.LogInformation($"serviceBusFqns: ....");
        logger.LogInformation($"serviceBusFqns: ....");

    }

   
}

public static class DependencyInjectionHelper
{
    public static void ConfigureAndInjectServices(this IServiceCollection services, IConfigurationRoot configuration)
    {

        var serviceBusFqns = configuration.GetValue<string>("ServiceBus:FullyQualifiedNs");
        var managedIdentityClientID = configuration.GetValue<string>("ServiceBus:ManagedIdentityClientID");

        services.AddAzureClients(builder =>
        {
            builder.AddServiceBusClientWithNamespace(serviceBusFqns);
            builder.UseCredential(new DefaultAzureCredential());
        });

    }
}

I am able to see the logs produced on Console. But if I swap the order of these lines:

services.ConfigureAndInjectServices(configuration);

services.AddLogging(configure =>
{
    configure.AddConfiguration(configuration.GetSection("Logging"));
    configure.AddConsole();
});

the log does not log anymore (to Console). Why?

>Solution :

I think this happens due to the following:

AddAzureClientsCore which is invoked by AddAzureClients tries to register NullLoggerFactory as ILoggerFactory:

collection.TryAddSingleton<ILoggerFactory, NullLoggerFactory>();

While AddLogging will try to add add LoggerFactory as one:

services.TryAdd(ServiceDescriptor.Singleton<ILoggerFactory, LoggerFactory>());

TryAdd{...} methods will add the registration only if the service type hasn’t already been registered so the first one called wins (unlike with the Add{...} methods which will result in the last one wins).