DI in Azure Functions

Question

I have some class libraries that I use in my ASP.NET Web API app that handle all my backend stuff e.g. CRUD operations to multiple databases like Azure SQL Database, Cosmos

Answer 1

I have been using SimpleInjector perfectly fine in Azure Functions. Just create a class (let's call it IoCConfig) that has the registrations and make a static instance of that class in function class so that each instance will use the existing instance.

public interface IIoCConfig
{
    T GetInstance() where T : class;
}

public class IoCConfig : IIoCConfig
{
    internal Container Container;

    public IoCConfig(ExecutionContext executionContext, ILogger logger)
    {
        var configurationRoot = new ConfigurationBuilder()
            .SetBasePath(executionContext.FunctionAppDirectory)
            .AddJsonFile("local.settings.json", optional: true, reloadOnChange: true)
            .AddEnvironmentVariables()
            .Build();

        Container = new Container();
        Configure(configurationRoot, logger);
    }

    public IoCConfig(IConfigurationRoot configurationRoot, ILogger logger)
    {
        Container = new Container();
        Configure(configurationRoot, logger);
    }

    private void Configure(IConfigurationRoot configurationRoot, ILogger logger)
    {
        Container.RegisterInstance(typeof(IConfigurationRoot), configurationRoot);
        Container.Register();
    }

    public T GetInstance() where T : class
    {
        return Container.GetInstance();
    }
}

Then in root:

   public static class SomeFunction
{
    public static IIoCConfig IoCConfig;

    [FunctionName("SomeFunction")]
    public static async Task Run(
        [ServiceBusTrigger("some-topic", "%SUBSCRIPTION_NAME%", Connection = "AZURE_SERVICEBUS_CONNECTIONSTRING")]
        SomeEvent msg,
        ILogger log,
        ExecutionContext executionContext)
    {
        Ensure.That(msg).IsNotNull();

        if (IoCConfig == null)
        {
            IoCConfig = new IoCConfig(executionContext, log);
        }

        var someType = IoCConfig.GetInstance();
        await someType.Handle(msg);
    }
}