enable-settings-object-as-di.md

Enable Settings object as Dependency Injection

Overview

If the business logic of your application relies heavily on the function app settings, it is recommended to inject the settings object as part of the Microsoft IoC container.

Register Settings object in StartUp class.

1. Make sure to add your local settings or function app settings as you would regularly do.

2. Create the settings class and add IConfiguration param into its constructor.

   using Microsoft.Extensions.Configuration;
   
   public class StreamingDataFlowSettings : `IStreamingDataFlowSettings`
   {
       public StreamingDataFlowSettings(IConfiguration config)
       {
           // extract setting values
           this.EventHubName = config.GetValue<string>("EVENT_HUB_NAME");
           this.StorageAccountContainer = config.GetValue<string>("STORAGE_ACCOUNT_CONTAINER");
           this.Timeout = config.GetValue<int>("TIMEOUT", 60);
   
           // throw exceptions if required fields are not met
           Guard.ThrowIfNull("EVENT_HUB_NAME", this.EventHubName);
           Guard.ThrowIfNull("STORAGE_ACCOUNT_CONTAINER", this.StorageAccountContainer);
       }
   
       public string EventHubName { get; private set; }
   
       public string StorageAccountContainer { get; private set; }
   
       public int Timeout { get; private set; }
   }

   You may use the Guard class to validate your input and notify if a required field is missing during runtime.

3. Register the settings class into the DI

   using Microsoft.Azure.Functions.StreamingDataFlow.Extensions;
   
   public class Startup : FunctionsStartup
   {
       public override void Configure(IFunctionsHostBuilder builder)
       {
           var settings = new StreamingDataFlowSettings(builder.GetContext().Configuration);
           builder.Services.AddSingleton<IStreamingDataFlowSettings>(settings);
           builder.Services.RegisterServices(builder.GetContext().Configuration);
       }
   }

4. You can now inject this dependency object into your service constructors. For example:

   [DependencyInjection(typeof(IIntegrationEventHandlerAsync<StreamingDataChanged>), ServiceType.Scoped, 1)]  
   public class StreamingDataChangedEventHandlerAsync : IIntegrationEventHandlerAsync<StreamingDataChanged>
   {
       public StreamingDataChangedEventHandlerAsync(
           IStreamingDataFlowSettings settings)
       {
           this.settings = settings;
       }
   
       public async Task Handle(StreamingDataChanged eventData)
       {
           // add business logic...
       }
   }