Startup classes

Startup classes add functionality to Nucleus during startup, by providing an interface which extensions use to add classes to the dependency injection container. Use Startup classes to:

• Register an extension's Data Provider.
• Register an Event Handler.
• Register Nucleus Search Providers, Search Content Providers and Search Index Managers.
• Add other services to dependency injection, like adding a Filter.

Extensions can execute code during startup. In order to create a startup class, your assembly must have a HostingStartup attribute and must contain a class which implements the IHostingStartup interface.

The HostingStartup attribute and IHostingStartup interface are a standard part of ASP.NET core. Refer to Use hosting startup assemblies in ASP.NET Core for more information. The only difference in Nucleus is that all assemblies in extension folders which have a HostingStartup attribute are automatically added during startup, and do not need to be configured using the WebHostDefaults.HostingStartupAssembliesKey configuration key.

Your IHostingStartup implementation is run before Nucleus adds any services to dependency injection. You can execute code in a startup class which will prevent Nucleus from starting successfully, so take care if you are doing anything that isn't documented as a standard activity in a startup class. In general, you will add a delegate for configuring additional services by calling IWebHostBuilder.ConfigureServices.

Don't add a call to IWebHostBuilder.Configure - this does not add a delegate (additional code to execute during startup), it completely replaces the Nucleus .Configure code and will stop Nucleus from successfully starting.

This code is from the Elastic Search extension (source code). It adds a search index manager and search provider.

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Nucleus.Abstractions.Search;

[assembly: HostingStartup(typeof(Nucleus.Extensions.ElasticSearch.Startup))]

namespace Nucleus.Extensions.ElasticSearch;

public class Startup : IHostingStartup
{
  public void Configure(IWebHostBuilder builder)
  {
    builder.ConfigureServices((context, services) =>
    {
      services.AddTransient<ISearchIndexManager, SearchIndexManager>();
      services.AddTransient<ISearchProvider, SearchProvider>();
    });
  }
}

This code is from the Accept Terms module (source code). It adds the module's manager class and data provider classes to dependency injection.

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Nucleus.Data.EntityFramework;
using Nucleus.Modules.AcceptTerms.DataProviders;

[assembly: HostingStartup(typeof(Nucleus.Modules.AcceptTerms.Startup))]

namespace Nucleus.Modules.AcceptTerms;

public class Startup : IHostingStartup
{
  public void Configure(IWebHostBuilder builder)
  {
    builder.ConfigureServices((context, services) =>
    {
      services.AddSingleton<AcceptTermsManager>();
      services.AddDataProvider<IAcceptTermsDataProvider, DataProviders.AcceptTermsDataProvider, DataProviders.AcceptTermsDbContext>(context.Configuration);
    });
  }
}