MultipleStartup.md - brainchildservices/curriculum GitHub Wiki

SLIDE-1

Multiple Startup

When the app defines separate Startup classes for different environments (for example, StartupDevelopment), the appropriate Startup class is selected at runtime. The class whose name suffix matches the current environment is prioritized. If the app is run in the Development environment and includes both a Startup class and a StartupDevelopment class, the StartupDevelopment class is used. For more information, see Use multiple environments.

See The host for more information on the host. For information on handling errors during startup, see Startup exception handling.

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The ConfigureServices method

The ConfigureServices method is:

• Optional.
• Called by the host before the Configure method to configure the app's services.
• Where configuration options are set by convention.

The host may configure some services before Startup methods are called. For more information, see The host.

For features that require substantial setup, there are Add{Service} extension methods on IServiceCollection. For example, AddDbContext, AddDefaultIdentity, AddEntityFrameworkStores, and AddRazorPages:

 public class Startup
 {
   public Startup(IConfiguration configuration)
   {
       Configuration = configuration;
   }

   public IConfiguration Configuration { get; }

   public void ConfigureServices(IServiceCollection services)
   {

       services.AddDbContext<ApplicationDbContext>(options =>
           options.UseSqlServer(
               Configuration.GetConnectionString("DefaultConnection")));
       services.AddDefaultIdentity<IdentityUser>(
          options => options.SignIn.RequireConfirmedAccount = true)
           .AddEntityFrameworkStores<ApplicationDbContext>();

       services.AddRazorPages();
   }

Adding services to the service container makes them available within the app and in the Configure method. The services are resolved via dependency injection or from ApplicationServices.

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The Configure method

The Configure method is used to specify how the app responds to HTTP requests. The request pipeline is configured by adding middleware components to an IApplicationBuilder instance. IApplicationBuilder is available to the Configure method, but it isn't registered in the service container. Hosting creates an IApplicationBuilder and passes it directly to Configure.

The ASP.NET Core templates configure the pipeline with support for:

• Developer Exception Page
• Exception handler
• HTTP Strict Transport Security (HSTS)
• HTTPS redirection
• Static files
• ASP.NET Core MVC and Razor Pages

SLIDE-3(DOWNWARDS)

 public class Startup
 {
     public Startup(IConfiguration configuration)
     {
         Configuration = configuration;
     }

     public IConfiguration Configuration { get; }

     public void ConfigureServices(IServiceCollection services)
     {
         services.AddRazorPages();
     }

     public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
     {
         if (env.IsDevelopment())
         {
             app.UseDeveloperExceptionPage();
         }
         else
         {
             app.UseExceptionHandler("/Error");
             app.UseHsts();
         }

         app.UseHttpsRedirection();
         app.UseStaticFiles();

         app.UseRouting();

         app.UseAuthorization();

         app.UseEndpoints(endpoints =>
         {
             endpoints.MapRazorPages();
         });
     }
   }

The preceding sample is for Razor Pages; the MVC version is similar.

Each Use extension method adds one or more middleware components to the request pipeline. For instance, UseStaticFiles configures middleware to serve static files.

Each middleware component in the request pipeline is responsible for invoking the next component in the pipeline or short-circuiting the chain, if appropriate.

Additional services, such as IWebHostEnvironment, ILoggerFactory, or anything defined in ConfigureServices, can be specified in the Configure method signature. These services are injected if they're available.

For more information on how to use IApplicationBuilder and the order of middleware processing, see ASP.NET Core Middleware.

Ref:- https://docs.microsoft.com/en-us/aspnet/core/fundamentals/startup?view=aspnetcore-5.0