Fundamentals - Middleware - Factory-based middleware

In this article

• Activation per client request (injection of scoped services)

• Strong typing of middleware

IMiddleware

public class ConventionalMiddleware
{
    private readonly RequestDelegate _next;

    public ConventionalMiddleware(RequestDelegate next)
        => _next = next;

    public async Task InvokeAsync(HttpContext context, SampleDbContext dbContext)
    {
        var keyValue = context.Request.Query["key"];

        if (!string.IsNullOrWhiteSpace(keyValue))
        {
            dbContext.Requests.Add(new Request("Conventional", keyValue));

            await dbContext.SaveChangesAsync();
        }

        await _next(context);
    }
}

public class FactoryActivatedMiddleware : IMiddleware
{
    private readonly SampleDbContext _dbContext;

    public FactoryActivatedMiddleware(SampleDbContext dbContext)
        => _dbContext = dbContext;

    public async Task InvokeAsync(HttpContext context, RequestDelegate next)
    {
        var keyValue = context.Request.Query["key"];

        if (!string.IsNullOrWhiteSpace(keyValue))
        {
            _dbContext.Requests.Add(new Request("Factory", keyValue));

            await _dbContext.SaveChangesAsync();
        }

        await next(context);
    }
}

public static class MiddlewareExtensions
{
    public static IApplicationBuilder UseConventionalMiddleware(
        this IApplicationBuilder app)
        => app.UseMiddleware<ConventionalMiddleware>();

    public static IApplicationBuilder UseFactoryActivatedMiddleware(
        this IApplicationBuilder app)
        => app.UseMiddleware<FactoryActivatedMiddleware>();
}

public static IApplicationBuilder UseFactoryActivatedMiddleware(
    this IApplicationBuilder app, bool option)
{
    // Passing 'option' as an argument throws a NotSupportedException at runtime.
    return app.UseMiddleware<FactoryActivatedMiddleware>(option);
}

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddDbContext<SampleDbContext>
    (options => options.UseInMemoryDatabase("SampleDb"));

builder.Services.AddTransient<FactoryActivatedMiddleware>();

var app = builder.Build();

app.UseConventionalMiddleware();
app.UseFactoryActivatedMiddleware();

IMiddlewareFactory

Additional resources

• View or download sample code (how to download)

• ASP.NET Core Middleware

• Middleware activation with a third-party container in ASP.NET Core

Ref: Factory-based middleware activation in ASP.NET Core