.NET7之MiniAPI(特别篇)：.NET7 Preview3

　　.NET7的第三个预览版发布了，同样带来了mini api的更新，这次带来了路由过滤器，与mvc版的action 过滤器相似。具体见https://devblogs.microsoft.com/dotnet/asp-net-core-updates-in-dotnet-7-preview-3/

　　用官方的代码，跑不起来，这样那样的问题，比如下面的代码，直接报空引用的异常。

app.MapGet("/data0/{no}", (string no) =>
{
    Console.WriteLine($"Get方法中：no={no}");
    return new Data { No = no, Name = "test" + DateTime.Now };

}).AddFilter((RouteHandlerInvocationContext context, RouteHandlerFilterDelegate next) =>
    {
        var no = (string?)context.Parameters[0];
        Console.WriteLine($"Get方法前：no={no}");
        if (no != null && !no.StartsWith("NO"))
        {
            return new ValueTask<object?>("no is error!");
        }
        var result = next(context);
        if (result.IsCompleted)
        {
            Console.WriteLine($"Get方法后：结果={result.Result}");
        }
        return result;
    });

　　经过一阵折腾，终于正常的跑了起来，需要把map的方法独立出来写才可以。同时这里使用了三种方式来使用过滤器，换汤不换药，本质一样。

var builder = WebApplication.CreateBuilder(args);

var app = builder.Build();

Data GetData(string no)
{
    Console.WriteLine($"Get方法中：no={no}");
    return new Data { No = no, Name = "test" + DateTime.Now };
};
//第一种方式
app.MapGet("/data1/{no}", GetData)
    .AddFilter((RouteHandlerInvocationContext context, RouteHandlerFilterDelegate next) =>
    {
        var no = (string?)context.Parameters[0];
        Console.WriteLine($"Get方法前：no={no}");
        if (no != null && !no.StartsWith("NO"))
        {
            return new ValueTask<object?>("no is error!");
        }
        var result = next(context);
        if (result.IsCompleted)
        {
            Console.WriteLine($"Get方法后：结果={result.Result}");
        }
        return result;
    });

string AddTest(Data data)
{
    Console.WriteLine($"Post方法中：no={data.No}");
    return "OK";
}
app.MapPost("/data1", AddTest)
    .AddFilter((RouteHandlerInvocationContext context, RouteHandlerFilterDelegate next) =>
    {
        var data = (Data?)context.Parameters[0];
        Console.WriteLine($"Post方法前：data={data}");
        var result = next(context);
        if (result.IsCompleted)
        {
            Console.WriteLine($"Post方法后：结果={result.Result}");
        }
        return result;
    });
//第二种方式
app.MapGet("/data2/{no}", GetData)
.AddFilter((RouteHandlerContext routeHandlerContext, RouteHandlerFilterDelegate next) =>
{
    return (context) =>
    {
        var no = (string?)context.Parameters[0];
        if (no != null && !no.StartsWith("NO"))
        {
            return new ValueTask<object?>("no is error!");
        }
        return next(context);
    };
});
//第三种方式
app.MapGet("/data3/{name}", GetData).AddFilter<MyFilter>();

app.Run();

public class MyFilter : IRouteHandlerFilter
{
    public ValueTask<object?> InvokeAsync(RouteHandlerInvocationContext context, RouteHandlerFilterDelegate next)
    {
        var no = (string?)context.Parameters[0];
        if (no != null && !no.StartsWith("NO"))
        {
            return new ValueTask<object?>("no is error!");
        }
        return next(context);
    }
}

public record Data
{
    public string No { get; set; }
    public string Name { get; set; }
}