URL pattern

A URL pattern connects a request path to an endpoint. ASP.NET Core routing compares the path—not the hostname or query string—with patterns registered for routes. A matching route sends the request to its endpoint; a pattern is conventionally written without a leading slash. section 13.1.2

Start with fixed segments. The pattern `capital/uk` matches `/capital/uk`, but not `/capital`, `/capital/europe/uk`, or `/name/uk`: the segments must match in number and content. In `Program.cs`, `app.MapGet("capital/uk", Capital.Endpoint)` also limits the route to GET requests. Use `MapPost`, `MapPut`, `MapDelete`, `MapMethods`, or `Map` when the HTTP-method requirement differs. section 13.1.4 section 13.1.2

Replace a fixed segment with a variable when the endpoint needs its value. `app.MapGet("capital/{country}", Capital.Endpoint)` matches paths such as `/capital/uk` and `/capital/france`; the endpoint can read `context.Request.RouteValues["country"]`. This avoids selecting an endpoint with routing and then parsing the path again inside it. Variable names cannot be `action`, `area`, `controller`, `handler`, or `page`. section 13.1.5

using Platform;

var builder = WebApplication.CreateBuilder(args);

var app = builder.Build();

app.MapGet("{first}/{second}/{third}", async context => {
    await context.Response.WriteAsync("Request Was Routed\n");
    foreach (var kvp in context.Request.RouteValues) {
        await context.Response
            .WriteAsync($"{kvp.Key}: {kvp.Value}\n");
    }
});

app.MapGet("capital/{country}", Capital.Endpoint);
app.MapGet("population/{city}", Population.Endpoint);

app.Run();

The `Program.cs` routes show named path segments feeding the capital and population endpoints; the three-segment route also prints the values routing extracted. section 13.1.5

Adjust the pattern when a simple one-variable-per-segment route is too narrow:

• `files/{filename}.{ext}` captures two values from one segment. The literal period separates them so routing can tell where one value ends. section 13.2.1
• `capital/{country=France}` supplies `France` when the second segment is absent: both `/capital` and `/capital/uk` match. section 13.2.2
• Optional segments and constraints can change which URLs match. For example, `{id:long?}` makes an `id` segment optional while requiring a supplied value to parse as a long. section 13.4 section 23.3.1

Patterns also work in Razor Pages. `@page "{id:long?}"` adds a segment variable to a page route; `@page "/lists/suppliers"` overrides the file-based route. To add a route without replacing an existing page route, configure `RazorPagesOptions` and call `Conventions.AddPageRoute("/Index", "/extra/page/{id:long?}")`. section 23.3.1 section 23.3.2

Test patterns with actual URLs, especially complex segments: some matching failures have changed between ASP.NET Core releases. Routes can also generate response URLs that target an endpoint, so matching is not their only use. section 13.2.1 section 13.4