How to get the route group prefix when using RouteGroupBuilder in ASP.NET Core 7 WebApi-CodePudding

The .NET v7 framework introduced the concept of Route Groups to group mapped endpoints together based on a common prefix in the path:

app.MapGroup("/public/todos").MapTodosApi();

Now, in order to return an absolute path for the Created response (i.e. to a POST request), I need that route path prefix inside the service. This usecase is even discussed in the official documentation:

Instead of using relative addresses for the Location header in the 201 Created result, it’s also possible to use GroupRouteBuilder.GroupPrefix to construct a root-relative address

However, the GroupRouteBuilder class does not exist. There is only a RouteGroupBuilder, but an instance of it has no member GroupPrefix. Any suggestions how to actually get the prefix?

CodePudding user response：

Looks like the GroupPrefix property was removed from RouteGroupBuilder (after name was changed). Here https://github.com/dotnet/aspnetcore/issues/41427 is a comment that says:

// It was too easy for this to get out of sync with RouteGroupContext.Prefix in real life given RouteGroupBuilder decorators.

To get the Prefix, you can bring in HttpContextAccesor:

builder.Services.AddHttpContextAccessor();

Then call GetEndpoint() on the HttpContext, convert result to RouteEndpoint, and look at the RoutePattern

app.MapGroup("/public/todos").MapTodosApi();

app.Run();

public class Todo
{
    public int Id { get; set; }
    public string? Title { get; set; }
    public bool IsComplete { get; set; }
}

public static class TodosApi
{
    public static RouteGroupBuilder MapTodosApi(this RouteGroupBuilder group)
    {
        group.MapPost("/", CreateTodo);
        return group;
    }

    public static async Task<Created<Todo>> CreateTodo(Todo todo, IHttpContextAccessor httpContext)
    {

        var endpoint = httpContext.HttpContext.GetEndpoint();
        var pattern = ((RouteEndpoint)endpoint).RoutePattern;
    
        return TypedResults.Created($"{todo.Id}", todo);
    }
}

CodePudding user response：

That document you linked - although being a preview one - mentions:

use GetPathByRouteValues or GetUriByRouteValues with a routeName for even more options.

The offical one about link generation is here.
It shows how to inject and use a LinkGenerator (which also contains above 2 mentioned methods) in combination with such a named route.

Endpoints can be given names in order to generate URLs to the endpoint. Using a named endpoint avoids having to hard code paths in an app

To apply this to the example you are referring to;
give a name to the route that retrieves a Todo item, and use that one when generating the created-at url.

var group = app.MapGroup("todos");
group
    .MapGet("/{id}", (int id) =>
    {                
        // ...
        return new Todo { Id = id };
    })
    .WithName("GetToDo");

group
    .MapPost("/", (Todo todo, LinkGenerator linkGenerator) =>
    {
        // ...
        var url = linkGenerator.GetPathByName("GetToDo", new { id = todo.Id });
        return TypedResults.Created(url, todo);
    });

The idea about using the group prefix when composing the created-at url will not suffice in case the pattern of the GET (get-item) endpoint has an extra segment, since that one will not be included. You'll end up with combining multiple hard coded string parts.

In case the get-todo-item endpoint from above example would have an additional extra segment - as shown in the example below - then the created-at url for ToDo item with id 123 must be

/todos/extra/123

Combining linkGenerator with a named route takes care of that.

group
    .MapGet("/extra/{id}", (int id) =>
    {                
        // ...
        return new Todo { Id = id };
    })
    .WithName("GetToDo");