Overriding RouteValueDictionary in a Constraint in ASP.NET Core - asp.net-core

Question

I've just started using ASP.NET Core MVC and I want one route (global slug) to go to multiple controllers and actions depending on what type of page I'm serving to the user. For example, I want to use {*slug} for category and product pages.
I'm trying to override the default controller and action in a constraint.
In past versions of MVC, you could change either values["controller"] or values["action"] in a constraint and it would re-route to the appropriate controller and action.
public class Startup
{
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
app.UseMvc(routes =>
{
routes.MapRoute(
name: "Category",
template: "{*slug}",
defaults: new { controller = "Page", action = "Home" },
constraints: new { slug = new PageConstraint() }
);
});
}
}
public partial class PageConstraint : IRouteConstraint
{
public virtual bool Match(HttpContext httpContext, IRouter route, string routeKey, RouteValueDictionary values, RouteDirection routeDirection)
{
if (routeDirection == RouteDirection.UrlGeneration)
{
return true;
}
var slug = values["slug"] != null ? values["slug"].ToString() : null;
if (string.IsNullOrWhiteSpace(slug))
{
// Homepage
return true;
}
// Get category service
var categoryService = httpContext.RequestServices.GetRequiredService<ICategoryService>();
var category = categoryService.GetBySlug(slug);
if (category == null)
{
return false;
}
values["controller"] = "Category";
values["action"] = "Listing";
values["category"] = category;
return true;
}
}
In PageConstraint, I look to see if the Category exists, and if it does, it changes the Controller to Category and the Action to Listing in the RouteValueDictionary. However, when I debug the code through, it still goes to the Controller Page and the Action Home.
Anyone know why this is happening, or whether there is a better way of doing this? I know I could have one action in a controller doing all the work that the constraint is, but I would prefer to house the code in separate controllers and actions.

Answer 1

For your requirement, you could try to implement custom IRouter
public class RouterFromAppSettings : IRouter
{
private readonly IRouter _defaulRouter;
private readonly IConfiguration _config;
public RouterFromAppSettings(IRouter defaulRouter
, IConfiguration config)
{
_defaulRouter = defaulRouter;
_config = config;
}
public async Task RouteAsync(RouteContext context)
{
var controller = _config.GetSection("Router").GetValue<string>("Controller");
var action = _config.GetSection("Router").GetValue<string>("Action");
context.RouteData.Values["controller"] = controller;
context.RouteData.Values["action"] = action;
await _defaulRouter.RouteAsync(context);
}
public VirtualPathData GetVirtualPath(VirtualPathContext context)
{
return _defaulRouter.GetVirtualPath(context);
}
}
And then register it in Startup.cs like
app.UseMvc(routes =>
{
routes.Routes.Insert(0, new RouterFromAppSettings(routes.DefaultHandler,Configuration));
routes.MapRoute(
name: "default",
template: "{controller=Home}/{action=Index}/{id?}");
});