asp.net-core Routing Routing constraints
Example
It is possible to create custom routing constraint which can be used inside routes to constraint a parameter to specific values or pattern.
This constrain will match a typical culture/locale pattern, like en-US, de-DE, zh-CHT, zh-Hant.
public class LocaleConstraint : IRouteConstraint
{
private static readonly Regex LocalePattern = new Regex(@"^[a-z]{2}(-[a-z]{2,4})?$",
RegexOptions.Compiled | RegexOptions.IgnoreCase);
public bool Match(HttpContext httpContext, IRouter route, string routeKey,
RouteValueDictionary values, RouteDirection routeDirection)
{
if (!values.ContainsKey(routeKey))
return false;
string locale = values[routeKey] as string;
if (string.IsNullOrWhiteSpace(locale))
return false;
return LocalePattern.IsMatch(locale);
}
}
Afterwards, the Constraint needs to be registered before it can be used in routes.
services.Configure<RouteOptions>(options =>
{
options.ConstraintMap.Add("locale", typeof(LocaleConstraint));
});
Now it can be used within routes.
Using it on Controllers
[Route("api/{culture:locale}/[controller]")]
public class ProductController : Controller { }
Using it on Actions
[HttpGet("api/{culture:locale}/[controller]/{productId}"]
public Task<IActionResult> GetProductAsync(string productId) { }
Using it in Default Routes
app.UseMvc(routes =>
{
routes.MapRoute(
name: "default",
template: "api/{culture:locale}/{controller}/{id?}");
routes.MapRoute(
name: "default",
template: "api/{controller}/{id?}");
});
