Custom Route Constraints

You can create custom route constraints by implementing the IHttpRouteConstraint interface. For example, the following constraint restricts a parameter to a non-zero integer value.

public class NonZeroConstraint : IHttpRouteConstraint { public bool Match(HttpRequestMessage request, IHttpRoute route, string parameterName, IDictionary
    
      values, HttpRouteDirection routeDirection) { object value; if (values.TryGetValue(parameterName, out value) && value != null) { long longValue; if (value is long) { longValue = (long)value; return longValue != 0; } string valueString = Convert.ToString(value, CultureInfo.InvariantCulture); if (Int64.TryParse(valueString, NumberStyles.Integer, CultureInfo.InvariantCulture, out longValue)) { return longValue != 0; } } return false; } }
    

The following code shows how to register the constraint:

public static class WebApiConfig { public static void Register(HttpConfiguration config) { var constraintResolver = new DefaultInlineConstraintResolver(); constraintResolver.ConstraintMap.Add("nonzero", typeof(NonZeroConstraint)); config.MapHttpAttributeRoutes(constraintResolver); } }

Now you can apply the constraint in your routes:

[Route("{id:nonzero}")] public HttpResponseMessage GetNonZero(int id) { ... }

You can also replace the entire DefaultInlineConstraintResolver class by implementing the IInlineConstraintResolver interface. Doing so will replace all of the built-in constraints, unless your implementation of IInlineConstraintResolver specifically adds them.