How can I create a route constraint of type System.Guid?

Question

Can anyone point me in the right direction on how to map a route which requires two guids?

ie. http://blah.com/somecontroller/someaction/{firstGuid}/{secondGuid}

Answer 1

Create a RouteConstraint like the following:

public class GuidConstraint : IRouteConstraint {

public bool Match(HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection)
{
    if (values.ContainsKey(parameterName))
    {
        string stringValue = values[parameterName] as string;

        if (!string.IsNullOrEmpty(stringValue))
        {
            Guid guidValue;

            return Guid.TryParse(stringValue, out guidValue) && (guidValue != Guid.Empty);
        }
    }

    return false;
}}

Next when adding the route :

routes.MapRoute("doubleGuid", "{controller}/{action}/{guid1}/{guid2}", new { controller = "YourController", action = "YourAction" }, new { guid1 = new GuidConstraint(), guid2 = new GuidConstraint() });

Answer 2

If you use kazimanzurrashid's code, make sure to include Nikos D's comment. I ended up with this:

public class NonEmptyGuidRouteConstraint : IRouteConstraint
{
    public bool Match(HttpContextBase httpContext, Route route, 
        string parameterName, RouteValueDictionary values, RouteDirection routeDirection)
    {
        if (values.ContainsKey(parameterName))
        {
            var guid = values[parameterName] as Guid?;
            if (!guid.HasValue)
            {
                var stringValue = values[parameterName] as string;
                if (!string.IsNullOrWhiteSpace(stringValue))
                {
                    Guid parsedGuid;
                    Guid.TryParse(stringValue, out parsedGuid);
                    guid = parsedGuid;
                }
            }
            return (guid.HasValue && guid.Value != Guid.Empty);
        }
        return false;
    }
}

Answer 3

+1 @kazimanzurrashid. Seems spot on.

I'll give an alternative for those who haven't got C#4.0, of which Guid.TryParse is part of. There's another alternative with Regex but probably not worth the bother.

 public class GuidConstraint : IRouteConstraint
    {

        public bool Match(HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection)
        {
            if (values.ContainsKey(parameterName))
            {
                string stringValue = values[parameterName] as string;

                if (!string.IsNullOrEmpty(stringValue))
                {
                    //replace with Guid.TryParse when available.
                    try
                    {
                        Guid guid = new Guid(stringValue);
                        return true;
                    }
                    catch
                    {
                        return false;
                    }


                }
            }

            return false;
        }
    }

Answer 4

Definitely be wary of the code given by @kazimanzurrashid. It was a good start, but it definitely has a bug or too. I was passing a real Guid into the route values (instead of a string of a Guid), and I couldn't get anything to match my route. It took me forever to realize that the GuidConstraint was constraining against a real Guid, if that makes any sense. :)

Here's what I ended up with, which accepts any data type (not just string), is a bit faster (I think), and contains less if block nesting.

public class GuidConstraint : IRouteConstraint
{

    public bool Match(HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection)
    {
        object value;
        if (!values.TryGetValue(parameterName, out value)) return false;
        if (value is Guid) return true;

        var stringValue = Convert.ToString(value);
        if (string.IsNullOrWhiteSpace(stringValue)) return false;

        Guid guidValue;
        if (!Guid.TryParse(stringValue, out guidValue)) return false;
        if (guidValue == Guid.Empty) return false;

        return true;
    }
}

Answer 5

For MVC 5 there is already implemented the GuidRouteConstraint Class:
https://msdn.microsoft.com/en-us/library/system.web.mvc.routing.constraints.guidrouteconstraint(v=vs.118).aspx

Full list of available MVC constraints:
https://msdn.microsoft.com/en-us/library/system.web.mvc.routing.constraints(v=vs.118).

Answer 6

I found that assuming the type is a Guid causes issue when using things like @Html.RouteLink(...) and in Routing tests where the URL is supplied as a string. The code below caters for these situations. Using the above code samples caused issues in my views and/or tests, this below works fine.

 public class GuidConstraint : IRouteConstraint
{
    public bool Match(HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection)
    {
        var value = values[parameterName];
        if (value == null) return false;
        var stringValue = value.ToString();

        if (string.IsNullOrEmpty(stringValue)) return false;
        Guid guidValue;
        return Guid.TryParse(stringValue, out guidValue) && (guidValue != Guid.Empty);
    }
}