ASP.NET MVC 3 Route Constraint : Regular Expression for not null

Question

I am trying to create a route constraint but not sure what would be the best for this. Here is the route with no constraint :

context.MapRoute(
    "Accommodation_accomm_tags",
    "accomm/{controller}/{action}/{tag}",
    new { action = "Tags", controller = "AccommProperty" },
    new { tag = @"" } //Here I would like to put a RegEx for not null match
);

What would be the best solution for this?

Matthew Abbott · Accepted Answer · 2011-09-21 10:46:28Z

8

Could you create an IRouteConstraint:

public class NotNullRouteConstraint : IRouteConstraint
{
  public bool Match(
    HttpContextBase httpContext, Route route, string parameterName, 
    RouteValueDictionary values, RouteDirection routeDirection)
  {
    return (values[parameterName] != null);
  }
}

Which you can wire up:

context.MapRoute(
  "Accommodation_accomm_tags",
  "accomm/{controller}/{action}/{tag}",
  new { action = "Tags", controller = "AccommProperty" },
  new { tag = new NotNullRouteConstraint() }
);

answered Sep 21, 2011 at 10:46

Matthew Abbott

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1 Comment

tugberk Over a year ago

I thought that too and this will be the solution if I cannot find a RegEx for not null. Thanks !

Darin Dimitrov · Accepted Answer · 2011-09-21 14:14:05Z

6

Why do you need a constraint for a not null/empty match? Normally if you define your route like this:

context.MapRoute(
    "Accommodation_accomm_tags",
    "accomm/{controller}/{action}/{tag}",
    new { action = "Tags", controller = "AccommProperty" },
);

and tag is not specified in the request url this route simply won't match.

And if you want a token to be optional, then:

context.MapRoute(
    "Accommodation_accomm_tags",
    "accomm/{controller}/{action}/{tag}",
    new { action = "Tags", controller = "AccommProperty", tag = UrlParameter.Optional },
);

Constraints are used when you want to constrain the value of a given route token to some specific format.

answered Sep 21, 2011 at 14:14

Darin Dimitrov

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2 Comments

tugberk Over a year ago

You nailed it again. I was trying to remember that there should be a some easy way for that but I couldn't. now it is clear. Thanks!

Vokinneberg Over a year ago

What if your action waiting for string parameter? In this case, if you'll specify tag as optional parameter it will contain null value.

Cymen · Accepted Answer · 2011-09-21 14:08:23Z

2

At first, I tried to create a RegEx for empty string which is ^$ (which is what null would be). However, it doesn't look like route constraints can be !=. How about matching one or more character with ^.+$?

So:

tag = @"^.+$"

edited Sep 21, 2011 at 14:08

answered Sep 21, 2011 at 14:02

Cymen

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5 Comments

tugberk Over a year ago

you have two sentences which are totally opposite to each other : I believe you want a RegEx for empty string... and ...you want not empty string of course...

Cymen Over a year ago

Well he asks for a RegExp for null which is actually empty string but he wants the opposite of that for the route constraint.

tugberk Over a year ago

I clearly pointed out that I need a RegEx for not null string. you can see it as comment inside my code sample : //Here I would like to put a RegEx for not null match I didn't ask for null match RegEx anywhere. Sorry but appreciate your effort though.

tugberk Over a year ago

@bzlm it wasn't there. see the update history : stackoverflow.com/posts/7501141/revisions

tugberk Over a year ago

@Cymen he he :) thanks, gonna give it a try. (don't hit the coffee hard though, not so healthy. you know what I mean :))

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