Lift Web Framework DRY dispatch

I have an Image class:

class Image extends LongKeyedMapper[Image] with IdPK with Logger {

which overrides toH开发者_高级运维tml method:

override def toHtml =
  <img src={"/gallery/image/%s/%s/%s/%s" format (slug.is, "fit", 100, 100)} />

and it works beacause of this:

def dispatch = {
    LiftRules.dispatch.append {
        case Req("gallery" :: "image" :: slug :: method :: width :: height :: Nil, _, _) => {
            () => Image.stream(slug, method, width, height)
        }
    }
}

As you can see this is not DRY approach, since you have to define the URL (/gallery/image) twice.

Is it possible to make it DRY? Can you get the path from LiftRules or something?

Thanks in advance, Etam.

This was answered by David Pollak on the lift list:

https://groups.google.com/d/topic/liftweb/VG0uOut9hb4/discussion

In short, you:

encapsulate the things in common (in this case, the path) in an object:

object ImageGallery {
  val path = "gallery" :: "image" :: Nil
  val pathLen = path.length
  def prefix = path.mkString("/", "/", "/")
}

create a custom unapply method that allows you to use the object in the pattern match in your dispatch method.

object ImageGallery {
  // ...
  def unapply(in: List[String]): Option[List[String]] = 
    Some(in.drop(pathLen)).filter(ignore => in.startsWith(path))
}

Your code is now:

<img src={ImageGallery.prefix+"%s/%s" ...}>

...and:

case Req(ImageGallery(slug :: method :: width :: height :: _), _, _) => // ...

See the message thread for more suggestions.