How to retrieve values from a context in Vapor?

Question

In Vapor, specifically in the class for a custom Leaf tag, how can you retrieve values stored in a context?

I'm trying to implement a tag that takes a string and a path, and renders a link unless the path is the current page, so, for example, #navElement("About Us", "/about") will produce a link to the site's about page on every page except the about page itself. On that page, it should display the text without a link on it.

I don't want to have to pass the current path to the tag every time I use it, so I've stored the request's path in the context, roughly like this (checks omitted):

drop.get(":page"){ request in
  return try drop.view.make(thePage, ["path": request.uri.path])
}

I can use #(path) in a template and see the path I expect.

My custom tag is derived from Tag, and its run method receives the context as an argument, and I can see the stored value in there in the debugger – but how do I get at it? The get method in the Context class, which seems to do this, is internal, so I can't use it. There is a comment that says subscripts are to be done, and I assume that this will ultimately be the way to extract values from the context, but in the meantime, is there any way to retrieve them?

tobygriffin · Accepted Answer · 2016-11-08T21:56:48.060

Just make the current path one of the arguments to your tag.

Droplet route:

drop.get(":page") { request in
  return try drop.view.make(thePage, ["currentPath": request.uri.path])
}

In template:

#navElement("About Us", "/about", currentPath)

Tag:

class NavElement: Tag {

  let name = "navElement"

  public func run(stem: Stem, context: LeafContext, tagTemplate: TagTemplate, arguments: [Argument]) throws -> Node? {
    guard
      let linkText = arguments[0].value?.string,
      let linkPath = arguments[1].value?.string,
      let currentPath = arguments[2].value?.string
    else { return nil }
    if linkPath == currentPath {
      return Node("We are at \(currentPath)")
    } else {
      return Node("Link \(linkText) to \(linkPath)")
    }
  }

}

Edit:

I have spoken to the developers of Vapor, and they do not intend to open up access to Context's contents publicly. However, since the queue: List<Node>() is public, you can just copy the get() function into your own extension and then you'll be able to do as you wanted.

Thanks, but I'm trying to avoid repeating that argument every time I use the tag, and since I have the context in the `run` method already, I was hoping to be able to extract the path from there. — MacAvon, Nov 08 '16 at 09:50
Thanks for finding this out. Seems like an odd decision, when they are passing the context to `run`, but mine not to reason why. The suggested workaround does the trick for me. — MacAvon, Nov 09 '16 at 13:47

How to retrieve values from a context in Vapor?

1 Answers1