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Using helpers in Tridion Razor templating

Posted by Dominic Cronin at Nov 26, 2012 11:30 PM |

Today, for the first time, I used a helper in a Razor Tridion template. I'd made a fairly standard 'generic link' embedded schema, so that I could combine the possibility of a component link and an external link in a link list, and allow for custom link text. (Nothing to see here, move along now please.)  However, when I came to template the output, I wanted to have a function that would process an individual link. A feature of Razor templating is that you can define a @helper, which is a bit like a function, except that instead of a return value, the body is an exemplar of the required output. There is also support for functions, so to lift Alex Klock's own example:

@functions {
    public string HelloWorld(string name) {
        return "Hello " + name;


@helper HelloWorld(string name) {
    <div>Hello <em>@name</em>!</div>

will serve fairly similar purposes.

What I wanted to do today, however was slightly different; I didn't want to pass in a string, but a reference to my embedded field. All the examples on the web so far are about strings, and getting the types right proved interesting. I started out with some code like this:

@foreach(var link in @Fields.links){

So I needed a helper called RenderLink (OK - this might be a very trivial use-case, but a real problem all the same.). But what was the type of the argument? In theory, "links" is an EmbeddedSchemaField (or to give it it's full Sunday name: Tridion.ContentManager.ContentManagement.Fields.EmbeddedSchemaField) but what you get in practice is an object of type "Tridion.Extensions.Mediators.Razor.Models.DynamicItemFields". I'd already guessed this by poking around in the Razor Mediator sources, but after a few of my first experiments went astray, I ended up confirming that with @link.GetType().FullName

Well I tried writing a helper like this:

@using Tridion.Extensions.Mediators.Razor.Models 
@helper RenderLink(DynamicItemFields link){
... implementation

but that didn't work, because when you try to call the methods on 'link' they don't exist.

And then, just for fun, of course, I tried

@using Tridion.ContentManager.ContentManagement.Fields 
@helper RenderLink(EmbeddedSchemaField link){
... implementation

but that was just going off in an even worse direction. Yeah, sure, that type would have had the methods, but what I actually had hold of was a DynamicItemFields. Eventually, I remembered some hints in the mediator's documentation and tried using the 'dynamic' keyword. This, it turns out, is what you need. The 'dynamic' type lets you invoke methods at run-time without the compiler needing to know about them. (At last, I was starting to understand some of the details of the mediator's implementation!)

@helper RenderLink(dynamic link){
... implementation

This may be obvious with hindsight (as the old engineers' joke has it ... for some value of 'obvious') . For now, I'm writing another blog post tagged #babysteps and #notetoself, and enjoying my tendency to take the road less travelled.

TWO roads diverged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood

And looked down one as far as I could

To where it bent in the undergrowth;
Then took the other, as just as fair,
And having perhaps the better claim,

Because it was grassy and wanted wear;

Though as for that the passing there
Had worn them really about the same,
And both that morning equally lay

In leaves no step had trodden black.

Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.

I shall be telling this with a sigh

Somewhere ages and ages hence:
Two roads diverged in a wood, and I—
I took the one less traveled by,
And that has made all the difference.

-- Robert Frost