Using the Razor view engine in a different way

Question

I thought it would be interesting if I could use the new MVC Razor View engine as a mail merge technology. It can still be part of an MVC website and does not have to be st

Answer 1

Warning

This is some ugly ugly code that was hacked together without testing it other than getting it to work properly.

VirtualPathProvider

Since we're not dealing with actual views on the server we have to add our own path provider to tell MVC where to get our dynamically generated templates. There should be more tests like checking the strings Dictionary to see if the view has been added.

public class StringPathProvider : VirtualPathProvider {
    public StringPathProvider()
        : base() {
    }

    public override CacheDependency GetCacheDependency(string virtualPath, IEnumerable virtualPathDependencies, DateTime utcStart) {
        return null;
    }

    public override bool FileExists(string virtualPath) {
        if (virtualPath.StartsWith("/stringviews") || virtualPath.StartsWith("~/stringviews"))
            return true;

        return base.FileExists(virtualPath);
    }

    public override VirtualFile GetFile(string virtualPath) {
        if (virtualPath.StartsWith("/stringviews") || virtualPath.StartsWith("~/stringviews"))
            return new StringVirtualFile(virtualPath);

        return base.GetFile(virtualPath);
    }

    public class StringVirtualFile : System.Web.Hosting.VirtualFile {

        string path;

        public StringVirtualFile(string path)
            : base(path) {
            //deal with this later
                this.path = path;
        }

        public override System.IO.Stream Open() {
            return new System.IO.MemoryStream(System.Text.ASCIIEncoding.ASCII.GetBytes(RazorViewEngineRender.strings[System.IO.Path.GetFileName(path)]));
        }
    }
}

Render Class

This class takes your template as a constructor parameter and adds it to a static Dictionary that is then read by the VirtualPathProvider above. You then call Render and you can optionally pass in a model. This will add the fully qualified model type to the @inherits and prepend that to the file contents.

public class RazorViewEngineRender {
    internal static Dictionary<string, string> strings { get; set; }

    string guid;

    static RazorViewEngineRender() {
        strings = new Dictionary<string, string>();
    }

    public RazorViewEngineRender(string Template) {
        guid = Guid.NewGuid().ToString() + ".cshtml";
        strings.Add(guid, Template);
    }

    public string Render() {
        return Render(null);
    }

    public string Render(object ViewModel) {
        //Register model type
        if (ViewModel == null) {
            strings[guid] = "@inherits System.Web.Mvc.WebViewPage\r\n" + strings[guid];
        } else {
            strings[guid] = "@inherits System.Web.Mvc.WebViewPage<" + ViewModel.GetType().FullName + ">\r\n" + strings[guid];
        }

        CshtmlView view = new CshtmlView("/stringviews/" + guid);

        System.Text.StringBuilder sb = new System.Text.StringBuilder();
        System.IO.TextWriter tw = new System.IO.StringWriter(sb);

        ControllerContext controller = new ControllerContext();

        ViewDataDictionary ViewData = new ViewDataDictionary();
        ViewData.Model = ViewModel;

        view.Render(new ViewContext(controller, view, ViewData, new TempDataDictionary(), tw), tw);
        //view.ExecutePageHierarchy();

        strings.Remove(guid);

        return sb.ToString();

    }
}

Global.asax

In your global.asax file you'll have to add the following to the Application_Start

System.Web.Hosting.HostingEnvironment.RegisterVirtualPathProvider(new Controllers.StringPathProvider());

Calling the code

string Template = "Hello, @Model.Name";
Models.User user = new Models.User() { Name = "Billy Boy" };
RazorViewEngineRender view = new RazorViewEngineRender(Template);
string Results = view.Render(user); //pass in your model

Notes

This only works with typed Models. I attempted to pass in a new { Name = "Billy Boy" } and it's throwing errors. I'm not sure why and didn't really look too deeply into it.

This was fun, thanks for asking this question.

Answer 2

Razor was designed with standalone operation in mind. There isn't much documentation about that mode yet (since it's all still under development) but have a look at this blog post by Andrew Nurse: http://vibrantcode.com/blog/2010/7/22/using-the-razor-parser-outside-of-aspnet.html