Using Razor outside of MVC for building custom middleware or other generation stuff

16 January 2017 Peter-Himschoot

Recently I have been building some asp.net core middleware which involves generating some html from a collection of elements.

Writing code to generate html is no fun at all, so I decided to see if I could not use Razor outside of the normal MVC stack.

Simple answer: yes! 

I've published this as a package on NuGet.org (scroll down for sources):

U2U.AspNetCore.Mvc.Razor

Use razor to generate files outside of the normal MVC Controller/View chain, for example in your middleware, or for sending dynamic email messages.

All you need is a HttpContext.

To generate contents from Razor as a string

Start by creating a viewModel instance. The ViewModel is used to pass data to the Razor file, ViewData or ViewBag is not supported.

Create a Razor file, using the ViewModel's class as the @model:

@model TestRazor.Models.RazorViewModel

Your message: @Model.Message

Then call the RenderToStringAsync method (which is an extension method on HttpContext) passing the path to the razor file and the viewmodel. You will get the result back as a string.

var viewModel = new RazorViewModel { Message = "Generated from razor!" };
var contents = await HttpContext.RenderToStringAsync("~/Views/Home/Razor.cshtml", viewModel);

To generate Razor contents to the response stream

Start by creating a viewModel instance. The ViewModel is used to pass data to the Razor file, ViewData or ViewBag is not supported.

Create a Razor file, using the ViewModel's class as the @model:

@model IEnumerable<U2U.AspNetCore.NotFound.NotFoundRequest>

<!DOCTYPE html>
<html>
<body>
  <h1>Fix 404s</h1>
  <table>
    <thead id="requestHeader">
      <tr>
        <th class="path">Path</th>
        <th>404 Count</th>
        <th>Corrected Path</th>
      </tr>
    </thead>
    <tbody>
      @foreach (var request in Model)
      {
        <tr class="requestRow">
          <td>@request.Path</td>
          <td>@request.Hits</td>"
          @if (!String.IsNullOrEmpty(request.FixedPath))
          {
          <td>@request.FixedPath</td>
          }
          else
          {
          <td>
            <input type="text" />
            <a href='@string.Format("?path={0}&fixedPath=", request.Path)' class="fixLink">Save</a>
          </td>
          }
        </tr>
        }
      </tbody>
    </table>
  </body>
</html>

Then call the RenderToStringAsync method (which is an extension method on HttpContext) passing the path to the razor file and the viewmodel. The resulting razor content is written to the result stream.

var viewModel = tracker.NotFoundRequests.OrderByDescending(r => r.Hits).ToList();
await context.RenderAsync("~/Views/Shared/NotFound.cshtml", viewModel);

Sources

Sources of this package are available on github repository https://github.com/PeterHimschoot/U2U.AspNetCore.Mvc.Razor

Any bugs, remarks, etc... can always be sent to peter@u2u.be

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