Using Razor outside of MVC in .NET Core

Question

I would like to use Razor as a templating engine in a .NET console application that I'm writing in .NET Core.

The standalone Razor engines I've come across (RazorEngine, RazorTemplates) all require full .NET. I'm looking for a solution that works with .NET Core.

Answer 1

Here is a sample code that only depends on Razor (for parsing and C# code generation) and Roslyn (for C# code compilation, but you could use the old CodeDom as well).

There is no MVC in that piece of code, so, no View, no .cshtml files, no Controller, just Razor source parsing and compiled runtime execution. There is still the notion of Model though.

You will only need to add following nuget packages: Microsoft.AspNetCore.Razor.Language (v2.1.1), Microsoft.AspNetCore.Razor.Runtime (v2.1.1) and Microsoft.CodeAnalysis.CSharp (v2.8.2) nugets.

This C# source code is compatible with NETCore, NETStandard 2 and .NET Framework. To test it just create a .NET framework or .NET core console app, paste it, and add the nugets.

using System;
using System.IO;
using System.Reflection;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Razor.Hosting;
using Microsoft.AspNetCore.Razor.Language;
using Microsoft.AspNetCore.Razor.Language.Extensions;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;

namespace RazorTemplate
{
    class Program
    {
        static void Main(string[] args)
        {
            // points to the local path
            var fs = RazorProjectFileSystem.Create(".");

            // customize the default engine a little bit
            var engine = RazorProjectEngine.Create(RazorConfiguration.Default, fs, (builder) =>
            {
                InheritsDirective.Register(builder);
                builder.SetNamespace("MyNamespace"); // define a namespace for the Template class
            });

            // get a razor-templated file. My "hello.txt" template file is defined like this:
            //
            // @inherits RazorTemplate.MyTemplate
            // Hello @Model.Name, welcome to Razor World!
            //

            var item = fs.GetItem("hello.txt");

            // parse and generate C# code, outputs it on the console
            //var cs = te.GenerateCode(item);
            //Console.WriteLine(cs.GeneratedCode);

            var codeDocument = engine.Process(item);
            var cs = codeDocument.GetCSharpDocument();

            // now, use roslyn, parse the C# code
            var tree = CSharpSyntaxTree.ParseText(cs.GeneratedCode);

            // define the dll
            const string dllName = "hello";
            var compilation = CSharpCompilation.Create(dllName, new[] { tree },
                new[]
                {
                    MetadataReference.CreateFromFile(typeof(object).Assembly.Location), // include corlib
                    MetadataReference.CreateFromFile(typeof(RazorCompiledItemAttribute).Assembly.Location), // include Microsoft.AspNetCore.Razor.Runtime
                    MetadataReference.CreateFromFile(Assembly.GetExecutingAssembly().Location), // this file (that contains the MyTemplate base class)

                    // for some reason on .NET core, I need to add this... this is not needed with .NET framework
                    MetadataReference.CreateFromFile(Path.Combine(Path.GetDirectoryName(typeof(object).Assembly.Location), "System.Runtime.dll")),

                    // as found out by @Isantipov, for some other reason on .NET Core for Mac and Linux, we need to add this... this is not needed with .NET framework
                    MetadataReference.CreateFromFile(Path.Combine(Path.GetDirectoryName(typeof(object).Assembly.Location), "netstandard.dll"))
                },
                new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary)); // we want a dll


            // compile the dll
            string path = Path.Combine(Path.GetFullPath("."), dllName + ".dll");
            var result = compilation.Emit(path);
            if (!result.Success)
            {
                Console.WriteLine(string.Join(Environment.NewLine, result.Diagnostics));
                return;
            }

            // load the built dll
            Console.WriteLine(path);
            var asm = Assembly.LoadFile(path);

            // the generated type is defined in our custom namespace, as we asked. "Template" is the type name that razor uses by default.
            var template = (MyTemplate)Activator.CreateInstance(asm.GetType("MyNamespace.Template"));

            // run the code.
            // should display "Hello Killroy, welcome to Razor World!"
            template.ExecuteAsync().Wait();
        }
    }

    // the model class. this is 100% specific to your context
    public class MyModel
    {
        // this will map to @Model.Name
        public string Name => "Killroy";
    }

    // the sample base template class. It's not mandatory but I think it's much easier.
    public abstract class MyTemplate
    {
        // this will map to @Model (property name)
        public MyModel Model => new MyModel();

        public void WriteLiteral(string literal)
        {
            // replace that by a text writer for example
            Console.Write(literal);
        }

        public void Write(object obj)
        {
            // replace that by a text writer for example
            Console.Write(obj);
        }

        public async virtual Task ExecuteAsync()
        {
            await Task.Yield(); // whatever, we just need something that compiles...
        }
    }
}

Answer 2

Recently I've created a library called RazorLight.

It has no redundant dependencies, like ASP.NET MVC parts and can be used in console applications. For now it only supports .NET Core (NetStandard1.6) - but that's exactly what you need.

Here is a short example:

IRazorLightEngine engine = EngineFactory.CreatePhysical("Path-to-your-views");

// Files and strong models
string resultFromFile = engine.Parse("Test.cshtml", new Model("SomeData")); 

// Strings and anonymous models
string stringResult = engine.ParseString("Hello @Model.Name", new { Name = "John" }); 

Answer 3

Here is a class to get Nate's answer working as a scoped service in an ASP.NET Core 2.0 project.

using System;
using System.IO;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Routing;

namespace YourNamespace.Services
{
    public class ViewRender : IViewRender
    {
        private readonly IRazorViewEngine _viewEngine;
        private readonly ITempDataProvider _tempDataProvider;
        private readonly IServiceProvider _serviceProvider;

        public ViewRender(
            IRazorViewEngine viewEngine,
            ITempDataProvider tempDataProvider,
            IServiceProvider serviceProvider)
        {
            _viewEngine = viewEngine;
            _tempDataProvider = tempDataProvider;
            _serviceProvider = serviceProvider;
        }

        public async Task<string> RenderAsync(string name)
        {
            return await RenderAsync<object>(name, null);
        }

        public async Task<string> RenderAsync<TModel>(string name, TModel model)
        {
            var actionContext = GetActionContext();

            var viewEngineResult = _viewEngine.FindView(actionContext, name, false);

            if (!viewEngineResult.Success)
            {
                throw new InvalidOperationException(string.Format("Couldn't find view '{0}'", name));
            }

            var view = viewEngineResult.View;

            using (var output = new StringWriter())
            {
                var viewContext = new ViewContext(
                    actionContext,
                    view,
                    new ViewDataDictionary<TModel>(
                        metadataProvider: new EmptyModelMetadataProvider(),
                        modelState: new ModelStateDictionary())
                    {
                        Model = model
                    },
                    new TempDataDictionary(
                        actionContext.HttpContext,
                        _tempDataProvider),
                    output,
                    new HtmlHelperOptions());

                await view.RenderAsync(viewContext);

                return output.ToString();
            }
        }

        private ActionContext GetActionContext()
        {
            var httpContext = new DefaultHttpContext {RequestServices = _serviceProvider};
            return new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
        }
    }

    public interface IViewRender
    {
        Task<string> RenderAsync(string name);

        Task<string> RenderAsync<TModel>(string name, TModel model);
    }
}

In Startup.cs

public void ConfigureServices(IServiceCollection services)
{
     services.AddScoped<IViewRender, ViewRender>();
}

In a controller

public class VenuesController : Controller
{
    private readonly IViewRender _viewRender;

    public VenuesController(IViewRender viewRender)
    {
        _viewRender = viewRender;
    }

    public async Task<IActionResult> Edit()
    {
        string html = await _viewRender.RenderAsync("Emails/VenuePublished", venue.Name);
        return Ok();
    }
}

Answer 4

There's a working example for .NET Core 1.0 at aspnet/Entropy/samples/Mvc.RenderViewToString. Since this might change or go away, I'll detail the approach I'm using in my own applications here.

Tl;dr - Razor works really well outside of MVC! This approach can handle more complex rendering scenarios like partial views and injecting objects into views as well, although I'll just demonstrate a simple example below.

---

The core service looks like this:

RazorViewToStringRenderer.cs

using System;
using System.IO;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Routing;

namespace RenderRazorToString
{
    public class RazorViewToStringRenderer
    {
        private readonly IRazorViewEngine _viewEngine;
        private readonly ITempDataProvider _tempDataProvider;
        private readonly IServiceProvider _serviceProvider;

        public RazorViewToStringRenderer(
            IRazorViewEngine viewEngine,
            ITempDataProvider tempDataProvider,
            IServiceProvider serviceProvider)
        {
            _viewEngine = viewEngine;
            _tempDataProvider = tempDataProvider;
            _serviceProvider = serviceProvider;
        }

        public async Task<string> RenderViewToString<TModel>(string name, TModel model)
        {
            var actionContext = GetActionContext();

            var viewEngineResult = _viewEngine.FindView(actionContext, name, false);

            if (!viewEngineResult.Success)
            {
                throw new InvalidOperationException(string.Format("Couldn't find view '{0}'", name));
            }

            var view = viewEngineResult.View;

            using (var output = new StringWriter())
            {
                var viewContext = new ViewContext(
                    actionContext,
                    view,
                    new ViewDataDictionary<TModel>(
                        metadataProvider: new EmptyModelMetadataProvider(),
                        modelState: new ModelStateDictionary())
                    {
                        Model = model
                    },
                    new TempDataDictionary(
                        actionContext.HttpContext,
                        _tempDataProvider),
                    output,
                    new HtmlHelperOptions());

                await view.RenderAsync(viewContext);

                return output.ToString();
            }
        }

        private ActionContext GetActionContext()
        {
            var httpContext = new DefaultHttpContext
            {
                RequestServices = _serviceProvider
            };

            return new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
        }
    }
}

A simple test console app just needs to initialize the service (and some supporting services), and call it:

Program.cs

using System;
using System.Diagnostics;
using System.IO;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Hosting.Internal;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.FileProviders;
using Microsoft.Extensions.ObjectPool;
using Microsoft.Extensions.PlatformAbstractions;

namespace RenderRazorToString
{
    public class Program
    {
        public static void Main()
        {
            // Initialize the necessary services
            var services = new ServiceCollection();
            ConfigureDefaultServices(services);
            var provider = services.BuildServiceProvider();

            var renderer = provider.GetRequiredService<RazorViewToStringRenderer>();

            // Build a model and render a view
            var model = new EmailViewModel
            {
                UserName = "User",
                SenderName = "Sender"
            };
            var emailContent = renderer.RenderViewToString("EmailTemplate", model).GetAwaiter().GetResult();

            Console.WriteLine(emailContent);
            Console.ReadLine();
        }

        private static void ConfigureDefaultServices(IServiceCollection services)
        {
            var applicationEnvironment = PlatformServices.Default.Application;
            services.AddSingleton(applicationEnvironment);

            var appDirectory = Directory.GetCurrentDirectory();

            var environment = new HostingEnvironment
            {
                WebRootFileProvider = new PhysicalFileProvider(appDirectory),
                ApplicationName = "RenderRazorToString"
            };
            services.AddSingleton<IHostingEnvironment>(environment);

            services.Configure<RazorViewEngineOptions>(options =>
            {
                options.FileProviders.Clear();
                options.FileProviders.Add(new PhysicalFileProvider(appDirectory));
            });

            services.AddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();

            var diagnosticSource = new DiagnosticListener("Microsoft.AspNetCore");
            services.AddSingleton<DiagnosticSource>(diagnosticSource);

            services.AddLogging();
            services.AddMvc();
            services.AddSingleton<RazorViewToStringRenderer>();
        }
    }
}

This assumes that you have a view model class:

EmailViewModel.cs

namespace RenderRazorToString
{
    public class EmailViewModel
    {
        public string UserName { get; set; }

        public string SenderName { get; set; }
    }
}

And layout and view files:

Views/_Layout.cshtml

<!DOCTYPE html>

<html>
<body>
    <div>
        @RenderBody()
    </div>
    <footer>
Thanks,<br />
@Model.SenderName
    </footer>
</body>
</html>

Views/EmailTemplate.cshtml

@model RenderRazorToString.EmailViewModel
@{ 
    Layout = "_EmailLayout";
}

Hello @Model.UserName,

<p>
    This is a generic email about something.<br />
    <br />
</p>