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Dynamic Data Binding Of Email Body Template Using .NET Core Razor Library

In general, there are two most common approaches to build an email template like:
  • System.Text.StringBuilder using this we generate template by appending n-number of strings. This approach is hard to maintain, can not do code debug, etc.
  • Another approach is like storing the entire email template in the database, where the template contains a placeholder to be replaced with dynamic data. Compare to the StringBuilder approach, the preferring database will make code Maintainance easy. But in this approach also debug code is hard.

What Kind Of Solution Razor Library Provides?:

Razor Library is a .Net Standard Library that has an inbuild razor engine where we can create Razor Page, MVC Views. It works as similar to MVC Views or Razor Pages where generate pages with Model binding.

So by using the Razor Library, we need to create a custom provider Razor Engine where we can fetch the Html of the page render using Model binding. So in this approach, we create Mvc View or Razor Page (.cshtml), to these pages we need to pass our required model for data binding. After successfully binding dynamic data we need to fetch *.cshtml content as a string to send as email body template.

This approach benefits us like easy code maintenance, good to debug the code like the normal MVC View, or Razor Page.

Create A .Net Core MVC Application:

Let's create a sample MVC application to get hands-on experience on this Dynamic Email Body Template creation.

OverView On Email Body With StringBuilder:

Note:
Skip this StringBuilder overview section if you have prior knowledge on email body template creation. The purpose of the section to give basic understanding on one of the old technique to those who doesn't have any knowledge on email body generation.
Let's create a sample email body using StringBuilder. Now add a new action method in HomeController.cs as below
Controllers/HomeController.cs:
[HttpGet]
[Route("email-body")]
public IActionResult EmailBody()
{
	string imageUrl = "https://localhost:5001/img/profile.webp";
	string firstName = "Naveen";
	string secondName = "bommidi";
	StringBuilder sb = new StringBuilder();
	sb.AppendFormat("<div class='row'>");
	sb.AppendFormat("<div class='col-sm-4'>");
	sb.AppendFormat("<div class='card'>");
	sb.AppendFormat("<img src='{0}' class='card-img-top'>", imageUrl);
	sb.AppendFormat("<div class='card-body'>");
	sb.AppendFormat("<h4 Card-title>{0} {1}</h4>", new object[] { firstName, secondName });
	sb.AppendFormat("</div>");
	sb.AppendFormat("</div>");
	sb.AppendFormat("</div>");
	sb.AppendFormat("</div>");

	string emailBody = sb.ToString();

	// write your logic to sending email

	return View("emailPreview",emailBody);
}
  • #L5,6,7 these lines show the data that need to bind to the email body template.
  • #L8 initialized StringBuilder object.
  • #L20 Convert entire StringBuilder object to normal string
  • #L22 comment shows where we need to implement email sending logic which not part of our topic.
  • #L24 we sending email body to *.cshtml file for preview the email output(it is development time code never do it in production)
  • From this sample code, we can understand this approach is hard to maintain, and updating any changes to the template will be not so easy.
To test or preview the email body(at the time of development) add the following code to emailPreview.cshtml page.
Views/Home/emailPreview.cshtml:
@model string

@Html.Raw(Model)

Add Razor Library:

Now let's explore the Razor library technique to create an email body in a more efficient way.

Let's select to add a Razor Class Library template.
After adding the Razor Class Library project structure looks as follows.

Add Email Body Html To View With Model Binding:

In the Razor Class Library template, we need to create views for email HTML body with dynamic binding. So let's store all our email view template inside the Areas(default framework folder).
Let's first create a model class for model binding in our email body template view files. Let's add the following sample model in Razor Class Library.
Models/Profile.cs:(Razor Class Library Project template)
namespace RazorLib.Models
{
    public class Profile
    {
        public string AvatarLink { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }
}
Now add View with model binding in Razor Class Library.
Areas/MyFeature/Views/Profile/ProfileEmailBody.cshtml:(Razor Class Library)
@model RazorLib.Models.Profile

<div class="row">
    <div class="col-sm-4">
        <div class="card">
            <img src="@Model.AvatarLink" class="card-img-top">
            <div class="card-body">
                <h4 Card-title>@Model.FirstName @Model.LastName</h4>
            </div>
        </div>
    </div>
</div>
Now we have created Html Body inside View page, next, we need to implement a custom Razor Engine to read the razor views.

Custom Razor View Engine:

Now to execute the Views with Model binding and then to fetch Html output, we need to implement a custom Razor View Engine. This custom Razor View Engine exactly works like default view engine works in MVC or Razor Page .Net Core Framework template application. This is like creating a Razor View Engine explicitly in our Razor Class Library.

Let's implement a Custom Razor View Engine by injecting necessary services into it like below.
Services/CustomRazorEngine.cs:(Razor Class Library):
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using System;

namespace RazorLib.Services
{
    public class CustomRazorEngine
    {
        private readonly IRazorViewEngine _razorViewEngine;
        private readonly ITempDataProvider _tempDataProvider;
        private readonly IServiceProvider _serviceProvider;
        public CustomRazorEngine(
            IRazorViewEngine razorViewEngine,
            ITempDataProvider tempDataProvider,
            IServiceProvider serviceProvider
            )
        {
            _razorViewEngine = razorViewEngine;
            _tempDataProvider = tempDataProvider;
            _serviceProvider = serviceProvider;
        }
    }
}
  • Microsoft.AspNetCore.Mvc.Razor.IRazorViewEngine - used to render the pages that use razor syntax.
  • Microsoft.AspNetCore.Mvc.ViewFeatures.ITempDataProvider - temporary storage memory for subsequent request.
  • System.IServiceProvider - provider for creating instances.
Razor View Engine must identify the required view page that needs to be rendered. So let's implement a new private method in our CustomRazorEngine class as below.
Services/CustomRazorEngine.cs:
private IView FindView(string ViewName)
{
	ViewEngineResult viewResult = _razorViewEngine.GetView(executingFilePath: null, viewPath: ViewName, isMainPage: true);
	if (viewResult.Success)
	{
		return viewResult.View;
	}
	throw new Exception("Invalid View Path");
}
  • #L1 this line show private method returns an IView type and this method expecting input parameter of the View name. Absolute file path included along with view name as an input parameter. If you want you can specify different parameters like one for view name and another for view absolute path.
  • #L3 Microsoft.AspNetCore.Mvc.Razor.IRazorViewEngine.GetView() - this method expecting 3 parameters. the first parameter like an absolute path to the view and it set null value in our implementation since we pass full absolute path along with view name. The second parameter expects either only view name or absolute path along with view name.
  • #L4, L6 If our engine able to find the expected view page it will be returning as output.
  • #L8 If our razor engine unable to find view then throw a custom exception like above code snippet.
Now implement a private method that creates basic Microsoft.AspNetCore.Mvc.ActionContext instance as below.
Services/CustomRazorEngine.cs:
private ActionContext GetContext()
{
	var httpContext = new DefaultHttpContext();
	httpContext.RequestServices = _serviceProvider;
	return new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
}
In a normal web request for MVC or Razor Page Microsoft.AspNetCore.Mvc.ActionContext will be created by the framework. Since we are using Custom Razor View Engine we need to create a basic instance of Microsoft.AspNetCore.Mvc.ActionContext which some default values like HttpContex, RouteData and ActionDescriptor.

Let's start implementing how our custom Razor View Engine outputs the Html as below.
Services/CustomRazorEngine.cs:
public async Task<string> RazorViewToHtmlAsync<TModel>(string viewName, TModel model)
{
	var actionContext = GetContext();
	var view = FindView(viewName);

	using(var output = new StringWriter())
	{
		var viewContext = new ViewContext(
			actionContext: actionContext,
			view: view,
			viewData: new ViewDataDictionary<TModel>(
				metadataProvider: new EmptyModelMetadataProvider(),
				modelState: new ModelStateDictionary()
				)
			{
				Model = model
			},
			tempData: new TempDataDictionary(actionContext.HttpContext, _tempDataProvider),
			writer: output,
			htmlHelperOptions: new HtmlHelperOptions()
			);
		await view.RenderAsync(viewContext);
		return output.ToString();
	}
}
  • #L6 using System.Io.StringWriter stream to capture the rendered view HTML content
  • #L8 Microsoft.AspNetCore.Mvc.Rendering.ViewContext instance is the triggering point where it renders a View or Razor Page with model binding and writes the generated Html as a stream to System.Io.StringWriter.
  • #L10 view to be rendered.
  • #L16 view model.
  • #L19 Html content stream wirter.
Finally, custom Razor View Engine implementation looks as below.
Services/ICustomRazorEngine:
using System.Threading.Tasks;

namespace RazorLib.Services
{
    public interface ICustomRazorEngine
    {
        Task<string> RazorViewToHtmlAsync<TModel>(string viewName, TModel model);
    }
}
Services/CustomRazorEngine:
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.ViewEngines;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Routing;
using System;
using System.IO;
using System.Threading.Tasks;

namespace RazorLib.Services
{
    public class CustomRazorEngine: ICustomRazorEngine
    {
        private readonly IRazorViewEngine _razorViewEngine;
        private readonly ITempDataProvider _tempDataProvider;
        private readonly IServiceProvider _serviceProvider;
        public CustomRazorEngine(
            IRazorViewEngine razorViewEngine,
            ITempDataProvider tempDataProvider,
            IServiceProvider serviceProvider
            )
        {
            _razorViewEngine = razorViewEngine;
            _tempDataProvider = tempDataProvider;
            _serviceProvider = serviceProvider;
        }

        private IView FindView(string ViewName)
        {
            ViewEngineResult viewResult = _razorViewEngine.GetView(executingFilePath: null, viewPath: ViewName, isMainPage: true);
            if (viewResult.Success)
            {
                return viewResult.View;
            }
            throw new Exception("Invalid View Path");
        }

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

        public async Task<string> RazorViewToHtmlAsync<TModel>(string viewName, TModel model)
        {
            var actionContext = GetContext();
            var view = FindView(viewName);

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

Integrate Razor Class Library Into MVC Application:

Razor Class Library reference into MVC application as below.

Now register our custom razor view engine provider in the ConfigureServices method in Startup.cs file in our MVC application as below.
Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
  //existing code hidden for display purpose 
  services.AddScoped<ICustomRazorEngine, CustomRazorEngine>();
}
Now inject custom razor view engine provider into HomeController.cs as follow.
Controllers/HomeController.cs:
using RazorLib.Services;

namespace EmailTemplate.MVC.Controllers
{
    public class HomeController : Controller
    {
        private readonly ICustomRazorEngine _customRazorEngine;

        public HomeController(ICustomRazorEngine customRazorEngine)
        {
            _customRazorEngine = customRazorEngine;
        }
    }
}

Update MVC Action Method To Generate Email Body:

Implement an action method to consume the custom razor engine provider. Need to specify the view page path and view model for data binding to custom razor engine provider.
Controllers/HomeController.cs:
[HttpGet]
[Route("email-body")]
public async Task<IActionResult> EmailBody()
{
	var profile = new Profile
	{
		AvatarLink = "https://localhost:5001/img/profile.webp",
		FirstName = "Naveen",
		LastName = "Bommidi"
	};

	string emailBody = await _customRazorEngine
		.RazorViewToHtmlAsync<Profile>("Areas/MyFeature/Views/Profile/ProfileEmailBody.cshtml", profile);

	// write your logic to sending email

	return View("emailPreview",emailBody);
}
  • #L5 view model created
  • #L12,13 view path and view model are passing as input parameters to the custom razor view engine provider.
  • #L15 comment represents need to configure email sending logic
  • #L17 is an optional line of code used to preview the email body at the time of development.
Html output preview:-

That's all about dynamic data binding of email body template using .NET Core razor library in an efficient approach.

Wrapping Up:

Hopefully, I think this article delivered some useful information about the Email Body Template Generation Using .Net Core Razor Library. I love to have your feedback, suggestions, and better techniques in the comment section below.

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