Bare metal APIs with ASP.NET Core MVC

ASP.NET Core MVC now provides a true “one asp.net” framework that can be used for building both APIs and websites. But what if you only want to build an API?

Most of the ASP.NET Core MVC tutorials I’ve seen advise using the Microsoft.AspNetCore.Mvc package. While this does indeed give you what you need to build APIs, it also gives you a lot more:

• Microsoft.AspNetCore.Mvc.ApiExplorer
• Microsoft.AspNetCore.Mvc.Cors
• Microsoft.AspNetCore.Mvc.DataAnnotations
• Microsoft.AspNetCore.Mvc.Formatters.Json
• Microsoft.AspNetCore.Mvc.Localization
• Microsoft.AspNetCore.Mvc.Razor
• Microsoft.AspNetCore.Mvc.TagHelpers
• Microsoft.AspNetCore.Mvc.ViewFeatures
• Microsoft.Extensions.Caching.Memory
• Microsoft.Extensions.DependencyInjection
• NETStandard.Library

A few of these packages are still needed if you’re building APIs but many are specific to building full websites.

After installing the above package we typically register MVC in Startup.ConfigureServices like so:

services.AddMvc();

This code is responsible for wiring up the necessary MVC services with application container. Let’s look at what this actually does:

public static IMvcBuilder AddMvc(this IServiceCollection services)
{
    var builder = services.AddMvcCore();

    builder.AddApiExplorer();
    builder.AddAuthorization();

    AddDefaultFrameworkParts(builder.PartManager);

    // Order added affects options setup order

    // Default framework order
    builder.AddFormatterMappings();
    builder.AddViews();
    builder.AddRazorViewEngine();
    builder.AddCacheTagHelper();

    // +1 order
    builder.AddDataAnnotations(); // +1 order

    // +10 order
    builder.AddJsonFormatters();

    builder.AddCors();

    return new MvcBuilder(builder.Services, builder.PartManager);
}

Again most of the service registration refers to the components used for rendering web pages.

Bare Metal APIs

It turns out that the ASP.NET team anticipated that developers may only want to build APIs and nothing else, so they gave us the ability to do just that.

First of all, rather than installing Microsoft.AspNetCore.Mvc, only install Microsoft.AspNetCore.Mvc.Core. This will give you the bare MVC middleware (routing, controllers, HTTP results) and not a lot else.

In order to process JSON requests and return JSON responses we also need the Microsoft.AspNetCore.Mvc.Formatters.Json package.

Then, to add both the core MVC middleware and JSON formatter, add the following code to ConfigureServices:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvcCore()
        .AddJsonFormatters();
}

The final thing to do is to change your controllers to derive from ControllerBase instead of Controller. This provides a base class for MVC controllers without any View support.

Looking at the final list of packages in project.json, you can see we really don’t need that much after all, especially given most of these are related to configuration and logging:

"Microsoft.AspNetCore.Mvc.Core": "1.1.0",
"Microsoft.AspNetCore.Mvc.Formatters.Json": "1.1.0",
"Microsoft.AspNetCore.Server.IISIntegration": "1.1.0",
"Microsoft.AspNetCore.Server.Kestrel": "1.1.0",
"Microsoft.Extensions.Configuration.EnvironmentVariables": "1.1.0",
"Microsoft.Extensions.Configuration.FileExtensions": "1.1.0",
"Microsoft.Extensions.Configuration.Json": "1.1.0",
"Microsoft.Extensions.Configuration.CommandLine": "1.1.0",
"Microsoft.Extensions.Logging": "1.1.0",
"Microsoft.Extensions.Logging.Console": "1.1.0",
"Microsoft.Extensions.Logging.Debug": "1.1.0"

You can find the complete code on GitHub.