A project for supporting API Endpoints in ASP.NET Core web applications.

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MVC Controllers are essentially an antipattern. They're dinosaurs. They are collections of methods that never call one another and rarely operate on the same state. They're not cohesive. They tend to become bloated and to grow out of control. Their private methods, if any, are usually only called by a single public method. Most developers recognize that controllers should be as small as possible (unscientific poll), but they're the only solution offered out of the box, so that's the tool 99% of ASP.NET Core developers use.

You can use tools like MediatR to mitigate the problem. You can read a detailed article about how to migrate from Controllers to Endpoints using MediatR. The short version is that MediatR enables you to have single-line action methods that route commands to handlers. This is objectively a better approach, resulting in more cohesive classes that better follow OO principles. But what if you didn't even need that extra plumbing?

That's what ASP.NET Core API Endpoints are all about.

The .NET team already did this exact thing with razor pages. They recognized that dealing with Views, ViewModels, Controllers, and Actions was way more complicated than necessary. It required a developer to jump around between at least 3 (and often more) different folders in order to add or modify a new page/view to their project. Razor pages addressed this by rethinking the model for page-based ASP.NET Core MVC endpoints.

Razor Pages group each page's razor markup, its related action(s), and its model into two linked files. It uses the same MVC features as the rest of the platform, so you still get routing, model binding, model validation, filters, the works. You literally give up nothing. But now when you need to add or modify a page you need to look at exactly 2 files, which are linked in the IDE so you don't need to scroll around the file system looking for them.

ASP.NET Core API Endpoints are essentially Razor Pages for APIs. They break apart bloated controllers and group the API models used by individual endpoints with the endpoint logic itself. They provide a simple way to have a single file for the logic and linked files for the model types.

When working with ASP.NET Core API Endpoints your project won't need any Controller classes. You can organize the Endpoints however you want. By feature. In a giant Endpoints folder. It doesn't matter - they'll work regardless of where you put them.

Most REST APIs have groups of endpoints for a given resource. In Controller-based projects you would have a controller per resource. When using API Endpoints you can simply create a folder per resource, just as you would use folders to group related pages in Razor Pages.

I'll look to add detailed documentation in the future but for now here's all you need to get started (you can also check the sample project):

1. Add the Ardalis.ApiEndpoints NuGet package to your ASP.NET Core web project.
2. Create Endpoint classes by inheriting from either BaseEndpoint<TRequest,TResponse> (for endpoints that accept a model as input) or BaseEndpoint<TResponse> (for endpoints that simply return a response). For example, a POST endpoint that creates a resource and then returns the newly created record would use version that includes both a Request and a Response. A GET endpoint that just returns a list of records and doesn't accept any arguments would use the second version.
3. Implement the base class's abstract Handle() method.
4. Make sure to add a [HttpGet] or similar attribute to your Handle() method, specifying its route.
5. Define your TResponse type in a file in the same folder as its corresponding endpoint.
6. Define your TRequest type (if any) just like the TResponse class.
7. Test your ASP.NET Core API Endpoint. If you're using Swagger/OpenAPI it should just work with it automatically.

Below are what I expect will be some common questions:

If you want to create a common route template for all or some subset of your Endpoints, simply create a BaseEndpoint of your own that inherits from Ardalis.Api.Endpoints.BaseEndpoint and add a [Route] attribute to it.

Technically, yes. But don't do that. If you really want that, you should just use a Controller.

The following are some things I'd like to add to the project/package.

An analyzer could detect if more than one public method were added to a Handler, for instance.

Visual Studio and/or CLI item templates would make it much easier to create Endpoints and their associated models, with the correct naming so they're linked in the IDE.

One thing that Controllers do have is built-in support in the framework to use their name in routes (e.g. "/[controller]/{id?}"). Currently in the sample app routes are hard-coded strings. It would be nice if there were an easy way to use a convention based on foldername or namespace or something (using foldername would align with how Razor Pages routing works).