How to add Web API controller to an existing ASP.NET Core MVC?

Question

I created a project using the default ASP.NET Core MVC template. I would like to also create a RESTful API under /api/{Controller}. I added a new Web API controller (standard Web API controller class template) but I can't call it. I get an error saying that the page cannot be found. I tried adding a route in Startup.cs but it doesn't do anything:

app.UseMvc(routes => {     routes.MapRoute(name: "default", template: "{controller=Home}/{action=Index}/{id?}");     routes.MapRoute(name: "api", template: "api/{controller=Admin}"); }); 

EDIT:

Like I said, it's all default templates. Here's the Web API Controller that I added:

[Route("api/[controller]")] public class AdminController : Controller {                     // GET api/values/5     [HttpGet("{id}")]     public string Get(int id)     {         return "value";     }      // POST api/values     [HttpPost]     public void Post([FromBody]string value)     {     }      // PUT api/values/5     [HttpPut("{id}")]     public void Put(int id, [FromBody]string value)     {     }      // DELETE api/values/5     [HttpDelete("{id}")]     public void Delete(int id)     {     } } 

Answer 1

Two things.

First, when using convention-based routing, more specific routes should come before more generic routes to avoid route conflicts.

app.UseMvc(routes => {     routes.MapRoute(name: "api", template: "api/{controller=Admin}");     routes.MapRoute(name: "default", template: "{controller=Home}/{action=Index}/{id?}"); }); 

Secondly, you are already using attribute routing on the controller so should have been able to route to the controller except for the fact that you do not have a routing template on the controller that would accept /api/{Controller}

That would require a default route.

[Route("api/[controller]")] public class AdminController : Controller {       [HttpGet("")] //Matches GET api/admin <-- Would also work with [HttpGet]     public IActionResult Get() {         return Ok();     }      [HttpGet("{id}")] //Matches GET api/admin/5     public IActionResult Get(int id) {         return Ok("value");     }          //...other code removed for brevity } 

Answer 2

I had luck doing this with v3.1:

Add Folder Controllers to the project. Add Controller, named TestController, to the folder. Then add the following to the Startup.cs:

services.AddControllers(); 

to

public void ConfigureServices(IServiceCollection services)     {         services.AddRazorPages();         services.AddControllers();     } 

and:

endpoints.MapControllers(); 

to

app.UseEndpoints(endpoints =>         {             endpoints.MapRazorPages();             endpoints.MapControllers();         }); 

Then I was able to call /api/Test.