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Mvc routing. How can i set a default parameter in .net core 3.0?

My controller is
public partial class GridController : Controller
{
[Route("/grid/{name}")]
public IActionResult Index(string name)
{
}
}
Routing is setup correctly since if i visit /grid/something i get http ok.
But how can i set a default parameter in startup.cs?
I tried the following but on page load, i get http 404 error
endpoints.MapControllerRoute(
"default",
"{controller=Grid}/{action=Index}/{name}");

Okay. Ended up with a workaround
endpoints.MapControllerRoute(
"default",
"{controller=Grid}/{action=Index}");
and by adding an extra action overload.
public IActionResult Index()
{
return Index("something");
}
it simply works
[Route("/grid/{name}")]
public IActionResult Index(string name )
{
}

Use attribute routing at Controller level, So that it will be applicable to all the action method under that controller.

In your route template. The name parameter is not optional.
So, use {name?}.

First of all, you did not specify the name parameter in your endpoint configuration. So it should have been {controller=Grid}/{action=Index}/{name=something}. But if there are overloads, this does not seem to work anyway. I wonder if this is a bug or is it intended by design. It seems that if there is are multiple overloads of the same action, execution gets directed to the parameterless one.
Here's another workaround with the possibility to use parameters. I tried this with .NET Core 2.2. Create a new action with the same parameters, but without RouteAttribute. From there you can do a redirect to the necessary action. Here's an example where I use TestIndex for the default route.
[Route("/[controller]/{name}/{age}")]
public IActionResult Index(string name, int age)
{
// implementation
return Ok($"{name} is {age} years old.");
}
public IActionResult Index()
{
return Index("Mr. It", 7);
}
public IActionResult TestIndex(string name, int age)
{
return RedirectToAction(nameof(Index), new { name, age });
}
Then for default route use the new method, e.g. {controller=Grid}/{action=TestIndex}/{name=That}/{age=42}.
If you use this for testing, the new action could be omitted from production by adding a TypeFilterAttribute. See this answer for more details.

Cannot generate correct links

I have the following code in a razor page:
#Url.Action("ArticleDetails", "Information", new { slug = article.Slug })
The page url where this code is placed has the form of http://localhost/category/6/category-name where 6 is the ID of the category
In the InformationController I have the following actions:
[HttpGet("article/{id}/{slug}")]
public IActionResult ArticleDetails(int id, string slug)
{
// some code ...
return View(data);
}
[HttpGet("article/{slug}")]
public IActionResult ArticleDetails(string slug)
{
// some code ...
return View(data);
}
How can I reach URL of form article/article-slug because #Url.Action(...) that I have in the page always try to reach controller action with id even if ID is not supplied as an anonymous type.
Links take the form of article/6/article-slug instead I want them to be article/article-slug without removing action with id in the controller.
I have noticed that 6 is from the id of the category. Also if I delete the controller action with Id i get the correct format of URL.

When resolving the action you're linking to, the IUrlHelper instance is using the current value of id in your current route (http://localhost/category/6/category-name), which has a value of 6, as you stated in your OP. Because there exists an ArticleDetails action that takes both an id and a slug (which you provide explicitly), the ArticleDetails action that takes both of these parameters is selected.
In order to resolve this, there are a couple of options. The first option is to clear out the RouteData value once you've used it in the action invoked when reaching http://localhost/category/6/category-name. In order to do that, you can use the following code within said action:
RouteData.Values.Remove("id");
I'm not a fan of doing it this way, but it does work. IMO, a better approach would be to simply use different names for the id parameter: e.g. categoryId and articleId in the respective controllers. This both fixes your issue and makes the code more readable in the corresponding actions. Your ArticleDetails action would simply change to:
[HttpGet("article/{articleId}/{slug}")]
public IActionResult ArticleDetails(int articleId, string slug)
{
// some code ...
return View(data);
}

Routing can be finicky when trying to do overloads like this. Your best bet is to use named routes:
[HttpGet("article/{id}/{slug}", Name = "ArticleDetailsIdSlug")]
public IActionResult ArticleDetails(int id, string slug)
[HttpGet("article/{slug}", Name = "ArticleDetailsSlug")]
public IActionResult ArticleDetails(string slug)
Then, in your view:
#Url.RouteUrl("ArticleDetailsSlug", new { slug = article.Slug })
Now, the routing framework doesn't have to try to figure out which route you actually want (and guess incorrectly apparently), as you'd told it exactly which route to use.

How to create a route attribute which handles missing middle parameters?

If I have the code below and when the firstname is missing in the url, I get a 404 error. See first example below. I am not sure why the route doesn't work in this case when the attribute names are in the url are there are placeholders for the values. My solution is to create another route and use another url format but that's more work. What if I have many parameters and some in the middle are missing their values, isn't there a single route that can handle all of the instances?
How do I create a single route which can handle the four combinations in the below example? Both are missing. Both are present. One of them is missing.
[HttpGet]
[Route("getcustomer/firstname/{firstname?}/status/{status?}")]
public IHttpActionResult GetCustomer(string firstname = null, string status = null)
{
... some code ...
}
**Example URLs:**
http://.../getcustomer/firstname//status/valid" causes 404
http://.../getcustomer/firstname/john/status/active" good
http://.../getcustomer/firstname/john/status/" good

That is by design. You may need to create another action to allow for that. Also in terms of how the framework is built. the end segments are the ones that should be optional.
You need to rethink your design.
For example
[RoutePrefix("api/customers")]
public class CustomersController : ApiController {
[HttpGet]
[Route("")] // Matches GET api/customers
public IHttpActionResult GetCustomer(string firstname = null, string status = null) {
... some code ...
}
}
Example URLs:
http://...api/customers
http://...api/customers?status=valid
http://...api/customers?firstname=john&status=active
http://...api/customers?firstname=john

No HTTP resource was found that matches the request URI - and - No action was found on the controller that matches the request

I am trying to build out a new endpoint in API app that already has a lot of other endpoints working just fine. Not sure what I'm doing wrong. I am getting two errors:
Message: No HTTP resource was found that matches the request URI 'http://localhost:62342/api/VoiceMailStatus
and
MessageDetail: No action was found on the controller 'VoiceMailStatus' that matches the request.
Here's the controller:
public class VoiceMailStatusController : ControllerBase
{
[HttpPost]
[Route("api/VoiceMailStatus")]
public string VoiceMailStatus(string var)
{
...
}
}
And here's the route:
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
I'm using PostMan:
There are a LOT of threads here about both of these error messages. I've read many of them, but have yet to find a solution. One of them said to change this:
public string VoiceMailStatus(string var)
to this:
public string VoiceMailStatus(string var = "")
And while that did get the error to go away and I was able to get inside of the method while in debug, var was always just an empty string.
EDIT: GOT IT WORKING
In addition to adding [FromBody] as per Andrii Litvinov's answer, I also had to do one more thing. What had been this:
public string VoiceMailStatus(string var)
{
...
}
Is now this:
public string VoiceMailStatus([FromBody] VMStatus request)
{
...
}
And then VMStatus is just a small little class with a single string property:
public class VMStatus
{
public string var { get; set; }
}

Most likely you need to apply FromBody attribute to your parameter:
public string VoiceMailStatus([FromBody] string var)
If that does not help try to rename parameter to something else, e.g.: var1, because var is reserved work in C# and could cause some binding issues, but I doubt that's the case.

You probably want to add this to your controller since you have api in the route config:
[RoutePrefix("API/VoiceMailStatus")]
and then add this to your action:
[Route("VoiceMailStatus", Name = "VoiceMailStatus")]
This should tie the action to the url localhost/api/voicemailstatus/voicemailstatus

call to web api with string parameter

I have a web api where I have 2 methods, one without parameter and two with different types of parameter (string and int). When calling the string method it doesnt work...what am I missing here?
public class MyControllerController : ApiController
{
public IHttpActionResult GetInt(int id)
{
return Ok(1);
}
public IHttpActionResult GetString(string test)
{
return Ok("it worked");
}
}
WebApiConfig.cs:
public static void Register(HttpConfiguration config)
{
// Web API configuration and services
// Web API routes
config.MapHttpAttributeRoutes();
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
}
My Call:
/api/MyController/MyString //Doesnt work
/api/MyController/1 //work
I get following error:
The parameters dictionary contains a null entry for parameter 'id' of non-nullable type 'System.Int32' for method 'System.Web.Http.IHttpActionResult GetInt(Int32)' in 'TestAngular.Controllers.MyControllerController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter.
What am I missing in my request?

Here is my solution:
without changing default route in webapiconfig.cs file
add just a route to your string function:
[Route("Api/MyController/GetString/{test}")]
public IHttpActionResult GetString(string test)
http://localhost:49609/api/MyController/GetString/stringtest

Also this uri's should work:
api/MyController/GetAll
api/MyController/GetString?param=string
api/MyController/GetInt?param=1
I think this is much clearer and should always work.
You use the routing behavior.
See here:
http://www.asp.net/web-api/overview/web-api-routing-and-actions/routing-and-action-selection

You have to change your uri's
/api/MyController
/api/MyController/string
/api/MyController/1
You don't have to specify the methods.
You could take look at this tutorial on asp.net for further clarification.

It's been a while since you posted this, but I think I have the answer.
First off, there are two issues. First, as Pinback noted, you can't use the same route for two different endpoints.
However if you just eliminate the int method, you'll still run into the problem.
Remember: the default route looks like this: api/{controller}/{id}
In order to bind the parameter, it has to be called "id", and not "test".
Change the signature to this:
public IHttpActionResult GetString(string id)
and it will work.
(you can also change {id} to {test} in the webapiconfig.cs file).

You can also take string parameter in body
string body;
using (var sr = new StreamReader(Request.Body))
body = sr.ReadToEnd();