When I use HttpGet(...), intellisense tells me that besides the first argument, i.e. pattern, I also have name and order. While the latter is obvious to me, I got a bit uncertain on what the parameter name had as its purpose.
Heading over to the docs, I see that the constructor of HttpGet only declares a single parameter. That confused me and I suspect that I'm missing something or using the Framework's version instead of Core, or something.
As I can see the biggest advantage of the Name property of the HttpMethodAttribute (which is the base class of HttpGetAttribute) is that you can distinguish method overloads:
[HttpGet(Name="ById"]
public IActionResult GetBy(int id)
{
}
[HttpGet(Name="ByExternalId"]
public IActionResult GetBy(Guid id)
{
}
So, this can contribute in the route selection.
EDIT: I've revised answer
The above sample code would result in an AmbiguousMatchException, where it is stating the same Template has been registered for different action.
I had put together another sample and used the following RouteDebugger to get insight. In the Configure method I've called the app.UseRouteDebugger() method to be able to see the registered routes in json format under the /route-debugger url.
[Route("api/[controller]")]
[ApiController]
public class TestController : ControllerBase
{
[HttpGet()]
public IActionResult GetA(string a)
{
return Ok(nameof(GetA));
}
[HttpGet(template: "GetB")]
public IActionResult GetB(string b)
{
return Ok(nameof(GetB));
}
[HttpGet(template: "GetC", Name= "GetD")]
public IActionResult GetD(string d, string e)
{
return CreatedAtRoute(routeName:"GetC", routeValues: new { c = "v"}, value: null);
}
[HttpGet(template: "GetC/{c}", Name = "GetC")]
public IActionResult GetC(string c)
{
return Ok(nameof(GetC));
}
}
The route table would look like this:
[
{
"Action":"GetA",
"Controller":"Test",
"Name":null,
"Template":"api/Test",
"Contraint":[{}]
},
{
"Action":"GetB",
"Controller":"Test",
"Name":null,
"Template":"api/Test/GetB",
"Contraint":[{}]
},
{
"Action":"GetD",
"Controller":"Test",
"Name":"GetD",
"Template":"api/Test/GetC",
"Contraint":[{}]
},
{
"Action":"GetC",
"Controller":"Test",
"Name":"GetC",
"Template":"api/Test/GetC/{c}",
"Contraint":[{}]
}
]
As you seen the following happened:
GetA method
It is exposed under the controller route because not Template has been specified.
The route itself does not have a Name so you can't refer to this route via its name inside ActionLink or CreatedAtRoute, etc.
GetB method
It is exposed under the api/test/getb, because the controller's and the action's Template properties are combined.
The route itself does not have a Name so you can't refer to this route via its name inside ActionLink or CreatedAtRoute, etc.
GetC method
It is exposed under the api/test/getc/{c}, because the controller's and the action's Template properties are combined. The c parameter can accept any value. If it is not provided then GetD will be called, because that was registered first.
The route has a Name (GetC) so you can refer to this route via its name inside ActionLink or CreatedAtRoute, etc. Like as we did it inside GetD
GetD method
It is exposed under the api/test/getc, because the controller's and the action's Template properties are combined. Because it was registered prior GetC method's route that's why it will called if no further path is provided.
The route has a Name (GetD). In the CreatedAtRoute we are referring to GetC via its name not through its route. If we are replacing the Name to GetC then it would throw the following exception at runtime:
InvalidOperationException: The following errors occurred with
attribute routing information:
Error 1: Attribute routes with the same name 'GetC' must have the same
template: Action: 'Controllers.TestController.GetD ()' - Template:
'api/Test/GetC' Action: 'Controllers.TestController.GetC ()' -
Template: 'api/Test/GetC/{c}
Summary
If you register two routes with the same Template it will throw an AmbiguousMatchException at runtime when you make a call against that route. (So, other routes will work perfectly fine)
If you register two routes with the same Name it will throw an InvalidOperationException at runtime when you make any call. (So, other routes will not work)
Route's Name provides the ability to refer them easily without knowing the exact Template. This separation allows us to change the Template without affecting referring links.
Name is the route name, as distinct from the template. See the docs page.
The docs state:
Route names can be used to generate a URL based on a specific route. Route names:
Have no impact on the URL matching behavior of routing.
Are only used for URL generation.
Route names must be unique application-wide.
You can use the name to generate URLs for named routes using IUrlHelper. For example, if you named a route "Konrad", you could generate a link like so:
string url = urlHelper.Link("Konrad", new { id = 5, query = "test" });
Where id and query are the route parameters.
By the way, the issue you had with the documentation is that HttpGet is an Attribute. The attribute syntax allows you to specify values for the attributes' properties by name after any positional constructor values.
Considering the following attribute, you can see that the constructor accepts int a, but there's also a string propery: B.
public class TestAttribute : System.Attribute
{
public TestAttribute(int a)
{
}
public string B {get;set;}
}
To use such an attribute, you could apply it in the following ways:
[TestAttribute(5)] // B is null
[TestAttribute(5, B = "hello")] // B is "hello"
or simply as Test:
[Test(5)] // B is null
[Test(5, B = "hello")] // B is "hello"
It says they can be used to generate a URL based on a specific route. I don't think I understand what it means (despite understanding the words as such). Please elaborate
Here are my two cents:
When designing a proper API, the level 3 of maturity model talks about HATEOAS constraint (Hypermedia As Transfer Engine Of Application State). More information about it can be found at : Maturity models of Rest API
In order to traverse through a resource and to know the actions that are available with that resource we generate links for the resource.
The generation of links is done with the help of URLHelper library, which takes in a name parameter to define the link. The name we associate with in the URLHelper library, is the name defined for HTTP GET/POST/PUT etc action using the attribute Name parameter.
In simple terms, it is an identifier for your Route.
P.S
A complete working example of a web api with HATEOAS can be found on github:
Web Api with HATEOAS example
After some searching, managed to find at least somewhat clear simple example with explanation, see section 5.5.2 here: https://livebook.manning.com/book/asp-net-core-in-action/chapter-5/254
The linked section contains two pieces of code, from which it is obvious, besides others already have mentioned:
You can have route template with parameters, and even provide template within Http verb template [Http...], but...
If needed to generate links to be returned to the client, to avoid some problems, it is easier to use the route name as explained here: https://csharp-video-tutorials.blogspot.com/2017/02/generating-links-using-route-names-in.html
About "URL generation", instead of hard-coded routes for certain API resources on the client side (e.g., details for the user with certain id value), Controller can send URL for each user, so the client doesn't need to have any logic about creating those URLs. Also, what about multimedia resources (images, videos, etc.), or any resources that have dynamically created URLs for protection purposes? Client side shouldn't know anything about how to construct those URLs, just obtain them from the Controller. In that way, it is not needed to have all URLs (or routes) predefined on both client and server side.
I think this and this could help.
Route name
The following code defines a route name of Products_List:
[ApiController]
public class Products2ApiController : ControllerBase
{
[HttpGet("/products2/{id}", Name = "Products_List")]
public IActionResult GetProduct(int id)
{
return ControllerContext.MyDisplayRouteInfo(id);
}
}
Route names can be used to generate a URL based on a specific route. Route names:
Have no impact on the URL matching behavior of routing.
Are only used for URL generation.
Route names must be unique application-wide.
Contrast the preceding code with the conventional default route, which defines the id parameter as optional ({id?}). The ability to precisely specify APIs has advantages, such as allowing /products and /products/5 to be dispatched to different actions.
In asp.net core source code I've found only this usage
[HttpGet("{id}", Name = "FindPetById")]
[ProducesResponseType(typeof(Pet), StatusCodes.Status200OK)]
[ProducesResponseType(StatusCodes.Status401Unauthorized)]
[ProducesResponseType(StatusCodes.Status404NotFound)]
public async Task<ActionResult<Pet>> FindById(int id)
{
var pet = await DbContext.Pets
.Include(p => p.Category)
.Include(p => p.Images)
.Include(p => p.Tags)
.FirstOrDefaultAsync(p => p.Id == id);
if (pet == null)
{
return new NotFoundResult();
}
return pet;
}
As pointed out here, having a double slash in a URL is valid.
I have an ASP Net Core project that uses attribute routing, a controller named GroupController for handling operations on Groups and an action for PUTting RuleParts of a group, specified by its ImportId of type string.
[Route("/api/[controller]")]
public class GroupController : ControllerBase
{
[HttpPut("{groupImportId?}/ruleParts")]
public async Task<IActionResult> PutRuleParts(string groupImportId, [FromBody]List<RulePartDto> ruleParts)
{
return null; //actual code ommitted for brevity
}
}
A URL like http://localhost/api/group/groupImportId/ruleParts matches as expected.
I would expect that null groupImportIds, i.e. URLs like http://localhost/api/group//ruleParts would call that same action, since the groupImportId route parameter has been marked as optional. However, when trying to call this URL, I get a 404 error and the action is not hit.
Is there a possibility to match an empty URL path segment in ASP Net Core?
Do not use the optional parameter in the middle of the route template.
Optional parameters are supposed to be used at the end of a URL. Routes won't match when optional parameters embedded in the middle segments are omitted as this will result in not found errors.
Instead attribute routing allows for multiple routes to be mapped to the same action.
[HttpPut("ruleParts")] // PUT api/group/ruleParts
[HttpPut("{groupImportId}/ruleParts")] //PUT api/group/123456/ruleParts
public async Task<IActionResult> PutRuleParts([FromBody]List<RulePartDto> ruleParts, string groupImportId = null) {
//...
}
The groupImportId argument of the action is made optional to allow the optional parameter to be omitted in the URL when the other route is requested.
Reference Routing to Controller Actions in ASP.NET Core
Why this doesn't work? I get error: System.InvalidOperationException: Multiple controller types were found that match the URL. This can happen if attribute routes on multiple controllers match the requested URL.
public class ConfigUpdateController: ApiController
{
[HttpPut]
[Route("api/device/{serial}/config")]
public IHttpActionResult Update(
[FromUri] string serial,
[FromBody] Configuration configuration)
{
}
}
public class ConfigQueryController: ApiController
{
[HttpGet]
[Route("api/device/{serial}/config")]
public IHttpActionResult Get(
[FromUri] string serial)
{
}
}
The reason why i want to have methods for same resource in separate controllers is decoupling queries from commands.
EDIT
To be honest, it's ample code to illustrate my problem, so please don't bother commenting controllers naming ect. It's not important in context of my question.
EDIT 2
I've found here web-api overview thet routing has 3 phases:
Routing has three main phases:
Matching the URI to a route template.
Selecting a controller.
Selecting an action.
So it seems this does not work because controller can't be resolved and method verb (PUT, GET) are not even checked? O_o
Read the error carefully, then look at your attribute routing. You have identical URLs for two different actions.
Program would have no idea which action to execute.
use [FromRoute] instead of [FromUri] annotations
I have Controller with some method GET :
public class TestController : ApiController
{
public List<T> Get(){...}
[ActionName("GetById")]
public T Get(int id){...}
}
Can i access second Get method as /Get?id=1 even if i have different ActionName?
ActionName for generating cache with different names
Updated because my previous answer was related to standard MVC controllers not Web API because that is what the ActionName attribute is for. I am not sure what if anything it would do on a web api controller. Without attributes or a change from the deault routing your actions would have the following routes "/api/test/" Get() "/api/test/id" Get(int id) where id is an int.
If you want more flexibility MVC5 supports attribute routing
In the event that a Controller specifies a route:
[Route("api/platypus/getPlatypi")]
public List<Platypus> GetAllPlatypi()
{
return _platypusRepository.GetPlatypi();
}
...is there any advantage to annotating it with a "[HttpGet]" like so:
[HttpGet]
[Route("api/platypus/getPlatypi")]
public List<Platypus> GetAllPlatypi()
{
return _platypusRepository.GetPlatypi();
}
?
For the example you have given there is not any advantage to adding the HTTP method attribute. By convention Web API will try to match a controller method that starts with the HTTP request method (GET, POST, PUT etc.).
In your example the method GetAllPlatypi will be considered for a match for all GET requests to that controller.
If however your method was named FindAllPlatypi you would need to add the [HttpGet] attribute to make it clear that this method is meant for GET requests.