What's the benefit of setting an alias for an action method using the "ActionName" attribute? I really don't see much benefit of it, in providing the user the option to call an action method with some other name. After specifying the alias, the user is able to call the action method only using the alias. But if that is required then why doesn't the user change the name of the action method rather then specifying an alias for it?
I would really appreciate if anyone can provide me an example of the use of "ActionName" in a scenario where it can provide great benefit or it is best to use.
It allows you to start your action with a number or include any character that .net does not allow in an identifier. - The most common reason is it allows you have two Actions with the same signature (see the GET/POST Delete actions of any scaffolded controller)
For example: you could allow dashes within your url action name http://example.com/products/create-product vs http://example.com/products/createproduct or http://example.com/products/create_product.
public class ProductsController {
[ActionName("create-product")]
public ActionResult CreateProduct() {
return View();
}
}
It is also useful if you have two Actions with the same signature that should have the same url.
A simple example:
public ActionResult SomeAction()
{
...
}
[ActionName("SomeAction")]
[HttpPost]
public ActionResult SomeActionPost()
{
...
}
I use it when the user downloads a report so that they can open their csv file directly into Excel easily.
[ActionName("GetCSV.csv")]
public ActionResult GetCSV(){
string csv = CreateCSV();
return new ContentResult() { Content = csv, ContentEncoding = System.Text.Encoding.UTF8, ContentType = "text/csv" };
}
Try this code:
public class ProductsController
{
[ActionName("create-product")]
public ActionResult CreateProduct()
{
return View("CreateProduct");
}
}
It is also helpful when you need to implement method overloading.
public ActionResult ActorView()
{
return View(actorsList);
}
[ActionName("ActorViewOverload")]
public ActionResult ActorView(int id)
{
return RedirectToAction("ActorView","Home");
}
`
Here one ActorView accepts no parameters and the other accepts int.
The first method used for viewing actor list and the other one is used for showing the same actor list after deleting an item with ID as 'id'.
You can use action name as 'ActorViewOverload' whereever you need method overloading.
This class represents an attribute that is used for the name of an action. It also allows developers to use a different action name than the method name.
Related
I am working with a BaseController that is used for a variety of entities. They may have int or string primary keys, represented by <TPk>.
E.g.:
[HttpGet]
public ActionResult Create(TPk id)
{
return View();
}
Everything is fine until I try and use TPk as an optional parameter.
[HttpGet]
public ActionResult Create(TPk id = default(TPk))
{
return View();
}
It seems that the 'optional' part isn't working.
So /controller/create/2 is fine, but /controller/create gives me the following error:
The parameters dictionary contains a null entry for parameter 'id' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult Create(Int32)'
The optional works fine with an int or string id. I can call /controller/create/2 AND /controller/create.
But using a generic type argument TPk, the parameterless route no longer works.
What I've Tried
I have tried making the TPk parameter nullable, but it won't compile:
The type 'TPk' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'Nullable'
I have tried changing the parameter name from id to altId as per this question - no joy
I have tried calling the same method, in exactly the same way, but with non-generic parameters. E.g.:
public virtual async Task<ActionResult> Create(int id = default(int))
This worked fine.
I have tried creating a simple new project to isolate this code. (Shown below). This still gives problems with the parameterless version.
Simple Code Test
Controller
public abstract class BaseController<TPk> : Controller
{
public ActionResult Create(TPk id = default(TPk))
{
return View();
}
}
public class NewsController : BaseController<int>
{
}
Entity Classes
public class BaseDataModel<TPk>
{
public TPk Id { get; set; }
public string Title { get; set; }
}
public class PageDataModel : BaseDataModel<string>
{
public string Content { get; set; }
}
public class NewsDataModel : BaseDataModel<int>
{
public DateTime Date { get; set; }
}
Asp.net conventions are heavily based on reflection. So this might explain the behavior. I have not tested if it realy does not work, but I am sure at this state you already tried to create a new project (POC) to preclude any custom code.
Maybe it can be fixed by looking deeper into the routing (method selection) and ModelBinder source code...
I would just create a different DuplicateRecord action instead.
If you do not understand your method without this comment, it is a good indication, that your current code probably smells anyway. (You are doing to much at the same thing):
// duplicates existing record if id is passed in, otherwise from scratch
Extract the shared things to another method (maybe even a service class) and have for each difference a seperate method.
That said, the idea of a generic CrudController is lovely, I tried this myself some years ago. But in trying so I have introduced all sort of generic parameters, strategy patterns, event delegates to make all possibilities possible.
What happens if you need a join?
What happens if you need a transaction?
How do you handle errors?
What happens if your crud logic needs 1, 2, 3 ... additional parameters to decide what to do?
Soft Delete / Hard Delete?
Cascade Delete / Restrict Delete?
What happens if you ...
I have written so much code, it was blessing to revert to the good old non generic code. And if abstracted away in a service, the ActionMethods realy do not need to get big.
public async Task<IActionResult> CreateProduct(CancellationToken ct, ProductCreateModel model)
{
var result = await _productService.CreateAsync(model, ct);
//create response with some helpers... probably some ActionFilters
}
Generics can work ofcorse in a simple crud mapping where each View has exact one Entity, but it does not scale very well. So beaware and think twice about what you realy want ;)
I have asp.mvc project. Currently routing is set to form following url's:
site/school/45
site/school/45/courses
site/school/45/teachers
site/school/45/courses/17
etc.
I want to change this '45' (id of the school) to more 'user friendly' name, for example to take 'Name' of school '45'.
Now action methods are like:
public ActionResult Index(int schoolId)
{ ...
Is it possible to change routing to display school name instead schoolID without changing action methods?
"without changing action methods" seems to be the most important part of your question, right?
Yes, you can. You may override OnActionEcecuting(ActionExecutingContext filterContext) method in your controller class to do name-id mapping for you. You need to do the following:
Implement base controller class, something like this:
public class BaseController: Controller
{
protected override void OnActionExecuting(ActionExecutingContext filterContext)
{
base.OnActionExecuting(filterContext);
var shoolName = filterContext.RouteData.Values["schoolName"].ToString();
var schoolId = ...; // Get school id from name somehow here
filterContext.RouteData.Values.Add("schoolId", schoolId);
}
}
(I assume here that you will change your corresponding routing parameter name from schoolId to schoolName in Global.asax.cs / RegisterRoutes).
Update all your controllers by making them inherit not from Controller but from BaseController, like this:
public class SomethingController: BaseController
{
...
}
After that everything should be working. You won't need to change your controller actions - schoolId parameter will be already at place when it will come to calling them.
You will need to add a new route to the global routing to allow for a string name rather than just an int id.
The best option would be to create a new method that takes the school name and then (from the database or a cached object/dictionary) translates the name to the id then forwards to the int index method.
Something like this (not shown caching)
public ActionResult Index(string schoolName)
{
var schoolId = SomeMethodThatGetsTheIdFromString(schoolName)
RedirectToAction("Index", new { id = schoolId });
}
You could achieve this with a custom model binder to figure out the id of the school based on the name and use this to 'bind' to your schoolId parameter.
However, I would suggest leaving your routing the way it is - if a school's name changes for example it would mean that all bookmarks would no longer work, or your url would appear incorrect.
Wanted to use the same URL for a GET/PUT/DELETE/POST for a REST based API, but when the only thing different about the Actions is which HTTP verbs it accepts, it considers them to be duplicate!
"Type already defines a member called 'Index' with the same parameter types."
To which I said, so what? This one only accepts GET, this one only accepts POST... should be able to be co-exist right?
How?
That's not ASP.NET MVC limitation or whatever. It's .NET and how classes work: no matter how hard you try, you cannot have two methods with the same name on the same class which take the same parameters. You could cheat using the [ActionName] attribute:
[HttpGet]
[ActionName("Foo")]
public ActionResult GetMe()
{
...
}
[HttpPut]
[ActionName("Foo")]
public ActionResult PutMe()
{
...
}
[HttpDelete]
[ActionName("Foo")]
public ActionResult DeleteMe()
{
...
}
[HttpPost]
[ActionName("Foo")]
public ActionResult PostMe()
{
...
}
Of course in a real RESTFul application the different verbs would take different parameters as well, so you will seldom have such situations.
You may take a look at SimplyRestful for some ideas about how your routes could be organized.
While ASP.NET MVC will allow you to have two actions with the same name, .NET won't allow you to have two methods with the same signature - i.e. the same name and parameters.
You will need to name the methods differently use the ActionName attribute to tell ASP.NET MVC that they're actually the same action.
That said, if you're talking about a GET and a POST, this problem will likely go away, as the POST action will take more parameters than the GET and therefore be distinguishable.
So, you need either:
[HttpGet]
public ActionResult ActionName() {...}
[HttpPost, ActionName("ActionName")]
public ActionResult ActionNamePost() {...}
Or:
[HttpGet]
public ActionResult ActionName() {...}
[HttpPost]
public ActionResult ActionName(string aParameter) {...}
Another option is to have a single method that accepts all and distinguishes between HttpMethod and calls the appropriate code from there. E.g.
string httpMethod = Request.HttpMethod.ToUpperInvariant();
switch (httpMethod)
{
case "GET":
return GetResponse();
case "POST":
return PostResponse();
default:
throw new ApplicationException(string.Format("Unsupported HttpMethod {0}.", httpMethod));
}
As a workaround you can add to one of the methods an extra argument with a default value, just to bypass the limitation and be able to build.
Of course take in mind that this is not the most recommended way of doing things, and also you will have to make clear in your code (by the parameter name or via comments) that this is an extra argument just to allow it to build, and of course make sure that you have decorated your attributes correctly.
I have the following scenario: my website displays articles (inputted by an admin. like a blog).
So to view an article, the user is referred to Home/Articles/{article ID}.
However, the user selects which article to view from within the Articles.aspx view itself, using a jsTree list.
So I what I need to do is to be able to differentiate between two cases: the user is accessing a specific article, or he is simply trying to access the "main" articles page. I tried setting the "Articles" controller parameter as optional (int? id), but then I am having problems "using" the id value inside the controller.
What is the optimal manner to handle this scenario? Perhaps I simply need a better logic for checking whether or not an id parameter was supplied in the "url"?
I am trying to avoid using two views/controllers, simply out of code-duplication reasons.
Use separate actions, like:
public ActionResult Articles() ...
public ActionResult Article(int id) ...
Alternatively move it to an Articles controller (urls using the default route will be: Articles and Articles/Detail/{id}):
public class ArticlesController : Controller
{
public ActionResult Index() ...
public ActionResult Detail(int id) ...
}
If you still must use it like you posted, try one of these:
public ActionResult Articles(int id = 0)
{
if(id == 0) {
return View(GetArticlesSummaries());
}
return View("Article", GetArticle(id));
}
public ActionResult Articles(int? id)
{
if(id == null) {
return View(GetArticlesSummaries());
}
return View("Article", GetArticle(id.Value));
}
First of all, I agree with #Steve :). But if you really want to use
int? id
you can just check in your controller method if the id is set using a simple
if(id == null)
and if so, load all articles from your DB (or something alike) and pass these to your view (either directly, or by using a view model). If the id is set you just load the article having that id from your DB and send that to the view (possibly in a list as well if you dont use view models)?
Than in your view just load all articles in the list with articles supplied to the view. Which contains either all or just one.
Complete dummy code
public ActionResult showArticles(int? id){
List<Articles> aList;
if(id == null){
aList = repository.GetAllArticles().ToList();
}else{
aList = new List<Articles>();
aList.add(repository.GetArticleByID(id));
}
return View(aList);
}
Your View has something like:
<% Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master"
Inherits="System.Web.Mvc.ViewPage<List<Articles>>"%>
foreach(Articles a in Model)
//display article
And you call it using either of the next two options:
html.ActionLink("one article","showArticles","Articles",new {id = aID},null}
html.ActionLink("all articles","showArticles","Articles"}
Define a default value for the Id that you know indicated no value was supplied - usually 0.
public ActionResult Articles([DefaultValue(0)]int Id)
{
if (Id == 0)
// show all
else
// show selected
..
The easiest solution is to have two different actions and views but name the actions the same.
public ViewResult Articles()
{
//get main page view model
return View("MainPage", model);
}
public ViewResult Articles(int id)
{
// get article view model
return View(model);
}
this to me sounds like two separate pages and should be treated as such. You have the "Main" view page and the "articles" page.
I would split it into two actions. They should not be much dupliation at all really, both should be doing a call to get the same ModelView and the article will simply get the a extension to that!
I don't know if you tried this, but instead if you are typing the value directly into the URL, then, instead of passing it like this:
controller/action/idValue
try passing it like this:
controller/action?id=value
Make the parameter required then set a default value in the routing that is a value that isn't a valid index and indicates to your action that it should render the main page.
Well, this is the combined solution I am using:
Using same controller, with DefaultValue:
public ActionResult Articles([DefaultValue(0)]int id)
If DefaultValue was used, I refer to "MainArticles" view. If an article ID was provided - I refer to the "Articles" view with the appropriate article passed inside the ViewModel.
In both cases the ViewModel is populated with the data both views need (complete article and category lists).
Thanks everyone for your help!
I've created a routing structure whereas the action part of the URL serves as a dynamic handler for picking a specific user created system name. i.e.
http://mysite.com/Systems/[SystemName]/Configure, where [SystemName] designates the name of the system they would like to configure.
The method that routes the system is the following:
public ActionResult Index(string systemName, string systemAction)
{
ViewData["system"] = _repository.GetSystem(systemName);
if (systemAction != "")
{
return View(systemAction);
}
else
{
// No Id specified. Go to system selection.
return View("System");
}
}
The above method sets the system to configure and routes to a static method where the view is displayed and a form awaits values.
The question I have is that when I create my configuration view, I lose my posted values when the form is submitted because it routes back to the above Index controller. How can I determine if data is being posted when hitting my above Index controller so that I can make a decision?
Thanks!
George
Annotate the controller method that handles the POST like this:
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Index(string systemName, string systemAction)
{
// Handle posted values.
}
You can have a different method in your controller that handles the GETs:
[AcceptVerbs(HttpVerbs.Get)]
public ActionResult Index(string systemName, string systemAction)
{
// No posted values here.
}
Note that, although I have copied the same method and parameters in each case, the signature for the second method (parameters and types) will have to be different, so that the two methods are not ambiguous.
The NerdDinner tutorial has examples of this.