Is there any danger to use one of the 2 following methods? Is there any best practice?
I'm wondering if I will hit a wall when there will be many user online at the same time on the website.
Storing Model in Session for later reuse
public ActionResult Index()
{
var model = new Model();
Session["Model"] = model;
return View(model);
}
[HttpPost]
public ActionResult Index(FormCollection fc)
{
var model = (Model)Session["Model"];
//Update stuff
return View(model);
}
Recreating it on every requests
public ActionResult Index()
{
var model = new Model();
return View(model);
}
[HttpPost]
public ActionResult Index(FormCollection fc)
{
var model = new Model();
//Update stuff
return View(model);
}
Each model :
might contain a lot of calls to the database (it can take some time to
initialize them)
might contain list of information (a lot of data)
Edit
Feels like most avoid trying to answer the question and got stuck on unimportant details to the question.
I accepted the only answer which was able to stay on topic.
Atavari answer is completely off topic and didn't understood the question at all.
Both of those methods are wrong. Your post action should receive the model, not a FormCollection object.
[HttpPost]
public ActionResult Index(Model model)
{
//Update stuff
return View(model);
}
And, you usually redirect to a different page after the Add/Update is successful, and only return the same View if there's validation error. So, your post action should look more like this:
[HttpPost]
public ActionResult Index(Model model)
{
if(ModelState.IsValid)
{
//Update stuff
//return to a different page or whatever needs to be done
//after a successful update
}
// If model is not valid...
return View(model);
}
UPDATE:
If there are properties in your model that are not posted to your action (like a SelectList for a dropdown), you'll only need them if you want to return the same View (normally when there's validation error). In that case you don't have to recreate your model. You just repopulate those properties.
Let's say your model has a property called Items. This is how your actions should look like:
public ActionResult Index()
{
var model = new Model();
model.Items = GetItems();
return View(model);
}
[HttpPost]
public ActionResult Index(Model model)
{
if(ModelState.IsValid)
{
//Update stuff
//return to a different page or whatever needs to be done
//after a successful update
}
// If model is not valid...
model.Items = GetItems();
return View(model);
}
It depends on how many users you really have. Using session can be comfortable and easy but scalability may become an issue.
If you use it just to improve performance, I would suggest you to use cache instead. Take care that objects in cache can expire so you have always to check whether they are still there. Cache is better than session because it is self optimized. If memory gets low it's automatically cleaned, while session variables are never cleaned (unless of course when session expires).
Related
ActionResult is the base class for the various return types to View in MVC. So your action must return an ActionResult or a class derived from it in order to work.
so we can use
public ContentResult Index()
{
return Content("Hello world");
}
or for example
public ViewResult Index()
{
return View();
}
or ActionResult
public ActionResult Index()
{
if (ViewBag.Hello = "World")
return Json("");
return PartialView();
}
BUT also is possible use string !!!
public string Index()
{
return "Hello World";
}
WHY is than not possible return integer to view? (Or maybe it is?)
public int Index()
{
return 4;
}
and not possible return some entity to view (Or maybe it is?)
public User Index()
{
return new User();
}
My question is : What happening behind scene when we want to render view?
I agree that this is quite a broad question, but I wanted address and answer a few of the points you raised in your question.
You can return an int, string or object from your action method and it will simply return the object's string representation as the result.
Therefore you don't have to return an object of type ActionResult in order for it to work, but the ActionResult enables useful functionality through it's various implementations so that ASP.NET MVC Framework can handle different scenarios straight out of the box.
Such as returning views and handling the ViewModel you want to pass to your view:
return View(); // Default view without view model
return View(viewModelObject); // Default view with a view model
Returning views based on your routing information:
return View("viewName", viewModelObject);
Performing redirects to another page, using your routing information:
return RedirectToAction(actionName, controllerName);
Returning a page with specific status codes:
return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
Returning JSON instead of a view:
return JsonResult(myObject);
All of the above examples do different things, return different types of results and handle your objects for you so that you don't have to code the behaviour yourself - they're ready for you to use.
Another handy thing is that you can create your own implementations of ActionResult to create your own behaviour, so it's very flexible in that regard.
I agree with #Daniel J.G. that you should do some more reading on how ASP.NET MVC hangs together and it will become a lot more clear to you.
I'm having some issues with my DropDownLists, because when I post the information and my Model is not valid it comes back "empty" to the page triggering an error exactly like this question.
I've used the solution proposed there and it fixed my problem. Anyway, I wanted to avoid querying the database every time my ModelState is not valid and I came with this approach. I would like to know if it is valid or if there are better ways to do it now, considering that instead of MVC2 (which was the MVC version from the question) I'm now using MVC 5, maybe they added something new to tackle this.
What I've done was to use the TempData to persist the information when my model is not valid.
public class ViewModel
{
[DisplayName("Project")]
public int ProjectID { get; set; }
public List<SelectListItem> Projects { get; set; }
//Other fields
}
Now my Create() Action (that populates Projects)
[HttpGet]
public ActionResult Create()
{
ViewModel vmodel = new ViewModel();
vmodel.Projects = db.GetProjects(User.Identity.Name).Select(x => new SelectListItem { Text = x.Description, Value = x.Id }).ToList();
TempData["Projects"] = vmodel.Projects;
return View(vmodel);
}
And my post would be like this:
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(ViewModel vmodel)
{
//Clear TempData (in theory will clear my tempdata when read, so if this controller redirects to another action my tempdata will be clear)
List<SelectListItem> projects = (TempData["Projects"] as List<SelectListItem>);
if (ModelState.IsValid)
{
//...
}
//If it got here it's going back to the screen.
//Repopulate the TempData (allowing it to exist one more trip)
TempData["Projects"] = projects;
vmodel.Projects = projects
return View(atendimento);
}
Is this approach a good one? Is there a better way to achieve that without querying the database every single time?
Thanks a lot!
You don't need to use TempData at all as you have a property in your view model to hold the dropdown items.
public ActionResult Create()
{
ViewModel vmodel = new ViewModel();
vmodel.Projects = GetProjects();
return View(vmodel);
}
private List<SelectListItem> GetProjects()
{
return db.GetProjects(User.Identity.Name)
.Select(x => new SelectListItem { Text = x.Description,
Value = x.Id }).ToList();
}
And in the view
#Html.DropDownListFor(s=>s.ProjectID,Model.Projects)
And in your HttpPost action, If ModelState is not valid, Reload the Projects collection again (because http is stateless)
if(ModelState.IsValid)
{
// to do :Save and redirect
}
model.Projects = GetProjects();
return View(model);
You may cache the Projects so that you do not need to hit the database every time, if you are too much worried about performance.
Personally, I wouldn't worry about querying the database each time for this kind of operation.
What if projects are added/deleted? This could be the reason the save failed (selected project deleted) and the user would never realise it.
I usually write a method to populate all of my view model's SelectListItems and then use this in my Get and in my Post if the validation fails.
In an MVC4 project I need to "refresh" the page depending on some messages that can be present, otherwise I just redirect to a page, and if presenting again the page if them messages are present I would like to avoid just returning the View as it will cause then the double submission when the user tries to refresh it.
What I'm trying to do is this
[HttpGet]
public ActionResult SampleMethod()
{
viewModel = _builder.Build();
return View(viewModel);
}
[HttpPost]
public void SampleMethod(SampleViewModel viewModel)
{
if (ModelState.IsValid)
{
var response = serviceCall;
var errorMessages = response.ErrorMessages;
if (!errorMessages.Any())
{
//Redirect to proper view
}
else
vm = _builder.Build();
}
else vm = _builder.Build(); //There is some validation error I rebuild
CashbackOffersConfirmation(vm);
}
public ActionResult SampleMethodConfirmation(SampleViewModel viewModel)
{
return View("SampleMethod", viewModel);
}
It goes through the process
but the final page is .../SampleMethod instead of .../SampleMethodConfirmation and is blank,
Is this something to do with the routing (quite lost in this)? Is this a correct approach?
Thanks
In order to pass the object model from the view to the controller, you need to make a post request. Make sure you use a form that will generate the post request.
Also make the SampleMethodConfirmation method a post.
E.g.: add [HttpPost] on top of the method in the controller
Warning: This is my first web app.
I have 4 models, views and controllers. Lets call them A, B, C, D(ex. ModelA, ControllerA, ViewA). They are all basic views with list scaffolding.
/ControllerA/Index
User starts at ViewA and Selects an the first item, which redirects the user to ViewB
/ControllerB/Function?Aid=1
ViewB shows another list based on Selection from ViewA. Then the user Selects again is is redirected to ViewC
/ControllerC/Function?Aid=1&Bid=2
ViewC shows another list based on Selections from ViewA and ViewB. Then the user Selects again is is redirected to ViewD.
/ControllerD/Function?Aid=1&Bid=2&Cid=3
ViewD shows another list based on Selections from ViewA, ViewB, and ViewC, Then the user Selects again.
At this point I would like to POST Aid, Bid, Cid, and Did and save them in my database. Ideally the user would click the link, the data would be posted and then the site would redirect the user back to the homepage. Should I create another model and controller to Handle the post? I thought about trying to do the POST from controllerD but that doesn't seem like the proper way to do this.
The msdn tutorials only show posting directly from a view with a strongly typed model. I kinda stuck and I would prefer not to make this a complete mess.
Edit for Code
Controller
public ActionResult myFunction(int Aid = 0, int Bid, int Cid)
{
//query D stuff here
if (D == null)
{
return HttpNotFound();
}
return View(D.ToList());
}
[HttpPost]
[InitializeSimpleMembership]
public ActionResult CreateQuote(int Aid, int Bid, int Cid, int Did)
{
Quote myQuote = new Quote();
myQuote.Customer_ID_FK = (int)Membership.GetUser().ProviderUserKey;
myQuote.A_ID_FK = Aid;
myQuote.B_ID_FK = Bid;
myQuote.C_ID_FK = Cid;
myQuote.D_ID_FK = Did;
if (ModelState.IsValid)
{
db.Quotes.Add(myQuote);
db.SaveChanges();
db.Quotes.Max();
int mymax = db.Quotes.Max(q => q.ID);
return RedirectToAction();
}
return View(D.ToList());
}
[HttpPost]
[InitializeSimpleMembership]
public ActionResult CreateQuote(Quote myQuote)
{
myQuote.Customer_ID_FK = (int)Membership.GetUser().ProviderUserKey;
if (ModelState.IsValid)
{
db.Quotes.Max();
int mymax = db.Quotes.Max(q => q.ID);
db.Quotes.Add(myQuote);
db.SaveChanges();
return RedirectToAction();
}
return View(D.ToList());
}
It usually makes sense to put your post handler in the controller it's related to. This isn't always the case, as sometimes it would make more sense to make a new controller to handle all posts related to a certain task. You should also understand the distinction between a method IN a controller, and a controller. A controller is just a class that inherits from System.Web.Mvc.Controller and can have methods just like any other class. A perfectly reasonable controller could look like this:
public class DController : Controller
{
//GET /d
public ActionResult Index()
{
//MyModel is a class that would contain the logic to display
//the selections from A, B, and C
var model = new MyModel();
return View(model);
}
//POST /d/saveresults
//We only want this method to accept POST
[HttpPost]
public ActionResult SaveResults(MyEntity data)
{
var model = new MyModel();
model.SaveResultsToDatabase(data);
return Redirect("/");
}
}
The important thing in a controller is to keep logical processing to a minimum. There's nothing wrong with having an if statement here and there, but the majority of your logic should be handled by your model. A controller is there primarily to pass data between your views and models.
I am fairly new to MVC and i'm looking for advice on how to setup a particular registration controller.
I have a controller called AccountController which has a Register method and I have a Register.cshtml.
Now, one of the biggest problems I seem stuck on is that I have 2 dropdowns that I need to populate based on the response from a service as these values change depending on location and other various parameters.
I have my page started and loading but I'm not sure what to do once a user click 'register'.
#model Adw.Models.RegisterModel //This is my model
#Html.DropDownListFor(m => m.States, new SelectList(Model.States)); // I load my dropdowns here
[AllowAnonymous]
public ActionResult Register(RegisterModel model)
{
model.States = Services.GetStates().Payload;
model.Countries = Services.GetCountries().Payload;
return View(model);
}
So my question is, when a user submits the form, should it come back to this same method? If so what would be the best way to validate that this is a submit rather than an initial load?
Also i haven't done much in the way of error handling and could use a suggestion on that, such as if either of the above service calls fail, then a registration cannot be completed, should that direct to a new page or is there a easy way to build that kind of error into the same page?
You should create two different method. One for GET and second for POST request:
[AllowAnonymous]
[HttpGet]
public ActionResult Register()
{
...
}
[AllowAnonymous]
[HttpPost]
public ActionResult Register(RegisterModel model)
{
if (ModelState.IsValid)
{
// create user
return this.RedirectToAction("SignIn");
}
else
{
return View(model);
}
}
You can review sample from default template.