ModelBinding a generic type in MVC3 - asp.net-mvc

In my views I'm using a generic type for the Model, ItemModel<T>.
This allows me to have a basetype on my model and it works fine. Within ItemModel<T> I attach the actual entity of T to a property called 'Item'.
Let's say I'm loading a User item: in my view I would like to do something like this:
<%: Html.TextBoxFor(Model => Model.Item.NickName,
new { id="NickName", name="NickName" })%>
Because the entity is added via the Item property, this generates the input tag's name attribute as 'Item.NickName'. When posting, MVC can no longer relate this to the User.NickName property of the user object in my controller
public ActionResult Login(User user, string redirectUrl)
and therefore nothing gets loaded into my User object. Is there a way to fix this? I've been looking into writing a custom bindingmodel or valueprovider, but that looks like alot of work for something this simple. Plus, I'm really not sure if that's that way to go.
All help is greatly appreciated!

change method of your actionresult from
public ActionResult Login(User user, string redirectUrl)
To
public ActionResult Login(User Item, string redirectUrl)
this way modelbiner will be able to locate properties of User object prefixed with Item

you can create your helper methods to create that textbox
public static MVCString MyTextBox<T>(this HtmlHelper html,T _item,String PropertyName)
{
TagBuilder myTag = new TagBuilder("input");
myTag.Attributes("type")="Text";
myTag.Attributes("id")=PropertyName;
myTag.Attributes("name")=PropertyName;
myTag.Attributes("value")=typeof(_item).GetProperty(PropertyName).GetValue(_item,null).toString();
Return MvcHtmlString.Create(selectTag.ToString())
}

Related

MVC - Inherited view model members [duplicate]

My Post call does not return the correct Model type. It always use the baseObject instead of the correct derived object that I passed in from the Get
RestaurantViewModel.cs
public class RestaurantViewModel{
public Food BaseFoodObject{get;set;}
}
Food.cs
public class Food{
public string Price{get;set;)
}
Bread.cs -- Inherit from Food
public class Bread:Food{
public int Unit{get;set;}
}
Milk.cs -- Inherit from Food
public class Milk:Food{
public string Brand{get;set}
}
Editor For Template for Bread. Display the unit and allow user to edit
Index.html
#Model RestaurantViewModel
#using(Html.BeginForm("SaveFood", "Food"))
{
#Html.EditorFor(m=>m.BaseFoodObject)
<input type="submit" value="Process"/>
}
Bread.cshtml
#Model Bread
<div>
#Html.TextboxFor(bread=>bread.Unit)
</div>
FoodController.cs
public ActionResult Index(){
Bread bread = new Bread(){
Price = "$10",
Unit = 1
}
RestaurantViewModel viewModel = new RestaurantViewModel(){
BaseFoodObject = bread
}
return View(viewModel);
}
public ActionResult Post(RestaurantViewModel viewModelPost)
{
// When I inspect the viewModelPost, there is no attribute for unit
}
Final Result:
1. The display looks correct. EditorFor is smart enough to pick the correct editor template and display the value correctly
2. The Save does not work. The Unit attribute of Bread Object does not get passed in with the RestaurantViewModel. The reason for that is the RestaurantViewModel used the Food object instead of Bread
I hope there is away to modify the EditorFor and tell it to use the Model in the View or the Object Type that I passed in when I display it.
Thanks
Update 1: I solved this problem by using the custom binder and using a factory to decide which object I really want. This helps construct the correct Model which I want
MVC is stateless. A couple of references.
There's a couple of statements in your question that conflict with this, and how MVC binding works eg:
My Post call does not return the correct Model type.
Possibly just terminology, but your Post call does not 'return a model type' - it goes into the model that's defined in the post action, in this case RestaurantViewModel.
instead of the correct derived object that I passed in from the Get
because it is stateless, it knows nothing about the model you passed in from the get... absolutely nothing.
The final html rendered via the getaction+view.cshtml+model is not linked to the postaction. You could just as easily take the rendered html, save it, reboot your PC, reload the rendered html and it will work exactly the same way.
a way to modify the EditorFor and tell it to use the Model in the View or the Object Type that I passed in when I display it
When you use EditorFor it sets an ID and name attribute based on the model it was bound to, so it already does this, but perhaps you are not binding to the model you want to bind to to get the correct id.
So, to the question, if, in 'normal' C# code you were to instantiate a new instance of RestaurantViewModel, what would you expect the type of BaseFoodObject to be?
This is what the ModelBinder is doing - it's creating a new RestaurantViewModel.
As your post action method's signature does not include anything to do with Bread - all the bread properties are ignored.
Some options:
Check for the food properties after binding and read them manually (probably the quickest+easiest but not very "mvc-ish")
public ActionResult Post(RestaurantViewModel viewModelPost)
{
if (!string.IsNullOrEmpty(Request.Form["Unit"]))
// it's a bread form
to make this easier, you could provide a hidden field with the type
if (Request.Form["Type"] == typeof(Bread).Name)
{
var bread = new Bread { Unit = Request.Form["Unit"] }
Add bread to the action so it's bound
public ActionResult Post(RestaurantViewModel viewModelPost, Bread bread)
but then, obviously, it won't work for milk.
So could extend this using an ActionNameSelector to select the correct action
public ActionResult PostBread(RestaurantViewModel viewModelPost, Bread bread)
public ActionResult PostMilk(RestaurantViewModel viewModelPost, Milk milk)
[AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
public sealed class FoodSelectorAttribute : ActionNameSelectorAttribute
{
public override bool IsValidName(ControllerContext controllerContext, string actionName, MethodInfo methodInfo)
{
... check if provided parameters contains bread/milk
(related link but not a solution to this specific case)
Another option might be to change the Restaurant type to a generic, but would require a few more changes (and ideally use of interfaces), and more details (provided here as an idea, rather than a solution)
The basics would be:
public class RestaurantViewModel<T>
where T: Food
{
}
public ActionResult Post(RestaurantViewModel<Bread> viewModelPost)
public ActionResult Post(RestaurantViewModel<Milk> viewModelPost)
but I've not confirmed if the default ModelBinder would work in this case.
The problem comes with the post. Once you post, all you have is a set of posted data and a parameter of type, RestaurantViewModel. The modelbinder sets all the appropriate fields on Food because that's all it knows. Everything else is discarded. There's nothing that can be done about this. If you need to post fields related to Bread then the type of your property must be Bread. That's the only way it will work.

Create and assign value back from View bag to Text box in MVC

I have to create a textbox from a viewbag property in MVC. I could do the mapping like #Html.TextBox("Comments", (string)ViewBag.Comments) but how do I read it back when the page is posted to the server. It is not filling the viewbag property back. I am very new to MVC so maybe don't understand the concept totally .
Thanks
Your ViewBag wont get updated from your view and that is not the way to get data from your form. Rather, you should either use strongly typed model binding to read your data from your Action Method or you can simply check for the key in your Forms data. I am showing you example for both:
Example 1: Strongly typed model binding.
[HttpPost]
public ActionResult MyAction(string comments)
{
// the Comment from the text box.
return View();
}
Example 2: Reading from Posted Data:
[HttpPost]
public ActionResult MyAction()
{
// the Comment from the text box.
string comments = Request.Form["comments"];
return View();
}
I hope, you will like to use the Example 1.
Anyway, the best practice would be to bind your View with a Model class and use HtmlHelper for generating the text box like :
Html.EditorFor(model => model.Comments)
Where your Model class contains a property named Comments.
And your action method should accept the same Model type as argument. Here is an example:
[HttpPost]
public ActionResult MyAction(MyModel model)
{
string comments = model.Comments;
}
And you should bind your View with the model of type MyModel.
I can understand that, as you are new to MVC, this may not make clear sense now, so, I would suggest you to check out some basic MVC tutorial. You can start from here : http://www.asp.net/mvc/tutorials

MVC sending data from View to Controller

I am quite new to MVC 3.
I know how to send a strongly typed object from a Controller to a View. What I have now, is a View which contains a table/form which consists of that data.
The user can change that data whilst they're are in that View (html page).
When they click on "Save", how do I send the data from the View back to the Controller so that I can update my database.
Do I overload the Controller method so that it accepts a parameter of the model type? Can you please provide some source code.
(Please do not show code of persisting data to a database, I know how to do that part).
Thank you very much for helping me.
I would also prefer using #Html.BeginForm()
I like creating an action method made for my post data. So let's say you have a UserViewModel:
public class UserViewModel
{
public int Id { get; set; }
public string Name { get; set; }
}
Then a UserController:
public class UserController
{
[HttpGet]
public ActionResult Edit(int id)
{
// Create your UserViewModel with the passed in Id. Get stuff from the db, etc...
var userViewModel = new UserViewModel();
// ...
return View(userViewModel);
}
[HttpPost]
public ActionResult Edit(UserViewModel userViewModel)
{
// This is the post method. MVC will bind the data from your
// view's form and put that data in the UserViewModel that is sent
// to this method.
// Validate the data and save to the database.
// Redirect to where the user needs to be.
}
}
I'm assuming you have a form in your view already. You'll want to make sure that the form posts the data to the correct action method. In my example, you'd create the form like so:
#model UserViewModel
#using (Html.BeginForm("Edit", "User", FormMethod.Post))
{
#Html.TextBoxFor(m => m.Name)
#Html.HiddenFor(m => m.Id)
}
The key to all this is the model binding that MVC does. Make use of the HTML helpers, like the Html.TextBoxFor I used. Also, you'll notice the top line of the view code I added. The #model tells the view you'll be sending it a UserViewModel. Let the engine do work for you.
Edit: Good call, did that all in Notepad, forgot a HiddenFor for the Id!
In MVC, the act of scraping out data from POST or GET HttpRequests is referred to as Model Binding - there are plenty of SO questions relating to this.
Out of the box, MVC will bind your Get and Post variables based on convention, e.g. a form field with the name 'FormName' will be bound back to a parameter on your controller with the same name.
Model binding also works for objects - MVC will instantiate an object for your controller, and set the properties with the same name as your form.

mvc.net how to edit member list variables

Given the following model which has a name, url, and an arbitrary list of keywords (I want the user to add a series of keywords) ...
public class Picture
{
public Picture()
{
keywords = new List<string>();
}
public string name {get;set:}
public string url {get;set;}
public List<string> keywords{get;set;}
}
... and the following action in my controller ...
[HttpPost]
public ActionResult Edit(FormCollection fc)
{
if (ModelState.IsValid)
{
// do stuff
}
return View(ModelManager.Picture);
}
In the FormCollection I have the following field
fc["keywords"] = "keyword1,keyword2,keyword3"
And I then create a Picture object based on the form collection.
However, I would prefer to use a strongly-typed action such as
[HttpPost]
public ActionResult Edit(Picture p)
But in this approach, my p.keywords property is always empty. Is there some way to help the framework recreate my p.keywords property before it hits my controller's action method?
I thought an Editor Template might work here, but I don't think there is a way to model bind a nested IEnumerable view model member. Your fastest bet may be handling it directly with FormCollection and some string parsing magic. Otherwise, if you have to strongly-type this, maybe a custom model binder like this could help if you can control your keyword element id's:
public class PictureKeywordBinder : IModelBinder
{
public object GetValue(ControllerContext controllerContext,
string modelName, Type modelType,
ModelStateDictionary modelState)
{
Picture picture = new Picture();
//set name, url, other paramaters here
foreach(var item in Request.Form.Keys)
{
if (item.StartsWith("keyword"))
{
picture.keywords.Add(Request.Form[item]);
}
}
//add any errors to model here
return picture;
}
}
Maybe the keyword id's could be setup in a partial view passed the sub model from your parent view:
<% Html.RenderPartial("PictureKeywords", Model.keywords);
Are your keywords seperate text boxes? If so, create an inputs like this and they will be populated by the model binder.
<input name="keywords[0]" type="text">
<input name="keywords[1]" type="text">
<input name="keywords[2]" type="text">
The way I got around this, is to use a hidden input to store the csv string of items, in your case, keywords.
I then hooked into the form submit event (using jQuery) and appended the inputs to form the csv string, which is then stored in the hidden input. This hidden input was strongly typed to a property on my model.
It's a little clunky, but if you have a dynamic number of possible keywords then this works quite well (except if JS is disabled of course)
In what way you are expecting the user to add more keywords? In the form comma separated values(CSV) or by dynamically adding textboxes?
Based on your requirement, i have two solutions with me.

MVC Controller parameter for a form element with a dot in it?

If you're using the Html.TextBoxFor() type methods, you may well end up with Form controls that have dots in their names, like this:
<input type="text" name="Contact.FirstName" id="Contact_FirstName" />
If you want MVC to map those named fields to parameters in your controller (as opposed to an object parameter or whatever), you have to get the parameter names right. What to do about the dots?
Neither this:
[HttpPost]
public ActionResult FooAction(string firstName)
not this:
[HttpPost]
public ActionResult FooAction(string contact_FirstName)
seem to work.
Edit: Having a suitable object parameter would work (eg see clicktricity's answer), but I'm looking for a way to do it with named value parameters.
I have found another way, a kind of hack because I believe this is misuse of BindAttribute, to associate firstName parameter with Contact.FirstName input element:
[HttpPost]
public ActionResult FooAction([Bind(Prefix="Contact.FirstName")]string firstName)
This for sure works with ASP.NET MVC 1.
Depending on the other form controls, you should be able to have the MVC default model binder construct a Contact object for you. Then the signature of your action method would be:
[HttpPost]
public ActionResult FooAction(Contact contact)
Then the Contact.FirstName (and any other fileds) will be bound correctly
As Clicktricity suggests in comments you may use
[HttpPost]
public ActionResult FooAction(FormCollection form)
{
firstName = form["Contact.FirstName"];
}

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