I am new in Asp.net MVC 4
I write function using MVC controller
public ActionResultRole_name(string role)
{
return role;
}
My question is how to display return value on cshtml razor view?
You could return a ViewResult:
public ActionResult Role_name(string role)
{
return View((object)role);
}
and in the corresponding Role_name.cshtml view you could use this value:
#model string
<div>The role is #Model</div>
Notice how it was necessary to cast the role variable to an object to ensure that the proper View method overload (taking a model) is being resolved.
On the other hand you could have used a view model which is always best practice:
public class MyViewModel
{
public string Role { get; set; }
}
which your controller action could have populated and passed to the corresponding stringly typed view:
public ActionResult Role_name(string role)
{
var model = new MyViewModel();
model.Role = role;
return View(model);
}
and in the view:
#model MyViewModel
<div>The role is #Model.Role</div>
Also I would recommend you taking a look at some of the getting started tutorials on the asp.net/mvc site.
Related
I have a ViewModel that has a complex object as one of its members. The complex object has 4 properties (all strings). I'm trying to create a re-usable partial view where I can pass in the complex object and have it generate the html with html helpers for its properties. That's all working great. However, when I submit the form, the model binder isn't mapping the values back to the ViewModel's member so I don't get anything back on the server side. How can I read the values a user types into the html helpers for the complex object.
ViewModel
public class MyViewModel
{
public string SomeProperty { get; set; }
public MyComplexModel ComplexModel { get; set; }
}
MyComplexModel
public class MyComplexModel
{
public int id { get; set; }
public string Name { get; set; }
public string Address { get; set; }
....
}
Controller
public class MyController : Controller
{
public ActionResult Index()
{
MyViewModel model = new MyViewModel();
model.ComplexModel = new MyComplexModel();
model.ComplexModel.id = 15;
return View(model);
}
[HttpPost]
public ActionResult Index(MyViewModel model)
{
// model here never has my nested model populated in the partial view
return View(model);
}
}
View
#using(Html.BeginForm("Index", "MyController", FormMethod.Post))
{
....
#Html.Partial("MyPartialView", Model.ComplexModel)
}
Partial View
#model my.path.to.namespace.MyComplexModel
#Html.TextBoxFor(m => m.Name)
...
how can I bind this data on form submission so that the parent model contains the data entered on the web form from the partial view?
thanks
EDIT: I've figured out that I need to prepend "ComplexModel." to all of my control's names in the partial view (textboxes) so that it maps to the nested object, but I can't pass the ViewModel type to the partial view to get that extra layer because it needs to be generic to accept several ViewModel types. I could just rewrite the name attribute with javascript, but that seems overly ghetto to me. How else can I do this?
EDIT 2: I can statically set the name attribute with new { Name="ComplexModel.Name" } so I think I'm in business unless someone has a better method?
You can pass the prefix to the partial using
#Html.Partial("MyPartialView", Model.ComplexModel,
new ViewDataDictionary { TemplateInfo = new TemplateInfo { HtmlFieldPrefix = "ComplexModel" }})
which will perpend the prefix to you controls name attribute so that <input name="Name" ../> will become <input name="ComplexModel.Name" ../> and correctly bind to typeof MyViewModel on post back
Edit
To make it a little easier, you can encapsulate this in a html helper
public static MvcHtmlString PartialFor<TModel, TProperty>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TProperty>> expression, string partialViewName)
{
string name = ExpressionHelper.GetExpressionText(expression);
object model = ModelMetadata.FromLambdaExpression(expression, helper.ViewData).Model;
var viewData = new ViewDataDictionary(helper.ViewData)
{
TemplateInfo = new System.Web.Mvc.TemplateInfo
{
HtmlFieldPrefix = string.IsNullOrEmpty(helper.ViewData.TemplateInfo.HtmlFieldPrefix) ?
name : $"{helper.ViewData.TemplateInfo.HtmlFieldPrefix}.{name}"
}
};
return helper.Partial(partialViewName, model, viewData);
}
and use it as
#Html.PartialFor(m => m.ComplexModel, "MyPartialView")
If you use tag helpers, the partial tag helper accepts a for attribute, which does what you expect.
<partial name="MyPartialView" for="ComplexModel" />
Using the for attribute, rather than the typical model attribute, will cause all of the form fields within the partial to be named with the ComplexModel. prefix.
You can try passing the ViewModel to the partial.
#model my.path.to.namespace.MyViewModel
#Html.TextBoxFor(m => m.ComplexModel.Name)
Edit
You can create a base model and push the complex model in there and pass the based model to the partial.
public class MyViewModel :BaseModel
{
public string SomeProperty { get; set; }
}
public class MyViewModel2 :BaseModel
{
public string SomeProperty2 { get; set; }
}
public class BaseModel
{
public MyComplexModel ComplexModel { get; set; }
}
public class MyComplexModel
{
public int id { get; set; }
public string Name { get; set; }
...
}
Then your partial will be like below :
#model my.path.to.namespace.BaseModel
#Html.TextBoxFor(m => m.ComplexModel.Name)
If this is not an acceptable solution, you may have to think in terms of overriding the model binder. You can read about that here.
I came across the same situation and with the help of such informative posts changed my partial code to have prefix on generated in input elements generated by partial view
I have used Html.partial helper giving partialview name and object of ModelType and an instance of ViewDataDictionary object with Html Field Prefix to constructor of Html.partial.
This results in GET request of "xyz url" of "Main view" and rendering partial view inside it with input elements generated with prefix e.g. earlier Name="Title" now becomes Name="MySubType.Title" in respective HTML element and same for rest of the form input elements.
The problem occurred when POST request is made to "xyz url", expecting the Form which is filled in gets saved in to my database. But the MVC Modelbinder didn't bind my POSTed model data with form values filled in and also ModelState is also lost. The model in viewdata was also coming to null.
Finally I tried to update model data in Posted form using TryUppdateModel method which takes model instance and html prefix which was passed earlier to partial view,and can see now model is bound with values and model state is also present.
Please let me know if this approach is fine or bit diversified!
I am new to MVC and I have got a list of students in my action method and i want to pass each student instance to a view inside a foreach loop something like that
foreach(var student in Students)
{
return View(student);
// instead of return i have also tried this View(student) but it also doesnt work
}
Is it possible?
Actually i dont want to pass complete list to view instead of it I want to pass each student instance to a view by [httpget]and after getting its updated information like marks and grades in [httppost] i would like to send next student to view and get its updated information. It would be much easier for user to enter details of one student at a time instead of dealing with a complete list
You can pass it as object to method
// from your controller
List<yourobject> list = new List<yourobject>();
return View(list);
// in your view
#model List<yourobject>
// and property Model is type of List<yourobject>
#foreach(var item in Model)
{
<span>#item.Name</span>//example
}
Also you can use the dynamic object ViewBag to pass data from Controllers to Views.
example :
ViewBag.MyStudentList = myStudentList;
#ViewBag.MyList
// e.g.
#foreach (var item in ViewBag.MyStudentList ) {
//you get data here
}
Else:
Declare a list in model class , and assign the student details to it , and include that model in view and access it
public class yourviewmodelStudent
{
public SubjectGradesViewModel()
{
Subjects = new List<Student>();
}
public List<Student> Studentdetails { get; set; }
}
//class that represnt your Student model
public class Student
{
public int Classnumber { get; set; }
public string Name { get; set; }
public List<Student> Studentdetails { get; set; }
}
//then in controller
var model = new yourviewmodelStudent();
model.Studentdetails =//assign your list
then
return View(model);
In view you get this list simply:
Obviously there are a number of ways to do this, but I thought I'd ask for a little feedback on benefits and drawbacks of the approaches.
First of all, the NerdDinner tutorial's Edit Action is in the form (say Form A):
[HttpPost]
public ActionResult Edit(int id, FormCollection collection) {
It seems to me that if you shape your ViewModels well to match your views, that the approach Form B:
[HttpPost]
public ActionResult Edit(MyViewModel mvm) {
just seems like a better, cleaner approach. I then just map the VM properties to the Model properties and save. However, if this ViewModel has other entities embedded in it that are initialized via the constructor (for example in the nerddinner tutorial), then this edit action fails if there is no default constructor and you'd have to use the first approach.
So, the first question is do you agree that generally Form B is usually better? Are there drawbacks?
Secondly, it seems then if Form B is used, the decorator type validation would need to be in the ViewModel. Are there advantages of embedding entities in ViewModels and keeping the validation at the entity level only?
This is a pretty general SO question.
the first question is do you agree that generally Form B is usually better?
The only time I do not use Form B is when I upload files. Otherwise, I don't believe anyone should ever need to use Form A. The reason I think people use Form A is a lack of understanding of the abilities of ASP.Net's version of MVC.
Secondly, it seems then if Form B is used, the decorator type validation would need to be in the ViewModel.
Sort of / it Depends. I'll give you an example:
public IValidateUserName
{
[Required]
string UserName { get; set; }
}
public UserModel
{
string UserName { get; set; }
}
[MetadataType(typeof(IValidateUserName))]
public UserValiationModel : UserModel
{
}
The validation decorator is in an interface. I'm using the MetadataType on a derived class to validate the derived type. I personally like this practice because it allows reusable validation and the MetadataType/Validation is NOT part of the ASP.NET core functionality, so it can be used outside of ASP.Net (MVC) application.
Are there advantages of embedding entities in ViewModels ..
Yes, I do my absolute best to never pass a basic model to the view. This is an example of what I don't do:
public class person { public Color FavoriteColor { get; set; } }
ActionResult Details()
{
Person model = new Person();
return this.View(model);
}
What happens when you want to pass more data to your view (for partials or layout data)? That information is not Person relevant most of the time so adding it to the Person model makes no sense. Instead, my models typically look like:
public class DetailsPersonViewModel()
{
public Person Person { get; set; }
}
public ActionResult Details()
{
DetailsPersonViewModel model = new DetailsPersonViewModel();
model.Person = new Person();
return this.View(model);
}
Now I can add required data the DetailsPersonViewModel that view needs beyond what a Person knows. For example, lets say this is going to display a for with all the colors for the Person to pick a favorite. All the possible colors aren't part of a person and shouldn't be part of the person Model, so I'd add them to the DetailPersonViewModel.
public class DetailsPersonViewModel()
{
public Person Person { get; set; }
public IEnumerable<Color> Colors { get; set; }
}
.. and keeping the validation at the entity level only?
System.ComponentModel.DataAnnotations weren't designed to validate properties' properties, so doing something like:
public class DetailsPersonViewModel()
{
[Required(property="FavoriteColor")]
public Person Person { get; set; }
}
Doesn't exist and doesn't make sense. Why ViewModel shouldn't contain the validation for the entity that needs validation.
this edit action fails if there is no default constructor and you'd have to use the first approach.
Correct, but why would a ViewModel or a Entity in a ViewModel not have a parameterless constructor? Sounds like a bad design and even if there is some requirement for this, it's easily solved by ModelBinding. Here's an example:
// Lets say that this person class requires
// a Guid for a constructor for some reason
public class Person
{
public Person(Guid id){ }
public FirstName { get; set; }
}
public class PersonEditViewModel
{
public Person Person { get; set; }
}
public ActionResult Edit()
{
PersonEditViewModel model = new PersonEditViewModel();
model.Person = new Person(guidFromSomeWhere);
return this.View(PersonEditViewModel);
}
//View
#Html.EditFor(m => m.Person.FirstName)
//Generated Html
<input type="Text" name="Person.FirstName" />
Now we have a form that a user can enter a new first name. How do we get back the values in this constructor? Simple, the ModelBinder does NOT care what model it is binding to, it just binds HTTP values to matching class properties.
[MetadataType(typeof(IPersonValidation))]
public class UpdatePerson
{
public FirstName { get; set; }
}
public class PersonUpdateViewModel
{
public UpdatePerson Person { get; set; }
}
[HttpPost]
public ActionResult Edit(PersonUpdateViewModel model)
{
// the model contains a .Person with a .FirstName of the input Text box
// the ModelBinder is simply populating the parameter with the values
// pass via Query, Forms, etc
// Validate Model
// AutoMap it or or whatever
// return a view
}
I have not yet taken a look at the NerDinner project, however, I generally try to avoid having a ViewModel in the POST of an action and instead, only have the elements of the "form" submitted.
For instance, if the ViewModel has a Dictionary that is used in some kind of dropdown, the entire dropdown will not be submitted, only the selected value.
My general approach is:
[HttpGet]
public ActionResult Edit(int id)
{
var form = _service.GetForm(id);
var pageViewModel = BuildViewModel(form);
return View(pageViewModel);
}
[HttpPost]
public ActionResult Edit(int id, MyCustomForm form)
{
var isSuccess = _service.ProcessForm(id);
if(isSuccess){
//redirect
}
//There was an error. Show the form again, but preserve the input values
var pageViewModel = BuildViewModel(form);
return View(pageViewModel);
}
private MyViewModel BuildViewModel(MyCustomForm form)
{
var viewModel = new MyViewModel();
viewModel.Form = form;
viewModel.StateList = _service.GetStateList();
return viewModel;
}
In the partial view I have to access Session variable LoginInfo which holds a LoginInfo object. I tried the following:
#LoginInfo info = #(LoginInfo)Session["LoginInfo"]
But it gives me compiler errors. What am I doing wrong?
What am I doing wrong?\
Many things. The first thing you did wrong is the Razor syntax. It should be:
#{ LoginInfo info = (LoginInfo)Session["LoginInfo"]; }
But that's just the syntax. You have a far bigger problem. You have a design problem. You are violating the MVC pattern.
A view should not try to fetch any data. A view uses data that is passed to it from the controller action under the form of a view model.
So you define a view model:
public class MyViewModel
{
public LoginInfo LoginInfo { get; set; }
}
then you have a controller action:
public ActionResult Foo()
{
var model = new MyViewModel();
model.LoginInfo = (LoginInfo)Session["LoginInfo"];
return View(model);
}
then you have a strongly typed view in which you use the view model:
#model MyViewModel
<div>Hello #Model.LoginInfo.FirstName</div>
But in this case (given the name of the class LoginInfo) I suppose that you are trying to display some common widget on all views. That would be a great candidate for using the Html.Action helper.
So you define controller action that will fetch this information from some data source (Session in your case):
[ChildActionOnly]
public ActionResult LoginInfo()
{
var model = (LoginInfo)Session["LoginInfo"] ?? new LoginInfo();
return PartialView(model);
}
and then you define a corresponding partial:
#model LoginInfo
<div>Hello #Model.FirstName #Model.LastName</div>
and finally in your _layout you can include this widget somewhere:
#Html.Action("LoginInfo", "SomeController")
There are a lot of articles devoted to working with data in MVC, and nothing about MVC 2.
So my question is: what is the proper way to handle POST-query and validate it.
Assume we have 2 actions. Both of them operates over the same entity, but each action has its own separated set of object properties that should be bound in automatic manner. For example:
Action "A" should bind only "Name" property of object, taken from POST-request
Action "B" should bind only "Date" property of object, taken from POST-request
As far as I understand - we cannot use Bind attribute in this case.
So - what are the best practices in MVC2 to handle POST-data and probably validate it?
UPD:
After Actions performed - additional logic will be applied to the objects so they become valid and ready to store in persistent layer. For action "A" - it will be setting up Date to current date.
I personally don't like using domain model classes as my view model. I find it causes problems with validation, formatting, and generally feels wrong. In fact, I'd not actually use a DateTime property on my view model at all (I'd format it as a string in my controller).
I would use two seperate view models, each with validation attributes, exposed as properties of your primary view model:
NOTE: I've left how to combining posted view-models with the main view model as an exercise for you, since there's several ways of approaching it
public class ActionAViewModel
{
[Required(ErrorMessage="Please enter your name")]
public string Name { get; set; }
}
public class ActionBViewModel
{
[Required(ErrorMessage="Please enter your date")]
// You could use a regex or custom attribute to do date validation,
// allowing you to have a custom error message for badly formatted
// dates
public string Date { get; set; }
}
public class PageViewModel
{
public ActionAViewModel ActionA { get; set; }
public ActionBViewModel ActionB { get; set; }
}
public class PageController
{
public ActionResult Index()
{
var viewModel = new PageViewModel
{
ActionA = new ActionAViewModel { Name = "Test" }
ActionB = new ActionBViewModel { Date = DateTime.Today.ToString(); }
};
return View(viewModel);
}
// The [Bind] prefix is there for when you use
// <%= Html.TextBoxFor(x => x.ActionA.Name) %>
public ActionResult ActionA(
[Bind(Prefix="ActionA")] ActionAViewModel viewModel)
{
if (ModelState.IsValid)
{
// Load model, update the Name, and commit the change
}
else
{
// Display Index with viewModel
// and default ActionBViewModel
}
}
public ActionResult ActionB(
[Bind(Prefix="ActionB")] ActionBViewModel viewModel)
{
if (ModelState.IsValid)
{
// Load model, update the Date, and commit the change
}
else
{
// Display Index with viewModel
// and default ActionAViewModel
}
}
}
One possible way to handle POST data and add validation, is with a custom model binder.
Here is a small sample of what i used recently to add custom validation to POST-form data :
public class Customer
{
public string Name { get; set; }
public DateTime Date { get; set; }
}
public class PageController : Controller
{
[HttpPost]
public ActionResult ActionA(Customer customer)
{
if(ModelState.IsValid) {
//do something with the customer
}
}
[HttpPost]
public ActionResult ActionB(Customer customer)
{
if(ModelState.IsValid) {
//do something with the customer
}
}
}
A CustomerModelBinder will be something like that:
public class CustomerModelBinder : DefaultModelBinder
{
protected override void BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, System.ComponentModel.PropertyDescriptor propertyDescriptor)
{
if (propertyDescriptor.Name == "Name") //or date or whatever else you want
{
//Access your Name property with valueprovider and do some magic before you bind it to the model.
//To add validation errors do (simple stuff)
if(string.IsNullOrEmpty(bindingContext.ValueProvider.GetValue("Name").AttemptedValue))
bindingContext.ModelState.AddModelError("Name", "Please enter a valid name");
//Any complex validation
}
else
{
//call the usual binder otherwise. I noticed that in this way you can use DataAnnotations as well.
base.BindProperty(controllerContext, bindingContext, propertyDescriptor);
}
}
and in the global.asax put
ModelBinders.Binders.Add(typeof(Customer), new CustomerModelBinder());
If you want not to bind Name property (just Date) when you call ActionB, then just make one more custom Model Binder and in the "if" statement, put to return the null, or the already existing value, or whatever you want. Then in the controller put:
[HttpPost]
public ActionResult([ModelBinder(typeof(CustomerAModelBinder))] Customer customer)
[HttpPost]
public ActionResult([ModelBinder(typeof(CustomerBModelBinder))] Customer customer)
Where customerAmodelbinder will bind only name and customerBmodelbinder will bind only date.
This is the easiest way i have found, to validate model binding, and i have achieved some very cool results with complex view models. I bet there is something out there that i have missed, and maybe a more expert can answer.
Hope i got your question right...:)