asp.net mvc formcollection - asp.net-mvc

public ActionResult Edit(int id, FormCollection formValues) {
// Retrieve existing dinner
Dinner dinner = dinnerRepository.GetDinner(id);
// Update dinner with form posted values
dinner.Title = Request.Form["Title"];
dinner.Description = Request.Form["Description"];
dinner.EventDate = DateTime.Parse(Request.Form["EventDate"]);
dinner.Address = Request.Form["Address"];
dinner.Country = Request.Form["Country"];
dinner.ContactPhone = Request.Form["ContactPhone"];
// Persist changes back to database
dinnerRepository.Save();
// Perform HTTP redirect to details page for the saved Dinner
return RedirectToAction("Details", new { id = dinner.DinnerID });
}
formValues is not used in the method. What is its purpose?

One of the major advancements of MVC is getting rid of this left - right boring assignment code. It has mechanisms in place that can do this work for you. In this case, you could do something like this:
Dinner dinner = dinnerRepository.GetDinner(id);
UpdateModel(dinner, formValues); // Automatically updates properties with values from the collection
dinnerRepository.Save();
Hope this helps.

Just to make a few comments,
dinner.EventDate = DateTime.Parse(Request.Form["EventDate"]); is what model binding is supposed to get rid of.
Using a strongly typed view, you should get a DateTime type back into dinner.EventDate, without having to do that assigning yourself.
The FormCollection returns all the inputs that were submitted via the html form and you are able to retrieve those elements by using the following syntax
formCollection["Title"] given that the input element's name is "Title"
Strongly typed views are just amazing!

Look at how FormCollection is used here: How can a formcollection be enumerated in ASP.NET MVC?

Related

Update entity with ViewModel and Entity Framework 6?

I've been looking around and can't quite find the answer. I'm using a ViewModel in my Edit View so that I can have values for some dropdownlist. Now when I go to update my DB I'm not understanding how I can update my database record. I'm guessing I could create a new entity object, do a Find, and then update each property based on the ViewModel passed in from the Form but that sure seems like a lot of manual work.
Here I'm using the VeiwModel in the Edit View.
#model CPPCustomerCall.ViewModels.CustomerCallVM
Here is my controller's ActionResult. I changed the object type of the ActionResult to take in CustomerCallVM instead of the CustomerCall which was auto-generated. I assume since the Edit View's model is the ViewModel that's the type of object the ActionResult will receive. However, my ViewModel has more properties that aren't needed for the Entity Model to update the record. How do I go about updating my DB record in this ActionResult?
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<ActionResult> Edit([Bind(Include = "Id,CustomerName,Subject,PhoneNumber,CallMessage,CallDate,Status,CallNotes")] CustomerCallVM customerCall)
{
if (ModelState.IsValid)
{
db.Entry(customerCall).State = EntityState.Modified;
await db.SaveChangesAsync();
return RedirectToAction("Index");
}
return View(customerCall);
}
First, Bind and view models are mutually exclusive. If you don't want something to be eligible to be modified, then it shouldn't be on your view model, in the first place. Barring that, view models diverge from entities in the sense that they can't be saved directly. As a result, there's always some intervention present on your part to map the posted values back onto the entity, which means you can then selectively not map over certain properties that shouldn't be, regardless of whether they were posted or not. Long and short, get rid of the Bind stuff. It's just something else to maintain and a huge source of potential bugs.
That said, the code you have is workable; you're just missing the crucial part where you map the data from your view model back onto your entity. First, you need to fetch the entity from the database so you have a base to work from:
var customerCall = db.CustomerCalls.Find(id);
if (customerCall == null)
{
return new HttpNotFoundResult();
}
FWIW, your edit route should include the id in the route, according to REST conventions. Following REST isn't strictly required, but it's certainly recommended. While a web application adhering to REST doesn't mean it's a good application, not adhering to rest is generally a sure sign of a badly designed and coded application.
Then, you map over your properties. You can either do this manually:
customerCall.CustomerName = model.CustomerName;
// etc.
Or you can use a library like AutoMapper.
mapper.Map(model, customerCall);
AutoMapper requires a bit of initial setup to make this magic work, of course, so review the docs, if you're going that route. Manual mapping is easier, but far more tedious and repetitive.
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<ActionResult> Edit([Bind(Include = "Id,CustomerName,Subject,PhoneNumber,CallMessage,CallDate,Status,CallNotes")] CustomerCallVM customerCall)
{
if (ModelState.IsValid)
{
// Find The record you need
var dbObj = CustomerCalls.FirstOrDefault(x=> x.id = customerCall.id);
//Check if null
if(dbObj == null) dbObj = new CustomerCall();
/// Map your properties
// Add object to the stack
if(dbObj.id == 0){
CustomerCalls.Add(dbObj);
}else{
CustomerCalls.Update(dbObj);
}
await db.SaveChangesAsync();
return RedirectToAction("Index");
}
return View(customerCall);
}

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

What is FormCollection argument for? Is it a dummy argument?

Up to now I have no idea why does VS provide FormCollection argument by default?
public ActionResult Edit(int id)
{
Dinner dinner = dinnerRepository.GetDinnerById(id);
if (dinner == null)
return View("NotFound");
else
return View(dinner);
}
[HttpPost]
public ActionResult Edit(int id, object dummy/*, FormCollection collection*/)
{
Dinner temp = dinnerRepository.GetDinnerById(id);
if (TryUpdateModel(temp))
{
dinnerRepository.Save();
return RedirectToAction("Details", new { id = temp.DinnerId });
}
else
return View(temp);
}
EDIT 1: In my experiment, any arguments other than id are dummy because they never be used in httppost Edit action method.
EDIT 2: Does TryUpdateModel use FormCollection behind the scene?
If your app receives a POST, then 99.99% of the time it will come from an HTML form. The FormsCollection gathers all the values in the form for you.
In ASP.NET MVC you are almost always better off using strongly typed objects though. The DefaultModelBinder will create them for you most of the time, and you can implement IModelBinder if needed if the default one doesn't do what you need.
The FormCollection is how ASP.NET provides you access to the values that were just posted to your page.
You could also use a strongly typed argument and then ASP.NET MVC would use the FormCollection internally to create your strongly typed object.
FormCollection contains your form state coming back to your server.
If you need any custom operation on the processing of your data you use FormCollection. Otherwise you can happily remove it.
I am using it heavily for a hierarchical model processing.

Example of an ASP.NET MVC post model?

I was watching the HaHaa presentation on ASP.NET MVC from MIX and they mentioned using a Post Model where I guess they were saying you could use a model that was ONLY for posting. I have tried looking for examples for this. Am I not understanding what they are saying? Does anyone have an example of how this might work in a strongly typed view where the view model and post model are not of the same type?
Below is ScottGu's example expanded a bit. As #SLaks explained, when the POST is received, MVC will try to create a new MyPostName object and match its properties with the from fields. It will also update the ModelState property with the results of the matching and validation.
When the action returns the view, it has to provide a model for it as well. However, the view doesn't have to use that same model. In fact, the view can be strongly typed with a different model, that contains the expanded data, for example it can have navigation properties bound to external keys in the DB table; and if that's the case, the logic to map from the POST model to the view model will be contained in the POST action.
public class MyGetModel
{
string FullName;
List<MyGetModel> SuggestedFriends;
}
public class MyPostModel
{
string FirstName;
string LastName;
}
//GET: /Customer/Create
public ActionResult Create()
{
MyGetModel myName = new MyGetModel();
myName.FullName = "John Doe"; // Or fetch it from the DB
myName.SuggestedFriends = new List<MyGetModel>; // For example - from people select name where name != myName.FullName
Model = myName;
return View();
}
//POST: /Customer/Create
[HttpPost]
public ActionResult Create(MyPostModel newName)
{
MyGetModel name = new MyGetModel();
name.FullName = newName.FirstName + "" + newName.LastName; // Or validate and update the DB
return View("Create", name);
}
The POST model would only be used to pass the data into your action method.
The model that the POST action sends to its view doesn't need to be related to the model that it received (and usually will not be).
Similarly, the model that the initial GET action (that shows the form in the first place) passes to its view (which submits to the POST action) doesn't need to be related to the model that the POST action takes (although it usually will be the same model)
As long as it has properties that match your input parameters, you can use any model you want for the parameter to the POST action.

How does the ASP.NET MVC UpdateModel() method work?

I'm working on my first .NET MVC application and using the NerdDinner tutorial as a reference point. One point that is intriguing me at the moment is the UpdateModel() method. (I don't like using things I don't really understand.)
Taken from the NerdDinner tutorial -
//
// POST: /Dinners/Edit/2
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(int id, FormCollection formValues) {
Dinner dinner = dinnerRepository.GetDinner(id);
UpdateModel(dinner);
dinnerRepository.Save();
return RedirectToAction("Details", new { id = dinner.DinnerID });
}
My main question is how does the UpdateModel() get access to the formValues passed in the Edit method? Why is the collection not passed in explicitly as a parameter to the method?
UpdateModel() is a Controller helper method that attempts to bind a bunch of different input data sources (HTTP POST data coming from a View, QueryString values, Session variables/Cookies, etc.) to the explicit model object you indicate as a parameter. Essentially, it is only for model binding.
If you express the input parameters for your Action as a strongly-typed model (like a View Model), you've already taken all of the steps that are done behind the scenes when UpdateModel() is called. If you retrieve an object from the DataContext and edit its properties, SaveChanges() is all you need to push the updates back to the database (in this case, Save()).
Example:
//
// POST: /Dinners/Edit/2
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(DinnerViewModel incoming) {
var dinner = dinnerRepository.GetDinner(incoming.DinnerID);
dinner.Description = incoming.Description;
dinnerRepository.Save();
return RedirectToAction("Details", new { id = incoming.DinnerID });
}
However, there is a use-case for using UpdateModel() with a strongly-typed model: when you are passing in a strongly-typed model and want its values to directly replace those of an entity from the database (provided they are all named and typed the same). In this case, you would retrieve the object, use UpdateModel() on it, and its model binding operation will pull in any similarly-named and typed properties from the strongly-typed object to the retrieved object. In other words, it will perform reflection for you.
So, like your example, if you want all properties to update without specifying which to update, and your strongly-typed model and database model have similarly-named properties, you would still want to use UpdateModel() to take advantage of the reflection.
Example:
//
// POST: /Dinners/Edit/2
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(DinnerViewModel incoming) {
var dinner = dinnerRepository.GetDinner(incoming.DinnerID);
UpdateModel(dinner);
dinnerRepository.Save();
return RedirectToAction("Details", new { id = incoming.DinnerID });
}
The only advantage here (over using a FormCollection object) is that you'd have access to all other properties of the strongly-typed object (as shown by incoming.DinnerID).
Conclusion: if you're translating a strongly-typed object to a derived object, it's probably easiest to use UpdateModel(). However, it's largely unnecessary if you are simply updating a few properties of the derived object. Also, be aware that use of the Entity Framework (instead of something like Linq to SQL) makes all of this moot, as it can relate strongly-typed objects and derived objects with its own methods.
It does inspect all the HttpRequest inputs such as Form, QueryString, Cookies and Server variables. I think in this order.
Instead of passing Model object as a parameter to "Post()" action method, we are creating an instance of an Model object within the "Post()" function, and updating it using "UpdateModel()" function. "UpdateModel()" function inspects all the HttpRequest inputs such as posted Form data, QueryString, Cookies and Server variables and populate the employee object.
e.g.
[HttpPost]
[ActionName("Create")]
public ActionResult Create_Post()
{
EmployeeBusinessLayer employeeBusinessLayer =
new EmployeeBusinessLayer();
Employee employee = new Employee();
UpdateModel(employee);
employeeBusinessLayer.AddEmmployee(employee);
return RedirectToAction("Index");
}

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