Assume we have update form.
This form requires two actions. One of them for GET request to show data and second for POST request to save changes.
[HttpGet]
public ActionResult Update(int id)
{
var viewModel = GetViewModel(id);
viewModel.Dictionaries = GetUpdateDictionaries(id);
return View(viewModel);
}
[HttpPost]
public ActionResult Update(UpdateViewModel viewModel)
{
if(Model.IsValid)
{
Save(viewModel);
return RedirectToHome();
}
viewModel.Dictionaries = GetUpdateDictionaries(id);
return View(viewModel);
}
It is a classical approach. We pass to POST update the same view model. But with this view model we pass many unnecessary data. For example dictionaries. Someone tells that it is a bad practice and suggest two alternative ways:
1) Use view model only for form data and pass dictionaries and other stuuf through ViewBug
2) Create special class only for necessary form data and use it in post update action.
Are there standart approach?
If your dictionaries are not part of the Model then the alternatives which MVC provide for passing information to the View is:
ViewData["MyDictionaries"]= GetUpdateDictionaries(id);
or
TempData["MyDictionaries"]= GetUpdateDictionaries(id);
or for .Net 4:
ViewBag.MyDictionaries= GetUpdateDictionaries(id);
Is your concern that viewModel.Dictionaries will all get sent to the client browser and then get posted back to the server? It won't. Only things that you render in markup e.g. with Html.TextBoxFor() get sent to the browser. So your current code is okay from that point of view.
The real objection to your dictionaries is, if the dictionaries are not a part of the thing your Model is a model of. The point of OO is that your models are models of something; so should only have properties corresponding to the something that it models.
If your models are not models of something, but only ViewModels, then putting the dictionaries on them in fine. But in that case, Save(model) would not be fine.
Related
If I have a model that looks something like this:
public class LoginModel
{
pulbic List<string> UserNames {get; set; }
public string SelectedUserName {get; set; }
public string Password {get; set; }
}
And I also have a controller with a couple of action methods that look something like this:
public ActionResult Login()
{
LoginModel model = null;
model = new LoginModel();
// Code to populate the UserNames property of the LoginModel instance (model)...
return View(model);
}
[HttpPost()]
public ActionResult Login(LoginModel model)
{
if (ModelState.IsValid == true)
{
return RedirectToAction("SomeOtherAction")
}
else
{
return View(model);
}
}
I will need to re-populate the UserNames property of the model object before passing it to the View method. This is something that I can certainly do but it does feel a bit dirty. That leads me to the question. Is there a better way to handle this?
This is something that I can certainly do but it does feel a bit dirty.
It's not dirty. It's how MVC works -> it's stateless. As an alternative you could include the list of usernames as hidden fields into the form so that they get POSTed back to the controller. But this is not an information you could rely upon because the user could modify those values. So if you need to trust those values you'd better query your backend for them.
As I have come to understand MVC are that you should have a method in the model update the UserNames property. All (and nothing more in this matter) your controller should do is to pass the necessary arguments to this function. In that way, your controller is just passing the information which only it can know to the model where the logic should go.
I don't know any asp.net so I can sadly not provide you with a code example.
Essentially this depends on what your view is actually doing. Certainly if you render your UserNames collection as a list of hidden form fields Model binding could do this for you upon http post. That said this is how http programming is intended to work. State is not intended to stick around between gets and posts.
Really your choices are to rebuild that list on as you mentioned or render out some hidden fields (I would not recommend that) and have model binding do its thing.
Usually I have a class for a particular model(and closely related entities) that handles database access and populating view models(although you can add even another layer in so that DB access and mapping to view models is separate, perhaps leveraging a mapping framework). Either way, it would have a method like GetLogins that you could call anywhere that needs a list like that, perhaps even other controllers like Friends page that needs to list login names that someone can request friends from, a contrived example but you get the idea.
Since both your Get and POST methods need to re-display the page(POST in the case of an error), both of them can call GetLogins so that you don't repeat that DB access code in both places.
I am new to MVC and am having a conceptual problem with state and object persistence and hope someone can put my thoughts in order.
I have a remote webservice which provides methods to manage orders. An order consists of a header and Lines as you would expect. Lines can have additional requirements.
I have my domain objects created (using xsd2code from the webservice schema), the webservice calls and object serialization all working fine. I've build the DAL/BLL layers and it's all working - tested using a WinForms testbed app front-end.
I have view model objects mapped from the domain objects using Automapper. As the order is returned from a single webservice method complete with lines etc I have an OrderViewModel as follows
public class OrderViewModel
{
public OrderHeaderViewModel OrderHeader { set; get; }
public List<OrderLineViewModel> OrderLines { set; get; }
public List<OrderLineAdditionalViewModel> OrderLineAdditional { set; get; }
public List<OrderJustificationViewModel> OrderJustifications { set; get; }
}
Firstly I'm wondering if I should dispense with the OrderViewModel as if I pass this as a model to a view I'm passing far more data than I need. Views only need OrderHeader or OrderLines etc - not the entire order.
Now my conceptual problem is in the controllers and the views and object persistence.
My Order controller has a Detail Action which performs the load of the order from the webservice and maps the Domain object to the OrderViewModel object.
public ActionResult Details(string orderNumber)
{
OrderViewModel viewModel = new OrderViewModel();
var order = WebServiceAccess.LoadOrderByOrderNumber(orderNumber,"OBOS_WS");
viewModel = AutoMapper.Mapper.Map<BusinessEntities.Order, ViewModels.OrderViewModel>(order);
return View(viewModel);
}
But the Order/Details.cshtml just has the page layout and a call to two partial pages for the header and the lines (I swap the Headerview for a HeaderEdit using Ajax, same for the LinesView)
#{ Html.RenderPartial("DetailsHeaderViewPartial", Model);}
#{ Html.RenderPartial("DetailsLinesViewPartial", Model);}
At the moment I'm passing the model into the main Details container page, then into the RenderPartials, However I don't think that the model should be passed to the main Detail page, as it doesn't need it - the model is only needed in the DetailsHeaderViewPartial, DetailsLinesViewPartial so I'd be better off using #RenderAction here instead and passing the model into the Header/Lines views instead.
However, The Order is retrieved from the webservice in the ActionResult Details() how can I make the retrieved OrderViewModel object available in the ActionResult HeaderDetails() / LineDetails() methods of the controller to pass as the model in return PartialView(...,model) ?
Should I use a User Session to store the Order ViewModel so it can be used across actions in the controller.
Moving on from this stage the user will be able to maintain the order (add/remove lines - edit the header etc). As the webservice call to save the order could take a few seconds to complete I'd rather only call the save method when the user has finished with the order. I therefore would like to persist the in-progress order locally somewhere whilst it's being worked on. User session ?
Many thanks for any advice. Once I've got my head around state management for the ViewModels I'll be able to stop reading a million Blog posts and actually write this thing !
You actually have a few questions here so I will try to address them all the best I can.
1) Dispensing with the view model : I would say no. The view model represents the data that you need in order to populate your view. It seems like you are using the view model as an identical container to the domain model object. So you are asking if you should dispense with it and just pass the domain model to the view while your original concern is that you are passing along more data then you really need as is?
Rather then dispensing with the view model, I would revisit your properties on your view model. Only use properties that you need and create the mapping logic (either with automapper or on your own) for taking the complex domain object and populating the properties on the view model.
summation: build the view model to be only things that the view needs and write mapping logic to populate that view model.
2) This is just a statement of best practice before I breakdown your specific scenario.
You describe your architecture as having a BLL and DAL. If that is the case then you should not be persisting any objects from your controller. The controller should not have any knowledge of the database even existing and the objects used in the controller should have no idea of how to persist themselves. The objects that are going between your controller and the web service should strictly be Data Transfer Objects (DTO's). If you are unfamiliar with what constitutes a DTO then I highly suggest that you do some research and try to build them into your solution. It will help you conceptually see the difference between view model objects, domain objects and data transfer objects.
3) I would not try to store an order object in the session. I would re-analyze how you are breaking up the partial views within the view so that you can call actions with the ordersviewmodel being the parameter in a way that you need. It sounds like you are needlessly breaking up views into partial views.
4) You should not be concerned with state management for the view model object. Your view (which can be comprised of many partial views) is filled based on properties provided by the view model. The user can make changes using the UI you have developed. Since you express the desire to only save once they are finished making all changes to optimize calls to the web service, you just need to repopulate the fields of the view model upon clicking submit. Now you have a "state" for orderviewmodel that represents the users changes. You can send this object to the web service after converting back to a DTO (if you do what I said above) or by mapping it to the domain object.
1 final note. You are using automapper to map your domain to the view model. I am assuming that your view model is too complex and includes things that you don't need because you built your view model to emulate the domain object so that automapper could map by naming convention. Automapper has an api for doing complex (custom) mappings that fall outside of standard same name properties. Don't let automapper constrain you to building your view models a certain way.
Hope this helps
I have An EntityModel that is named ECommerceEntities that contains several entities. If I want to use this model in a view in asp.net mvc, Can I pass ECommerceEntities instance to view or Sould I pass one entity in ECommerceEntities.
I mean :
//Can I use this?
public ActionResult Index()
{
ECommerceEntities entity = new ECommerceEntities();
return View(entity);
}
or
//Should I use this?
public ActionResult Index()
{
ECommerceEntities.OneEntity one_entity = new ECommerceEntities.OneEntity();
//filling one_entity here and then send to view
return View(one_entity );
}
Thanks.
If you are asking if it is possible, it is possible to do both. Yes, both options will work. However if you only need the sub entity in the view, I would just pass the sub entity into the view. No use in passing in more than needed right?
Do not forget that in MVC whatever object you pass in to your view,(EcommerceEntities for example) can have its properties set in the post by MVC's automatic model binding which maps data from the post into the object you pass into the view.
So, this means that someone can hijack the http post and can fill in EcommerceEntities and its sub entities with various bits of random data of their choosing if you are not careful and you may accidentally save this data to your db because you did not expect some of these properties to get set.
So, when working in MVC you have to protect properties that are not being used in your view but are passed into the view to ensure that nobody has injected them.
If you do decide to pass in EcommerceEntities, make sure that you use whitelisting or look at MVC's bind attribute to protect your data when your entity is posted back to your controller.
Because of the work involved in protecting that much extra data, I would say that the sub entity would be best if the screen will populate correctly just off of the sub entity object.
Hopefully this is helpful.
If you want to display a list of all entities (which the Index action is typically used for), you probably want to get all the entities from your database context:
public ActionResult Index()
{
// assumes dbContext is already initialized
ICollection<ECommerceEntities> entities = dbContext.ECommerceEntities
return View(entities);
}
I'm begginer in asp.net mvc and i have some doubts.
P.S: I'm using DDD to learn
I have an ACtion in a Controller and it'll save an entity (from my model) by a repository (for a database).
My doubts is, How can I get the informations from the View and save it by a repository in my Controller ?
Is it correct to get an entity of my Model in Save method of controller, like this:
public ActionResult Save(Product product)
{
// validate object
// save data in repository
return View("Success");
}
Or Need I get an DTO (with a structure similar to my entity) and create an object passing property by property to an entity ?
I didnt' like of FormCollection and I'd like to know, What is recommended architecturally ?
Thanks a lot guys
Cheers
I you want to follow DDD practices as described by the Blue Book you should bind your views to DTO's which can be forwarded to a thin 'Application' layer where Domain objects are created or retrieved from database. This application layer can be a simple facade with methods or can leverage command pattern.
For a live demo, you can see my project -- DDDSample.NET
This kind of problem can be fixed by adding so called view model.
Basically - a view model is DTO that provides data for particular view. In similar fashion - view models are used to get data back from view via model binding. Then - controller just forwards necessary data to domain model.
Typically, in ASP.NET MVC your controller actions will receive strongly typed objects returned by the DefaultModelBinder when editing entity types. Using this pattern you can pass a "Product" to your GET view either by itself or as part of a DTO and then your "Save" method would receive a "Product" object in its parameter list.
So long as you are using either editor templates or fields with matching names (i.e. Html.TextBox("Name") corresponds to Product.Name) then the DefaultModelBinder should be able to correctly fill the typed entity object passed to the action method. You shouldn't have to mess with the FormCollection except in certain edge cases.
[HttpGet]
public ActionResult Create() {
return View("Create", new Product());
}
[HttpPost]
public ActionResult Create(Product product) { //or Save(Product)
...
}
As long as your form has fields which match the fields in Product, they should automatically be populated for you based on the values. How you save the entity depends on the data model, whether you're creating a new record or editing an existing one, etc.
I want to be able to send JSON as opposed to the standard QueryStrings when making a post to my controllers in ASP.Net MVC. I have the Front-End stuff working fine (building and then submitting my JSON objects).
The problem is on the controller side where the default ModelBinders that ship with the MVC framework do not support this.
I have seen a combination of ways around this, one of them is to apply a filter which takes the object as a parameter, uses a JSON library to de-serialise it, and adds that to the action parameters. This is not ideal.
The other, better, way is to use a custom Model Binder. All the ones I have seen though presume you will have only one model and that will be a class rather than a variable. If you have multiple ones it breaks down.
Has anyone else encountered this? One idea I had was if I could simply override how MVC deals with the FormCollection and intercept there, adding the values to the collection myself and hoping MVC can do the rest in it's normal fashion. Does anyone know if that is possible?
The key issue, I think, is that my problem is not with binding because my view models are no different to how they where before. The problem is getting the values from the JSON Post.
If I am correct MVC get's the values from the QueryString and puts it into the form collection which is then used for ModelBinding. So shouldn't the correct method be to change the way the FormCollection gets assigned?
Example of an action:
public ActionResult MyFirstAction(Int32 ID, PersonObject Person, ClassObject ClassDetails)
{
//etc
}
The normal binding works, JSON doesn't and all the example of Model Binders will not work either. My best solution so far is to convert the object to a dictionary and loop though each param and match it up. Doesn't seem ideal.
I use a custom model binder for json like this:
public class JsonModelBinder<T> : IModelBinder {
private string key;
public JsonModelBinder(string requestKey) {
this.key = requestKey;
}
public object BindModel(ControllerContext controllerContext, ...) {
var json = controllerContext.HttpContext.Request[key];
return new JsonSerializer().Deserialize<T>(json);
}
}
And then wire it up in Global.asax.cs like this:
ModelBinders.Binders.Add(
typeof(Product),
new JsonModelBinder<Product>("ProductJson"));
You can read more about this here: Inheritance is Evil: The Epic Fail of the DataAnnotationsModelBinder
EDIT
The JsonModelBinder should be used on the controller action parameter typed as Product only. The Int32 and ClassObject should fall back to the DefaultModelBinder. Are you experiencing a different result?