I'm developing something like wizard with steps (controllers) and uses DerivedModel1, DerivedModel2,etc which is inherits from BaseModel and extends them with extra properties.
Models - only data, without business logic. All logic performed by services in controllers action for example _step1Service.GetRelated(model.id).
Now I want to not just validate Model (for this case there is ValidationAttribute) but fix invalid data in BaseModel:
public class BaseModel
{
public DateTime StartDate {get;set;}
}
StartDate should be greater than today. User can select invalid date and instead of validation error application should fix this value (reset to default?).
In my first attempt I added service for validating/correcting StartDate and call in each Action:
public ActionResult Index(DerivedModel1 model)
{
_svc.fixModel(model);
if(!ModelState.IsValid)
{
return View();
}
... do stuff with valid data
}
But don't like that, because have to add this line to each controller and action.
Then I add this correction to StartDate setter. It's looks better, but this breaks popular MVC paradigm that all logic should be in controller (or maybe i misunderstood something?)
I was thinking about possible solutions of this problem: ActionFilterAttribute, custom ModelBinder? But not sure is this right way and whether it work.
What you think about that?
you must implement IModelBinder to achieve this.
first define your custom model binder like this:
public class MyCustomModelBinder : IModelBinder
{
public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
// Get the raw attempted value from the value provider
DateTime incomingDate = (DateTime) bindingContext.ValueProvider.GetValue("datefield").AttemptedValue;
//validate and correct date here ...
return new BaseModel{ DateMember = incomingDate };
}
}
then register your custom model binder such:
protected void Application_Start()
{
ModelBinders.Binders.Add(typeof (BaseModel), new MyCustomModelBinder());
}
and your controller :
public ActionResult YourAction([ModelBinder(typeof(MyCustomModelBinder )] BaseModel model)
{
return Content("Ok");
}
There's a difference between validation and business rules. Objects can (and often should) be responsible to make sure they are in a valid state themselves.
Related
My understanding is that ASP.NET MVC only allows you to POST objects to Actions in the Controller, where the Action's arguments accept the posted object as a Concrete class.
Is there any way around this, or a good alternative?
In my case, I have an action which accepts an interface as an argument:
public ActionResult SaveAdjustment(IModel model)
{
switch (model.SubsetType)
{
// factory like usage
}
}
And for this action, I have numerous views, all strongly typed to objects that implement IModel, all which I want to be able to post to this one method.
Of course, running this give me the error:
Cannot create an instance of an interface
Is there a nice work around to this? Or do I need to create an Action method for each and send them over to a method like this?
MVC generally binds models when posting from Request.Form, that is collection of name=value pairs. The reason that in default implementation there's no support of binding interfaces or abstract classes is obvious - mvc cannot determine which concrete class to create from name=value pairs. If you got hidden field on client side, or any other parameter anywhere by which you are able to determine which type of concrete class to create, you can simply create custom model binder. I believe you can override DefaultModelBinder's CreateModel method and reuse all other built in binding functionality
public class IModelModelBinder : DefaultModelBinder
{
protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, System.Type modelType)
{
//Create and return concrete instance
}
}
And model binder registration in global.asax
ModelBinders.Binders.Add(typeof(IModel?), new IModelModelBinder());
Actually, controllers and actions in mvc are meant to be thin, and some kind of service layer should be thick. As action logic you are trying to implement may get complicated soon, I would recommend moving it into separate service.
Although I mentioned this as a possible solution in my original question, its the solution I have gone with in the end and I actually quite like it now. This way I didn't need to touch the model default binding implementation and I think this approach is a more readable/understandable approach than what I was originally asking for.
In case its not clear why I wanted to go for this approach, I have added an example of how I can use this for its OO benifits.
[HttpPost]
public ActionResult SaveModelA(ModelA model)
{
return SaveModel(model);
}
[HttpPost]
public ActionResult SaveModelB(ModelB model)
{
return SaveModel(model);
}
private ActionResult SaveModel(IModel model)
{
IExampleService exampleService;
IRequirements requirements;
switch (model.SubsetType)
{
case SubsetType.ModelA:
myService = new ModelAService();
requirements = new ModelARequirements
{
ModelASpecificProperty = "example"
};
break;
case SubsetType.ModelB:
myService = new ModelBService();
requirements = new ModelBRequirements
{
ModelBSpecificProperty1 = "example",
ModelBSpecificProperty2 = "example2",
ModelBSpecificProperty3 = "example3"
};
break;
default:
throw new InvalidEnumArgumentException();
}
var serviceResonse = exampleService.ExecuteExample(model, requirements);
return RedirectToAction("Index", new
{
ExampleData = serviceResponse.ExampleDate
});
}
In case it isn't clear in the code:
ModelA : IModel
ModelB : IModel
ModelARequirements : IModelRequirements
ModelBRequirements : IModelRequirements
ModelAService : IExampleService
ModelBService : IExampleService
// and IModel defines a property SubsetType SubsetType { get; }
Our ASP.NET MVC application allows an authenticated user to administer one or more "sites" linked to their account.
Our Urls are highly guessible since we use the site friendly name in the URL rather than the Id e.g:
/sites/mysite/
/sites/mysite/settings
/sites/mysite/blog/posts
/sites/mysite/pages/create
As you can see we need access to the site name in a number of routes.
We need to execute the same behaviour for all of these actions:
Look for a site with the given identifier on the current account
If the site returned is null, return a 404 (or custom view)
If the site is NOT null (valid) we can carry on executing the action
The current account is always available to us via an ISiteContext object. Here is how I might achieve all of the above using a normal route parameter and performing the query directly within my action:
private readonly ISiteContext siteContext;
private readonly IRepository<Site> siteRepository;
public SitesController(ISiteContext siteContext, IRepository<Site> siteRepository)
{
this.siteContext = siteContext;
this.siteRepository = siteRepository;
}
[HttpGet]
public ActionResult Details(string id)
{
var site =
siteRepository.Get(
s => s.Account == siteContext.Account && s.SystemName == id
);
if (site == null)
return HttpNotFound();
return Content("Viewing details for site " + site.Name);
}
This isn't too bad, but I'm going to need to do this on 20 or so action methods so want to keep things as DRY as possible.
I haven't done much with custom model binders so I wonder if this is a job better suited for them. A key requirement is that I can inject my dependencies into the model binder (for ISiteContext and IRepository - I can fall back to DependencyResolver if necessary).
Many thanks,
Ben
Update
Below is the working code, using both a custom model binder and action filter. I'm still not sure how I feel about this because
Should I be hitting my database from a modelbinder
I can actually do both the retrieving of the object and null validation from within an action filter. Which is better?
Model Binder:
public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
if (!controllerContext.RouteData.Values.ContainsKey("siteid"))
return null;
var siteId = controllerContext.RouteData.GetRequiredString("siteid");
var site =
siteRepository.Get(
s => s.Account == siteContext.Account && s.SystemName == siteId
);
return site;
}
Action Filter:
public class ValidateSiteAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
var site = filterContext.ActionParameters["site"];
if (site == null || site.GetType() != typeof(Site))
filterContext.Result = new HttpNotFoundResult();
base.OnActionExecuting(filterContext);
}
}
Controller Actions:
[HttpGet]
[ValidateSite]
public ActionResult Settings(Site site)
{
var blog = site.GetFeature<BlogFeature>();
var settings = settingsProvider.GetSettings<BlogSettings>(blog.Id);
return View(settings);
}
[HttpPost]
[ValidateSite]
[UnitOfWork]
public ActionResult Settings(Site site, BlogSettings settings)
{
if (ModelState.IsValid)
{
var blog = site.GetFeature<BlogFeature>();
settingsProvider.SaveSettings(settings, blog.Id);
return RedirectToAction("Settings");
}
return View(settings);
}
This definitely sounds like a job for an action filter. You can do DI with action filters not a problem.
So yeah, just turn your existing functionality into a action filter and then apply that to each action OR controller OR a base controller that you inherit from.
I don't quite know how your site works but you could possibly use a global action filter that checks for the existence of a particular route value, e.g. 'SiteName'. If that route value exists, that means you need to follow through with checking that the site exists...
A custom model binder for your Site type sounds like a good idea to me.
You will probably also want an action filter as well to catch "null" and return not found.
I want to use a custom action filter to handle specific exceptions from my service classes to populate the model state and then return the view.
For example, take my previous code:
public ActionResult SomeAction(SomeViewModel model)
{
try
{
_someService.SomeMethod(model);
}
catch (ServiceException ex)
{
ModelState.AddModelError(ex.Key, ex.ErrorMessage);
}
return View();
}
Basically, it would call a service, and if a ServiceException was thrown, it would know that there was an issue w/ the model data, and add the error to the ModelState, then just return the view. But I noticed some very un-DRY-like patterns, because I had this same try/catch code in every action method.
So, to DRY it up a bit, I basically created a new HandleServiceError action filter:
public class HandleServiceErrorAttribute : HandleErrorAttribute
{
public override void OnException(ExceptionContext context)
{
((Controller)context.Controller)
.ModelState
.AddModelError(
((ServiceException)context.Exception).Key,
((ServiceException)context.Exception).ErrorMessage
);
context.ExceptionHandled = true;
}
}
Then simplified my action methods like so:
public ActionResult SomeAction(SomeViewModel model)
{
_someService.SomeMethod(model);
return View();
}
Problem is, once the action filter handles the error, it doesn't return to my action method. I sort of understand, under the hood, why this is happening. But I would still like to figure out a way to do what I'm trying to do.
Is this possible?
Thanks in advance.
UPDATE:
I tried the suggestions from the article Darin provided in his answer, but ran into issues trying to use constructor injection with the controller's model state.
For example, if you look at their Controllers\ProductController.cs code, they have the controller's empty constructor using a service locator to create the service, passing in the controller's ModelState at that point:
public ProductController()
{
_service = new ProductService(new ModelStateWrapper(this.ModelState),
new ProductRepository());
}
But if you look at the injected constructor, it assumes the ModelState will be injected into the constructor for the service:
public ProductController(IProductService service)
{
_service = service;
}
I don't know how to get CI to work with the current controller's ModelState. If I could figure this out, then this approach may work.
You could still return the corresponding view:
context.Result = new ViewResult
{
ViewName = context.RouteData.GetRequiredString("action")
};
You may also take a look at the following article for an alternative about how to perform validation at the service layer.
I have a BaseViewModel that my View Models all inherit from.
public class MagazineViewModel : BaseOutputViewMode
{
public string TitleOfPublication { get; set; }
}
In my controller I use a factory method to give the corret View Model back based on an input:
// e.g. viewModel contains an instance of MagazineViewModel
BaseOutputViewModel viewModel = BaseOutputViewModel.GetOutputViewModel(output);
When I use TryUpdateModel to try and bind to a FormCollection which I know contains a "TitleOfPublication" key, its never set in my view model:
if (!TryUpdateModel(viewModel, form))
I think this is something to do with the DefaultModelBinder using the BaseOutputViewModel to bind FormCollection keys to - it doesn't contain a "TitleOfPublication", the derived MagazineViewModel does.
I'm trying to roll my own model binder, to override the DefaultModelBinder's BindModel behavior. Its all wired in correctly and I can debug into it straight after the TryUpdateModel call:
public class TestModelBinder : DefaultModelBinder, IFilteredModelBinder
{
public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
// Tried the following without success ....
// 1. Quick hardcoded test
// bindingContext.ModelType = typeof(MagazineViewModel);
// 2. Set ModelMetadata, hardcoded test again
// bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, typeof(MagazineViewModel));
// 3. Replace the entire context
// ModelBindingContext context2 = new ModelBindingContext();
// context2.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, typeof(MagazineViewModel));
// context2.ModelName = bindingContext.ModelName;
// context2.ModelState = bindingContext.ModelState;
// context2.ValueProvider = bindingContext.ValueProvider;
// bindingContext = context2;
}
}
But I'm not sure how to work with the bindingContext? What needs to be updated so that I can tell the DefaultModelBinder to bind using the derived View Model properties?
Or have I just totally mis-understood this!
I did try overriding CreateModel - much like the DerivedTypeModelBinder in MvcContrib, but I think because I'm giving the binder an instance of a model to work with, CreateModel is never called. Used Reflector on the Mvc DLL, theres a "BindComplexModel" that calls CreateModel only if the model is null:
if (model == null)
{
model = this.CreateModel(controllerContext, bindingContext, modelType);
}
Any pointers greatfully received!
Cheers
OK - finally got to the bottom of this!
In actual fact there was nothing wrong with my model binder, the problem ultimately led back to a couple of input tags that had no name/id:
<input id="" name="" type="text">
The crux was this test in DefaultModelBinder:
// Simple model = int, string, etc.; determined by calling TypeConverter.CanConvertFrom(typeof(string))
// or by seeing if a value in the request exactly matches the name of the model we're binding.
// Complex type = everything else.
if (!performedFallback) {
ValueProviderResult vpResult =
bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
if (vpResult != null) {
return BindSimpleModel(controllerContext, bindingContext, vpResult);
}
}
With no id/name, the form collection has a key of "" which means that the GetValue correctly returned the value for that field, continuing to bind as a simple model.
When an id/name are added, the form collection contains no key of "", (which is now the name of my model as we're using TryUpdateModel). This meant the DefaultModelBinder correctly treated my model as complexm successfully binding properties in my derived type!
Cheers
I'm having trouble trying to think what the best way is to recreate a database object in a controller Action.
I want to make use of ModelBinders so in my action I have access to the object via a parameter, rather than having to repeat code to get an object from the database based on an identifier parameter. So I was thinking of having a ModelBinder that performs a call to the dataaccess layer to obtain the original object (or creates a new one if it doesn't exist in the database), then binds any properties to the database object to update it. However I've read that the ModelBinders shouldn't make database queries (first comment of this article).
If the ModelBinder shouldn't perform a database query (so just using the DefaultModelBinder) then what about database objects that have properties that are other db objects? These would never get assigned.
Saving an object after the user has edited it (1 or 2 properties are editable in the view) the ModelBinded object would be missing data, so saving it as it is would result in data in the database being overwritten with invalid values, or NOT-NULL constraints failing.
So, whats the best way to get an object in a controller action from the database bound with the form data posted back from the view?
Note im using NHibernate.
I get the model object from the database, then use UpdateModel (or TryUpdateModel) on the object to update values from the form parameters.
public ActionResult Update( int id )
{
DataContext dc = new DataContext();
MyModel model = dc.MyModels.Where( m => m.ID == id ).SingleOrDefault();
string[] whitelist = new string[] { "Name", "Property1", "Property2" };
if (!TryUpdateModel( model, whitelist )) {
... model error handling...
return View("Edit");
}
ViewData.Model = model;
return View("Show");
}
Unfortunately you don't have control over the construction of the model binder, so you can't inject any repository implementation.
You can reach out directly into a service locator to pull in your repository & fetch the item:
public class ProductBinder : DefaultModelBinder
{
protected override object CreateModel(ControllerContext controllerContext,
ModelBindingContext bindingContext, Type modelType)
{
if(modelType != typeof(Product))
return null;
var form = controllerContext.HttpContext.Request.Form;
int id = Int32.Parse(form["Id"]);
if(id == 0)
return base.CreateModel(controllerContext, bindingContext, modelType);
IProductRepository repository = ServiceLocator.Resolve<IProductRepository>();
return repository.Fetch(id);
}
}
You might even make this work for all of your entities if you can use a base class or interface that provides the Id of the class.
You'll have to set this up in Global.asax:
ModelBinders.Binders.Add(typeof(Product), new ProductBinder());
and then you can do this:
public ActionResult Save([Bind] Product product)
{
....
_repository.Save(product);
}
Let me first state that I don't recommend to access database from ModelBinders, as from perspective of Separation Of Concern ModelBinders should only be responsible of interpretting client request, obviously database is not.
If you dont want to repeat your self (DRY), use repositories/services
However if u really want to do it like that, then
In global.asax.cs Register a custom MyModelBinderProvider to MVC
ModelBinderProviders.BinderProviders.Add(new EntityModelBinderProvider
{
ConnectionString = "my connection string"
));
Cunstruct the custom ModelBinderProvider to contain database settings
public class EntityBinderProvider: IModelBinderProvider
{
public string ConnectionString { get; set; }
public IModelBinder GetBinder(Type modelType)
{
if (Is known entity)
return new EntityBinder(ConnectionString);
else
return null;
}
}
Follow further instructions from Ben Scheirman
You don't actually have to hit the database. Simply setting the Id of the objects will be enough to set the relationship up, but watch your cascades. Make sure your cascde settings won't update the related object as it will clear the values.