I am working on a multi-tenant .NET Core app where all the validations needs to be dynamic (Db Driven). How can I implement custom model validation?
You can use Remote Validation for validations where you need to go to the server (and then the db). You need to specify the action and the controller and it will be called during validation from the client side through AJAX. Then on the server side, you can do whatever you need in order to validate. In your case you will need to check the database. Here is an example:
public class User
{
[Remote(action: "VerifyEmail", controller: "Users")]
public string Email { get; set; }
}
The above is using the Remote attribute and specifying to use VerifyEmail action of the Users controller. In UsersController class you will have something like this:
[AcceptVerbs("Get", "Post")]
public IActionResult VerifyEmail(string email)
{
if (!_userRepository.VerifyEmail(email))
{
return Json(data: $"Email {email} is already in use.");
}
return Json(data: true);
}
The MVC framework will take care of all the AJAX(ing) for you so you do not need to worry about any of that. I have used this many times before and it works really well.
Related
Rails has a very convenient uniqueness validation.
ASP.NET MVC doesn't.
I need to make sure that the e-mail address a user has entered hasn't been registered by anyone yet.
I can see only one way of doing this kind of validation: create a new data context object in the UniqueAttribute class.
But I'm afraid that wasting memory on a new data context object just for one validation is dangerous.
Am I wrong? Is there a better way to do that?
Update
This is what I got so far
public class UniqueEmailAttribute : ValidationAttribute {
public override bool IsValid(object value) {
DataContext db = new DataContext();
var userWithTheSameEmail = db.Users.SingleOrDefault(
u => u.Email == (string)value);
return userWithTheSameEmail == null;
}
}
// Usage
[UniqueEmail(ErrorMessage="This e-mail is already registered")]
public string Email { get; set; }
There are two problems.
It would be good to have just one UniqueAttribute class, not separate classes for e-mails, usernames etc. How can I do that?
Creating a new data context every time you need to validate a single attribute.
SOLUTION
So in the end I created a unique constraint on the table and now I just have to intercept SqlException in Users repository. Works great and is probably more efficient than searching for the same node in the whole table. Thanks!
Mvc 3 Relaease candidate has new New Validation Attributes as a remotevalidation -where you can register a method for validation on clientside(jquery).
see below example-
RemoteAttribute
The new RemoteAttribute validation attribute takes advantage of the jQuery Validation plug-in's remote validator, which enables client-side validation to call a method on the server that performs the actual validation logic.
In the following example, the UserName property has the RemoteAttribute applied. When editing this property in an Edit view, client validation will call an action named UserNameAvailable on the UsersController class in order to validate this field.
public class User {
[Remote("UserNameAvailable", "Users")]
public string UserName { get; set; }
}
The following example shows the corresponding controller.
public class UsersController {
public bool UserNameAvailable(string username) {
return !MyRepository.UserNameExists(username);
}
}
Mvc 3
UPDATE
public bool UserNameAvailable(string Propertyname)
{
if (Request.QueryString[0]= "UserName")
{
//validate username
}
elseif (Request.QueryString[0]= "Email")
{
//Validate Email
}
}
ASP.Net does have a feature that can automatically check the uniqueness of a user's email address when a user registers. It is the ASP.Net Membership service and you can use it to do what you want even if you don't use all of the features of it.
If you are not using the full Membership feature in your MVC application, then all you need to do is use
Membership.FindUsersByEmail(emailYouAreLookingFor);
If any values come back, you know that the address is not unique. If you ARE using the Membership service to create users, then the Membership service will check AUTOMATICALLY and return a code to you if the user's email address is not unique.
The Membership service sits in the System.Web.Security area so you would need a
using System.Web.Security;
reference in your controller.
Here is an example
MembershipCreateStatus createStatus = MembershipService.CreateUser(UserName, Password, Email);
if (createStatus == MembershipCreateStatus.DuplicateEmail)
{
//do something here
}
else
{
//do something here
}
I hope this helps!
The right way to make a generic remote unique validator in MVC can be found in this MVC forum. by counsellorben. It's based on my MVC unique remote validator article http://msdn.microsoft.com/en-us/library/gg508808(VS.98).aspx
A foolproof way of doing this is to create a validation attribute that would query the database for the email address. It would certainly add latency.
An alternative would be to create a unique constraint on the table and intercept SqlException.
I've made a custom model, and I want to mock it. I'm fairly new to MVC, and very new to unit testing. Most approaches I've seen create an interface for the class and then make a mock that implements the same interface. However I can't seem to get this to work when actually passing the interface into the View. Cue "simplified" example:
Model-
public interface IContact
{
void SendEmail(NameValueCollection httpRequestVars);
}
public abstract class Contact : IContact
{
//some shared properties...
public string Name { get; set; }
public void SendEmail(NameValueCollection httpRequestVars = null)
{
//construct email...
}
}
public class Enquiry : Contact
{
//some extra properties...
}
View-
<%# Page Language="C#" Inherits="System.Web.Mvc.ViewPage<project.Models.IContact>" %>
<!-- other html... -->
<td><%= Html.TextBoxFor(model => ((Enquiry)model).Name)%></td>
Controller-
[HttpPost]
public ActionResult Index(IContact enquiry)
{
if (!ModelState.IsValid)
return View(enquiry);
enquiry.SendEmail(Request.ServerVariables);
return View("Sent", enquiry);
}
Unit Testing-
[Test]
public void Index_HttpPostInvalidModel_ReturnsDefaultView()
{
Enquiry enquiry = new Enquiry();
_controller.ModelState.AddModelError("", "dummy value");
ViewResult result = (ViewResult)_controller.Index(enquiry);
Assert.IsNullOrEmpty(result.ViewName);
}
[Test]
public void Index_HttpPostValidModel_CallsSendEmail()
{
MockContact mock = new MockContact();
ViewResult result = (ViewResult)_controller.Index(mock);
Assert.IsTrue(mock.EmailSent);
}
public class MockContact : IContact
{
public bool EmailSent = false;
void SendEmail(NameValueCollection httpRequestVars)
{
EmailSent = true;
}
}
Upon a HttpPost I get a "Cannot create an instance of an interface" exception. I seems that I can't have my cake (passing a model) and eat it (pass mock for unit testing). Maybe there's a better approach to unit testing models bound to views?
thanks,
Med
I'm going to throw it out there, if you need to mock your models you're doing it wrong. Your models should be dumb property bags.
There is absolutely no reason that your model should have a SendEmail method. That is functionality that should be invoked from a controller calling to an EmailService.
Responding to your question:
After years of working with Separation of Concern (SOC) patterns like MVC, MVP, MVVM and seeing articles from people brighter than me (I wish I could find the one I'm thinking off about this but maybe I read it in a magazine). You will eventually conclude in an enterprise application you will end up with 3 distinct sets of model objects.
Previously I was a very big fan of doing Domain Driven Design (DDD) using a single set of business entities that were both plain old c# objects (POCO) and Persistent Ignorant (PI). Having domain models that are POCO/PI leaves you with a clean slate of objects where there is no code related to accessing the object storage or having other attributes that have schematic meaning for only 1 area of the code.
While this works, and can work fairly well for a period of time, there is eventually a tipping point where the complexity of expressing the relationship between View, Domain Model, and Physical Storage Model becomes too complex to express correctly with 1 set of entities.
To solve the impedance mismatches of View, Domain and Storage you really need 3 sets of models. Your ViewModels will exactly match your views binding to facilitate it to be easy to work with the UI. So this will frequently have things such as adding a List to populate drop downs with values that are valid for your edit view/action.
In the middle is the Domain Entities, these are the entities that you should validate against your business rules. So you will map to/from them on both sides to/from the view and to/from the storage layer. In these entities is where you could attach your code to do validation. I personally am not a fan of using attributes and coupling validation logic into your domain entities. It does make alot of sense to couple validation attributes into your ViewModels to take advantage of the built in MVC client side validation functionality.
For validation I would recommend using a library like FluentValidation (or your own custom one, they're not hard to write) that lets you separate your business rules from your objects. Although with new features with MVC3 you can do remote validation severside and have it display client side, this is an option to handle true business validation.
Finally you have your storage models. As I said previously I was very zealous on having PI objects being able to be reused through all layers so depending on how you setup your durable storage you might be able to directly use your domain objects. But if you take advantage of tools like Linq2Sql, EntityFramework (EF) etc you will most likely have auto generated models with code for interacting with the data provider so you will want to map your domain objects to your persistence objects.
So wrap all of this up this would be a standard logic flow in MVC actions
User goes to edit product page
EF queries the database to get the existing product information, inside the repository layer the EF data objects are mapped to the Business Entities (BE) so all the data layer methods return BEs and have no external coupling to the EF data objects. (So if you ever change your data provider you don't have to alter a single line of code except for the internal implementation)
The controller gets the Product BE and maps it to a Product ViewModel (VM) and adds collections for the different options that can be set for drop down lists
Return View(theview, ProductVM)
User edits the product and submits the form
Client side validation is passed (useful for date validation / number validation instead of having to submit the form for feedback)
The ProductVM gets mapped back to ProductBE at this point you would validate the business rules along the lines ValidationFactory.Validate(ProductBE), if it's invalid return messages back to view and cancel edit, otherwise continue
You pass the ProductBE into your repository model, inside the internal implementation of the data layer you map the ProductBE to the Product Data Entity for EF and update the database.
2016 edit: removed usages of Interface as separation of concerns and interfaces are entirely orthogonal.
Your issue is here:
public ActionResult Index(IContact enquiry)
MVC in the background has to create a concrete type to pass to the method when calling it. In this method's case, MVC needs to create a type which implements IContract.
Which type? I dunno. Neither does MVC.
Instead of using interfaces in order to be able to mock your models, use normal classes that have protected methods which you can override in mocks.
public class Contact
{
//some shared properties...
public string Name { get; set; }
public virtual void SendEmail(NameValueCollection httpRequestVars = null)
{
//construct email...
}
}
public class MockContact
{
//some shared properties...
public string Name { get; set; }
public bool EmailSent {get;private set;}
public override void SendEmail(NameValueCollection vars = null)
{
EmailSent = true;
}
}
and
public ActionResult Index(Contact enquiry)
It is possible to use interfaces.
See: http://mvcunity.codeplex.com/
Ok I've just ran into this and I was only supposed to be checking my emails however I've ended up watching this (and not far off subscribing to TekPub).
http://tekpub.com/production/starter
Now this app is a great starting point, but it raises one issue for me and the development process I've been shown to follow (rightly or wrongly). There is no conversion from the LinqToSql object when passing data to the view. Are there any negitives to this?
The main one I can see is with validation, does this cause issues when using MVC's built in validation as this is somthing we use extensivly. Because we are using the built in objects generated by LinqToSql how would one go about adding validation, like
[Required(ErrorMessage="Name is Required")]
public string Name {get;set;}
Interested to understand the benifits of this methodology and any negitives that, should we take it on, experiance through the development process.
Should this be taken as a guide and we should be using ViewModels? If so should we always use them even in simple cases? And how/where in the application logic does the Entity get converted to a ViewModel?
With entity objects, you could use buddy classes, whereby you create a second class which acts as a metadata provider for your entity. For instance, with a Customer entity generated by Linq-to-Sql, I could create a buddy class like so:
[MetadataType(typeof(CustomerMeta))]
partial class Customer {
}
public class CustomerMeta {
[DisplayName("Forename", Required(ErrorMessage = "Forename is required.")]
public string Forename { get; set;}
}
Entities are generated as partial classes so you can add your own code to them.
Alternatively, you could forego pushing your entity types to your views and create specific models based around the functionality required, for instance I would typically have a User entity, but when I need to create a User, I have something called a CreateUserSpec model:
public class CreateUserSpec
{
[DisplayName("Forename")]
public string Forename { get; set; }
}
Which has a subset of the properties of the User, only those required to create a User. This is the model I would pass to my view, and repopulate from the form data. For instance:
public class AccountController
{
public ActionResult Register() {
return View(new CreateUserSpec());
}
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Register(CreateUserSpec spec) {
if (!ModelState.IsValid) {
return View(spec);
}
var user = UserFactory.CreateUser(spec);
// Redirect to authorisation page?
}
}
Suppose I have this model:
public class ViewModel
{
[Required]
public string UserInput { get; set; }
[Required]
public Guid EntityId { get; set; }
}
Now, when UserInput is wrong, I want to re-display the same page but with validation errors (e.g. /Edit). However, when EntityId is wrong, I want to redirect to some other page (e.g. /Create).
I can do this manually inside each controller...
if (!ModelState.IsValidField("EntityId")) { redirect }
//or
if (string.IsNullOrEmpty(data.EntityId)) { redirect }
but it's kind of boring and violates DRY. Imaging several entities, nested view models with entities... too cumbersome. I'd better have something like ModelState.IsValidUserData and ModelState.IsValidCriticalData. But there's no such thing.
Now, EntityId is actually bound using my custom model binder, that knows that it is mission-critical. So there's this solution:
Usual fields do populate ModelState with errors as usual.
(a) Critical fields are bound using custom model binder that throws special "CriticalModelErrorException". Controller actions have [HandleCrirticalError("action", "controller')] attribute - which handles critical errors and redirects to the given action.
(b) Critical fields are bound using custom model binder that sets BaseController.CriticalModelErrors property (obviously all controllers are derived from supercontroller base class). Each action is free to check both ModelState.IsValid and base.CriticalModelErrors and behave freely based on that.
(c) Critical fields are bound using custom model binder that sets special-format model state errors, e.g. AddModelError(name, "!CRITICAL! text"; Then base controller have method that detects such strings.
2a example:
[HandleCriticalError("Create")] // uses the same controller
[HandleModelStateError("Edit")] // redisplays page with validation errors
public ActionResult Edit(ViewModel data)
{
// here we know both our data entities and user data are valid and safe
}
2b example
public ActionResult Edit(ViewModel data)
{
if (!ModelState.IsValid)
return View(data);
if (base.CriticalModelErrors.Count > 0)
return RedirectToAction("Create");
// here we know both our data entities and user data are valid and safe
}
2c example
protected bool HasCriticalErrors()
{
return ModelState.Any(x => x.Value.Errors.Any(x => x.ErrorMessage.StartsWith("!CRITICAL!")))
}
// then same as 2b
Now, the questions: how it's handled by other apps and developers (you and your apps)? Which one would you prefer? Are there any drawbacks or better solutions?
Use the one that introduces the most amount of automation for you, so you won't have to repeat the same code on my places. As you have done already I'd go with 2a but make it a bit different so I wouldn't put those attributes on every single action but rather on the whole Controller class. If at all possible (if required by at least majority actions). If you need to exclude certain actions, create a separate action filter that will disable redirecting.
Related: What’s the best way to implement field validation using ASP.NET MVC?
Let's suppose a solution with the following projects:
Foo; // the MVC web project
Foo.Models;
Foo.Repositories;
Foo.Services;
Foo.Models is the domain of the application with all the entities, doesn't matter if using EF, NH, POCO or whatever. Here's an example:
public class User
{
public string Username { get; set; }
public string Email { get; set; }
public string Password { get; set; }
}
In Foo.Repositories there is a UserRepository and in Foo.Services there is a UserService.
In the web application let's consider a model binder like following:
public class UserBinder : DefaultModelBinder
{
//...
}
I see three different options on where to put the validation:
In Foo.Models like the following:
public class User
{
public string Username { get; set; }
public string Email { get; set; }
public string Password { get; set; }
public ICollection<KeyValuePair<string, string>> ValidateErrors()
{
//Validate if Username, Email and Password has been passed
}
}
In Foo.Services like:
public class UserService
{
public ICollection<KeyValuePair<string, string>> ValidateErrors()
{
//Validate if Username, Email and Password has been passed
}
}
In Foo inside the model binder:
public class UserBinder : DefaultModelBinder
{
protected override void OnModelUpdated(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
var user = (User)bindingContext.Model;
// validate everything here
base.OnModelUpdated(controllerContext, bindingContext);
}
}
Another thing to notice is that considering the first 2 options [Model and Service] there is another decision to make: ValidateErrors method can be called directly on the controller or inside the Binder.
I have 2 questions on the scenario:
Should the validation be:
In the Model being called from the controller?
In the Model being called from the binder?
In the Service being called from the controller?
In the Service being called from the binder?
Directly in the Binder?
Any other idea?
All the above scenario discuss about the User creation. But what about User logon?
Let's say user uses the username and password to login in the application, so it won't need to validate the e-mail.
Where this validation should be?
In the Model being called from the controller?
In the Service being called from the controller?
Any other idea?
Check out the ASP.NET MVC Contact Manager Sample Application it has a very good architecture im my opinion
http://www.asp.net/learn/mvc/tutorial-26-cs.aspx'>http://www.asp.net/learn/mvc/tutorial-26-cs.aspx
I'm a big fan of putting calling the validation from the controllers and having the validation routine return an ActionResult so the controller can know what to do with the result.
For what it's worth, here's what I have scrounged up in my current project:
I have Models, Repositories (you can call them Services if you like), and ViewModels. I try to avoid writing custom model binders because (a) it's boring and (b) a strange place to put validation, IMHO. To me, a model binder is just taking items from the request and shoving them into an object. PHP, for example, doesn't do any validation when plucking items from a header into the $_POST array; it's the thing we plug the array into that cares about its contents.
My Model objects generally never allow themselves to enter an invalid state. This means that required parameters are passed in during constructors and properties will throw exceptions if they're attempted to be set with invalid values. And, in general, I try to design my Model objects to be immutable. For example, I have an Address object for mailing addresses that is constructed with an AddressBuilder object with looks at the field requirements for a given country by inspecting an AddressScheme that can be retrieved from the AddressSchemeRepository. Phew. But I think it's a good example because it takes something conceptually simple ("validate a mailing address") and makes it complicated in real world usage ("we accept addresses from over 30 countries, and those formatting rules are sitting in a database, not in my code").
Since constructing this Model object is kind of a pain--as well it should be, since it's being quite particular about the data that gets loaded into it--I have a, say, InputAddressViewModel object that my view binds to. The InputAddressViewModel implements IDataErrorInfo so that I get ASP.NET MVC's DefaultModelBinder to add errors to the ModelState automatically. For simple validation routines that I know ahead of time (phone number formatting, first name required, e-mail address format), I can implement these right in the InputAddressViewModel.
The other advantage of having a view model is that because it is shamelessly tailored to a particular view, your real model is more reusable because it doesn't have to make any weird concessions to make it suitable for UI display (e.g., needs to implement INotifyPropertyChanged or Serializable or any of that mess).
Other validation errors about the address I won't know about until I interact with my AddressScheme in my actual Model. Those errors will be there controller's job of orchestrating into the ModelState. Something like:
public ActionResult InputAddress(InputAddressViewModel model)
{
if (ModelState.IsValid)
{
// "Front-line" validation passed; let's execute the save operation
// in the our view model
var result = model.Execute();
// The view model returns a status code to help the
// controller decide where to redirect the user next
switch (result.Status)
{
case InputAddressViewModelExecuteResult.Saved:
return RedirectToAction("my-work-is-done-here");
case InputAddressViewModelExecuteResult.UserCorrectableError:
// Something went wrong after we interacted with the
// datastore, like a bogus Canadian postal code or
// something. Our view model will have updated the
// Error property, but we need to call TryUpdateModel()
// to get these new errors to get added to
// the ModelState, since they were just added and the
// model binder ran before this method even got called.
TryUpdateModel(model);
break;
}
// Redisplay the input form to the user, using that nifty
// Html.ValidationMessage to convey model state errors
return View(model);
}
}
The switch may seem repulsive, but I think it makes sense: the view model is just a plain old class and doesn't have any knowledge of the Request or the HttpContext. This makes the logic of the view model easy to test in isolation without resorting to mocking and leaves the controller code left to, well, control by interpreting the model's result in a manner that makes sense on a Web site--it could redirect, it could set cookies, etc.
And the InputAddressViewModel's Execute() methods looks something like (some people would insist on putting this code into a Service object that the controller would call, but to me the view model will do so much finagling of the data to make it fit the real model that it makes sense to put it here):
public InputAddressViewModelExecuteResult Execute()
{
InputAddressViewModelExecuteResult result;
if (this.errors.Count > 0)
{
throw new InvalidOperationException(
"Don't call me when I have errors");
}
// This is just my abstraction for clearly demarcating when
// I have an open connection to a highly contentious resource,
// like a database connection or a network share
using (ConnectionScope cs = new ConnectionScope())
{
var scheme = new AddressSchemeRepository().Load(this.Country);
var builder = new AddressBuilder(scheme)
.WithCityAs(this.City)
.WithStateOrProvinceAs(this.StateOrProvince);
if (!builder.CanBuild())
{
this.errors.Add("Blah", builder.Error);
result = new InputAddressViewModelExecuteResult()
{
Status = InputAddressViewModelExecuteStatus
.UserCorrectableError
};
}
else
{
var address = builder.Build();
// save the address or something...
result = new InputAddressViewModelExecuteResult()
{
Status = InputAddressViewModelExecuteStatus.Success,
Address = address
};
}
}
return result;
}
Does this make sense? Is it a best practice? I have no idea; it's certainly verbose; it's what I just came up with in the past two weeks after thinking about this problem. I think you're going to have some duplication of validation--your UI can't be a complete imbecile and not know what fields are required or not before submitting them to your model/repositories/services/whatever--otherwise the form could simply generate itself.
I should add that the impetus for this is that I've always kind of detested the Microsoft mentality of "set one property -> validate one property" because nothing ever works like that in reality. And you always end up getting an invalid object persisted because someone forgot to call IsValid or some such on the way to the data store. So another reason for having a view model is that it tailors itself to this concession so we get a lot of CRUD work of pulling items from the request, validation errors in the model state, etc quite easily without having to compromise the integrity of our model itself. If I have an Address object in hand, I know it's good. If I have an InputAddressViewModel object in hand, I know I need to call it's Execute() method to get that golden Address object.
I'll look forward to reading some of the other answers.
After a lot of research I think I got the answers to my question so i decided to share.
The validation code should be on Model.
As per the idea of "thin controller, fat model" AND considering that a model would know what it needs to validate or not.
For example, let's say I decide to user the Foo.Models in other solution but I decide NOT to use any other project and the validation is in other project.
I'll have to re-code the entire validation in this case what is a total waste of time, right?
OK. The validation code must be in the model but where should it be called?
This validation must be called where you're saving it to your database or file.
As in the proposed scenario I'm considering the repository as a domain, then we should consider putting the validation just before the change saving [in this example I'm using Entity Framework but it's not necessary, it's just to show]:
public class UserRepository : IRepository<User>
{
public void Create(User user)
{
user.Validate();
var db = dbFooEntities();
db.AddToUsers(user);
db.SaveChanges();
}
}
As per MS recommendation, the model validation should raise an exception and the controller must populate the ModelState with the errors found [I'll try to update this answer with a sample code on that as soon as I finish my app].
With that we have an answer for question #1.
What about question #2, regarding the login validation?
As login is not a situation where you're persisting your data, the validation should stay on the Service since logging in is a service in this case.
So, the answers for the question are:
In the Model being called from the REPOSITORY [that is called by the controller]
In the Service being called from the controller
This is very interesting and it helps me a lot in deciding where to put validation.
currently I feel the most for each model implementing a "Validate" method, which is called from a Repository or a Service.
However, what about validating if a chosen username is unique?
Should that code be inside the User model, or inside the UserService class, or in the UserRepository class?
If the uniqueness validation should be inside the User model, then the User model should have access to either the UserService or the UserRepository class. Is that OK, or is that against any "best practice" pattern?
For example:
class User
{
string Username { get; set; }
string Email { get; set; }
string Password { get; set; } // hashed and salted of course :)
IEnumerable<RuleViolation> Validate()
{
List<RuleViolation> violations = new List<RuleViolation>();
IUserService service = MyApplicationService.UserService; // MyApplicationService is a singleton class, especialy designed so that the User model can access application services
// Username is required
if ( string.IsNullOrEmpty(Username) )
violations.Add(new RuleViolation("Username", "Username is required"));
// Username must be unique: Should uniqueness be validated here?
else if( !service.IsUsernameAvailable(Username)
violations.Add(new RuleViolation("Username", "Username is already taken!"));
// Validate email etc...
return violations;
}
}
interface IUserRepository
{
void Save(User item);
}
interface IUserService
{
IUserRepository UserRepository { get; }
void Save(User item);
}
class UserService : IUserService
{
public UserService(IUserRepository userRepository)
{
this.UserRepository = userRepository;
}
IUserRepository UserRepository { get; private set}
public void Save(User user)
{
IEnumerable<RuleViolation> violations = user.Validate();
if(violations.Count() > 0)
throw new RuleViolationException(violations); // this will be catched by the Controller, which will copy the violations to the ModelState errors collection. But the question is, should we validat the user here, or in the UserRepository class?
UserRepository.Save(user);
}
}
class UserRepository : IUserRepository
{
void Save(User item)
{
IEnumerable<RuleViolation> violations = user.Validate();
if(violations.Count() > 0)
throw new RuleViolationException(violations); // this will be catched by the Controller, which will copy the violations to the ModelState errors collection. But the question is, should we validate the user here, or in the UserService class?
UserRepository.Save(user);
}
}
My guess would be that validation should be as close to the model as possible. So I'd say that the UserRepository should be the one responsible for validating it's model being added.
The most important queston for me is: Should the User model know about the IUserService / IUserRepository interfaces so that it can validate the Username uniqueness?
Or should the IUserService service validate uniqueness?
I'm curious about your views on this!
I'm using the DataAnnotations attributes in combination with a MVC model binder to do my validation and its pretty awesome. Since I treat User input as Command View Models its the cleanest way to keep domain clean from outside concerns.
http://bradwilson.typepad.com/blog/2009/04/dataannotations-and-aspnet-mvc.html
This also allows me to take advantage of AutoForm by LosTechies.com:
http://www.lostechies.com/blogs/hex/archive/2009/06/17/opinionated-input-builders-part-8-the-auto-form.aspx
And I expect the client side validation tools in MVC 2, VS 2010 to take advantage of these attributes as well.
So I'm whipping out user input view models, commands, at a furious pace right now and tying them into not only the AutoForm functionality but my own custom UI templates to get AutoGrid and AutoOutput from these attributes as well.
Nothing is better than saying:
Html.AutoForm(Model);
Or
Html.AutoGrid(Model.Products);
And getting validation and html generation in a very DRY and orthogonal way. My controllers are light, my domain pristine, and my time is unoccupied by writing the same if( string.IsNullOrEmpty() ) method on every object with a FirstName property.
For me the approach was not as "philosophical" as others have written about. I'm trying to be very pragmatic about MVC development and I get a ton of bang for the buck out of these bits.