First of all, I have to say that I understand how Data Annotation -based Model Validation works in ASP.NET MVC4 and I have it successfully implemented with DataAnnotationsModelValidatorProvider. So I don't need assistance on setting it up.
But when it comes down to HtmlHelpers, I'm struggling with trying to figure the context of the error message. And by saying context, I mean which error we're talking about. Which Attribute returned the error?
What I can get, is the Key for the error and the current ErrorMessage but programmatically, there's nothing, that at least I'm aware of, that would communicate which error we're talking about. Whether it was Required attribute or some other attribute, there's not way that I can find how to distinguish them.
Let's open the scenario a little bit. I have custom HtmlHelpers to render ContentEditable elements. For example Html.ContentEditableValidationMessageFor(m => m.firstName);. It will output something like this:
<span contenteditable="true" data-valmsg-for="firstName" data-valmsg-replace="Please provide first name" class="field-validation-error">Please provide first name</span>
Now, I do have a jQuery plugin to handle and persist the changes in the contenteditable element and it will persist them into the backend. However, the UI has nothing that would say which error message we're talking about. Humans can easily see it's the RequiredAttribute, but programmatically there's no data to differentiate it from some MinLengthAttribute for example.
In this scenario, if I would simply use the data-valmsg-for="firstName" as the key for the localization, that'd return the same error message for all the errors concerning the same property.
To Round it Up
What would be the Best Practise, when ModelState is available, to emit a unique ID for ModelError? Considering I'm using ASP.NET MVC4 and DataAnnotationsModelValidatorProvider.
I can think of tons of ways to "Hack it Together" but I would like to use the ModelState and whatever MVC provides. If it all goes down to writing a custom ModelValidatorProvider, then I'm all open for it. As long as it is the best and most sustainable way of going about it. I'm all for Doing More Now and Less Later than Hacking it Now and Hacking it Forever to Keep It Working
Can you give some context around the need to know which rule triggered the validation error, could it be a case of you trying to do something you shouldn't have too?
In general I use FluentValidation (http://fluentvalidation.codeplex.com/wikipage?title=mvc) in place of Data Annotation validation for many reasons, de-cluttering models, unit testing validation logic, allowing vastly more complex validation that include business logic. If your free to use 3rd party libraries I'd give it a look as it has always solved any validation problems I've had in the past.
It lets you write c# code that deals with your model validation via a fluent API. It has an MVC extension that wires everything up for you so other than creating the models validation class there is little impact from then on. An example for your code snippet above would be...
RuleFor(modelname => modelname.FirstName).NotEmpty().WithMessage("lease provide first name");
Even implementing ModelValidatorProvider will not help, it is just a mechanism to provide ModelValidators based on Model Metadata. When during model binding process in a controller action ModelValidators are being invoked the result is just ModelValidationResult which only contains MemberName and a text Message.
I think there is a dirty way to find out which ModelValidator is failed by checking the error message like this:
var modelErrors = ModelState.Where(m => m.Value.Errors.Count > 0).Select(m => new { Name=m.Key , Errors=m.Value.Errors});
by checking ErrorMessage of Errors for each key in modelErrors against ValidatorProvider error messages you can find out the error belongs to which Validator.
Related
I have a separate .dll with our database model and partial classes etc in using FluentValidation which works fine (it's to be used by both by desktop barcoding terminals and also by our website).
For the desktop apps I can read and display all errors like below
public override int SaveChanges()
{
var errors = this.GetValidationErrors();
if (errors.Any())
{
//handle validation errors
return 0;
}
else
{
return base.SaveChanges();
}
}
For the MVC site I can set up validators on individual models or create data annotations and get those working okay (which is not what I want). The thing I can't get my head around is how I can force my models to map to my entities in a way that I can display the fluent validation messages in the views. I don't want to have two separate sets of logic to be maintained and the barcoding apps and website must use the same.
Do I have to map my entities directly to the views? which i've been led to believe is a bad thing and not very flexible. Or is there a way of stating that a field in a model maps back to an attribute of one of my entities? perhaps an annotation of some description.
EDIT:
Just some clarification for the types of validation i'll need.
most front end input type validation will still stay in the viewModels (required/length/password matches etc - basically all the stuff I can use for client side validation as well). But there are all the business logic validations that I don't want there. Things like email addresses must be validated before other options can be set, account numbers must be of a particular format based on name (stuff I can't do with a regex). This particular date is not a valid delivery date etc.
I guess one thing I could do is add these to the ValidationSummary somehow and display them separate from the individual fields.
I think you're just looking at the situation wrong. What MVC is all about is a separation of concerns. There's things the database needs to know about that your views could care less, and vice versa. That's why the recommended practice is to use view model with your views and not the entity itself.
Validation is much the same. Something like the fact that a password confirmation needs to match the password the user entered does not concern the database at all. Or more appropriately, something like a validation on minimum amount of characters in the password does not concern the database, either; it will only ever receive a salted and hashed version of the password. Therefore it would be wrong to put this kind of validation on your entity. It belongs on the view model.
When I first started out using MVC, I used to add all the validation logic to my entity class and then go and repeat that same validation on my view model. Over time, I started to realize that very little of the validation actually needs to be on both. In fact, the largest majority of validation will should just go on your view model. It acts as a gatekeeper of sorts; if the data is good enough to get through your view model, it's good enough for your database. The types of validation that make sense on your entity is things like Required, but even that is really only necessary on a nullable field that must have a value by the time it gets to your database. Things like DateTimes are non-nullable by default, and EF is smart enough to make them non-nullable on the tables it creates by default. MaxLength is at times worthwhile if there should be a hard limit on the length of a text field in your database, but more often than not, nvarchars work just fine.
Anyways the point is that if you actually sit down and start evaluating the validation on your entity, you'll likely see that most of it is business logic that only applies to how your application works and not to how the data is represented at the database level. That's the key takeaway: on your entity, you only need the validation that's necessary for the database. And that's generally pretty thin.
Just an update. to get the two tier validation that i needed i had to mark all my entity model classes as IValidatable. Then i overrode the validate method for each class and invoked my fluent validation validator method there, passing back the errors needed. for the modelstate.addmodelerror i set the key as the field name and it mapped back okay. bit more code but it works. if i find a better way to do this ill update.
Background
I have a payment page where the user can select from a list of existing payment methods, or specify a new one. The dropdown presents options such as:
Visa - ******1234 (Saved)
Mastercard - ******9876 (Saved)
[New Credit Card ...]
[New Electronic Check ...]
Using jQuery, I toggle hidden DIVs that contain either an informational table (in the case of options 1 or 2 for saved payment methods) or a form (in the case of the [new] options).
I am using a strongly typed class as my view model which contains (among simple types) a CreditCard class and a Check class. Each of these classes uses data annotation validators, as they are used in other parts of the site.
Problem
The problem comes in when the user submits the form. I would like to use model binding to handle the mapping of POST values, but I need the binding and/or validation to fire depending on which option the user selected. For example, if the user selects option 1 or 2 from the list above, I don't want the model validation (or maybe even the binding itself) to fire for the CreditCard or Check objects.
I have researched the possibilities of creating a custom model binder using IModelBinder as well as extending the DefaultModelBinder and just overriding some of the methods. However, I am unsure as to which method is better, and, if extending DefaultModelBinder, which would be the appropriate method to override.
The logic would be fairly simple:
If the user selected one of the existing payment methods, no validation on the CreditCard or Check are required.
If the user selected one of the options to create a new payment method, then only the selected method (CreditCard or Check) needs to be bound and validated
It feels as if extending the DefaultModelBinder is the way to go, as I would like most of the heavy lifting to be done by the framework without the need to create a custom binder from scratch. However, when looking at the available methods to override, it's not clear which is the best one(s):
BindProperty - The problem here is that I basically need to look at one of the properties to determine what other properties should be bound. I don't think I can control the order in which the incoming properties are bound, and I wouldn't want to rely on the order they are set in the HTML form.
OnModelUpdated - By this point, it's too late. The binding validation from the data annotations has been triggered and the ModelState has been updated. I would have to loop through the ModelState and remove the errors that are not relevant.
OnPropertyValidating - At first I thought this is where I should look, but even returning TRUE for all properties (as a test) causes the ModelState to contain binding errors.
I have come across this scenario in other aspects of the application and decided to split up functionality into separate controller/actions to simplify the process. However, I would like to have a better understanding of how to approach more complex UI problems, particularly related to the MVC model binding features.
Any help on this subject would be greatly appreciated.
All the possible values are stored in a dropdown list. Using jQuery, I toggle the form (for a new payment method) and the display (for an existing method)
I have decided to try to circumvent model binding altogether and use FormCollection, IValueProvider, and TryUpdateModel inside my controller action.
Your issue sounds way to specialized to be placed in the default ModelBinder.
The ModelBinder is this seductress that lures you in on the pretense that she can solve all of your problems. But then you start merging ModelState's together and going off to do crazy things with nested objects lists and before you know it she slaps you with divorce papers and takes everything but your bones.
MVC 3 holds some promise to provide a more extensible ModelBinder but from my own personal experience unless its super simple what you need to change, such as empty texboxes becoming "" instead of null, than stay clear away from your own implementation.
The alternative approach is to use the existing ModelBinder functionality piecemeal and using things like Ignore method parameters to clean things up:
if( myModel.IsNewPayment )
UpdateModel( myModel.Payment, "exclude everything else" );
A lot of what your proposing to stuff into the model binder is really business logic too that should be in another layer. I've done some crazy things with my own ModelBinder and now regret every line of code I've written in there. Maybe its just me but your really bending the rules and completely trashing the "single responsibility principal" by putting business and payment logic in there.
Each time I start working on a new ASP.NET MVC web application, I'm not sure whether or not to use DataAnnotations validation. Something about it feels wrong.
For example, let's say I have a UserService which is passed a CreateUserModel from the Create action of the AccountController. To ensure the user always supplies a name, I set the model's Name property to have the [Required] attribute. I'm now safe in the knowledge that the model binder won't ever give me a CreateUserModel unless it has a name.
My problem is that for my UserService to be a reusable component of my system, it can't rely on the fact the layer above is supplying valid data, and surely must also validate this data. The need for this is highlighted further when you consider that you may want to write a web service that fully reuses the UserService (and wouldn't have the model binder to do all the data annotation validation for it).
So my question is: What is the best practice for this situation? Validate with data annotations and repeat that validation in the services? Validate only in the services and throw exceptions? A mix of both?
I hope my question isn't too subjective, I'm mainly trying to establish a consensus on whether moving the validation to data annotations is going to end up biting me in the end.
I perform all my validation in the service layer, using a combination of manual validations (if x == y) and using Data Annotations.
To use Data Annotations in your service layer, you have to manually use the Validator class using the TryValidateObject() method. A good example of this can be seen here.
You then have to pass your validation errors down from your service layer to your controller, and have your controller add each error to the Model state error list.
You are right, you should disable the validation on the controller and validate in the service layer. You can still use DataAnnotations if you want to. The service layer can throw an exception with the validation messages, the controller can catch that exception and add the validation messages to the ModelState. You can avoid doing that for each action by handling the validation exception on the OnException method of the controller.
I would personally don't mind that things are validated twice, as long as the logic is defined in one single place, which is clearly the case in your situation. I'm not experienced enough to say much about MVC, but I can imagine that throwing exceptions from the service layer just won't give a user experience (UX) that is as good as what MVC can give you when validating (it can for instance show an error message next to the textbox that is invalid. It is much harder to do that when throwing exceptions from your service layer). When the UX is the same, do your validation only in the service, otherwise do it in both layers.
When I started using xVal for client-side validation, I was only implementing action methods which used domain model objects as a viewmodel or embedded instances of those objects in the viewmodel.
This approach works fine most of the time, but there are cases when the view needs to display and post back only a subset of the model's properties (for example when the user wants to update his password, but not the rest of his profile data).
One (ugly) workaround is to have a hidden input field on the form for each property that is not otherwise present on the form.
Apparently the best practice here is to create a custom viewmodel which only contains properties relevant to the view and populate the viewmodel via Automapper. It's much cleaner since I am only transferring the data relevant to the view, but it's far from perfect since I have to repeat the same validation attributes that are already present on the domain model object.
Ideally I'd like to specify the Domain Model object as a meta class via a MetaData attribute (this is also often referred to as "buddy class"), but that doesn't work since xVal throws when the metadata class has properties that are not present on the viewmodel.
Is there any elegant workaround to this? I've been considering hacking the xVal sourcecode, but perhaps there is some other way I have overlooked so far.
Thanks,
Adrian
Edit: With the arrival of ASP.NET MVC 2, this is not only a problem related to validation attributes anymore, but it also applies to editor and display attributes.
This is the quintessential reason why your input screens should not be tightly coupled to your model. This question actually pops up here on the MVC tag about 3-4 times a month. I'd dupe if I could find the previous question and some of the comment discussion here is interesting. ;)
The issue your having is you're trying to force two different validation contexts of a model into a single model which fails under a large amount of scenarios. The best example is signing up a new user and then having an admin edit a user field later. You need to validate a password on a user object during registration but you won't show the password field to the admin editing the user details.
The choices for getting around these are all sub-optimal. I've worked on this problem for 3 projects now and implementing the following solutions has never been clean and usually frustrating. I'm going to try and be practical and forget all the DDD/db/model/hotnessofthemonth discussions everybody else is having.
1) Multiple View Models
Having viewmodels that are almost the same violates the DRY principal but I feel the costs of this approach are really low. Usually violating DRY amps up maintenance costs but IMHO the costs for this are the lowest and don't amount to much. Hypothetically speaking you don't change how max number characters the LastName field can have very often.
2) Dynamic Metadata
There are hooks in MVC 2 for providing your own metadata for a model. With this approach you could have whatever your using to provide metadata exclude certain fields based on the current HTTPRequest and therefore Action and Controller. I've used this technique to build a database driven permissions system which goes to the DB and tells the a subclass of the DataAnnotationsMetadataProvider to exclude properties based values stored in the database.
This technique is working great atm but the only problem is validating with UpdateModel(). To solve this problem we created a SmartUpdateModel() method which also goes to the database and automatically generates the exclude string[] array so that any non-permissisable fields aren't validated. We of course cached this for performance reasons so its not bad.
Just want to reiterate that we used [ValidationAttributes] on our models and then superceeded them with new rules on runtime. The end result was that the [Required] User.LastName field wasn't validated if the user didn't have permission to access it.
3) Crazy Interface Dynamic Proxy Thing
The last technique I tried to was to use interfaces for ViewModels. The end result was I had a User object that inherited from interfaces like IAdminEdit and IUserRegistration. IAdminEdit and IUserRegistration would both contain DataAnnotation attributes that performed all the context specific validation like a Password property with the interfaces.
This required some hackery and was more an academic exercise than anything else. The problem with 2 and 3 is that UpdateModel and the DataAnnotationsAttribute provider needed to be customized to be made aware of this technique.
My biggest stumbling block was I didn't ever want to send the whole user object to the view so I ended up using dynamic proxies to create runtime instances of IAdminEdit
Now I understand this is a very xVal specific question but all of the roads to dynamic validation like this lead to customization of the internal MVC Metadata providers. Since all the metadata stuff is new nothing is that clean or simple to do at this point. The work you'd have to do to customize MVC's validation behavior isn't hard but requires some in depth knowledge of how all of the internals work.
We moved our validation attributes to the ViewModel layer. In our case, this provided a cleaner separation of concerns anyway, as we were then able to design our domain model such that it couldn't get into an invalid state in the first place. For example, Date might be required on a BillingTransaction object. So we don't want to make it Nullable. But on our ViewModel, we might need to expose Nullable such that we can catch the situation where the user didn't enter a value.
In other cases, you might have validation that is specific per page/form, and you'll want to validate based on the command the user is trying to perform, rather than set a bunch of stuff and ask the domain model, "are you valid for trying to do XYZ", where in doing "ABC" those values are valid.
If ViewModels are hypothetically being forced upon you, then I recommend that they only enforce domain-agnostic requirements. This includes things like "username is required" and "email is formatted properly".
If you duplicate validation from the domain models in the view models, then you have tightly coupled the domain to the UI. When the domain validation changes ("can only apply 2 coupon per week" becomes "can only apply 1 coupon per week"), the UI must be updated. Generally speaking, this would be awful, and detrimental to agility.
If you move the validation from the domain models to the UI, you've essentially gutted your domain and placed the responsibility of validation on the UI. A second UI would have to duplicate all the validation, and you have coupled two separate UI's together. Now if the customer wants a special interface to administrate the inventory from their iPhone, the iPhone project needs to replicate all the validation that is also found in the website UI.
This would be even more awful than validation duplication described above.
Unless you can predict the future and can rule out these possibilities, only validate domain-agnostic requirements.
I don't know how this will play for client-side validation, but if partial validation is your issue you can modify the DataAnnotationsValidationRunner discussed here to take in an IEnumerable<string> list of property names, as follows:
public static class DataAnnotationsValidationRunner
{
public static IEnumerable<ErrorInfo> GetErrors(object instance, IEnumerable<string> fieldsToValidate)
{
return from prop in TypeDescriptor.GetProperties(instance).Cast<PropertyDescriptor>().Where(p => fieldsToValidate.Contains(p.Name))
from attribute in prop.Attributes.OfType<ValidationAttribute>()
where !attribute.IsValid(prop.GetValue(instance))
select new ErrorInfo(prop.Name, attribute.FormatErrorMessage(string.Empty), instance);
}
}
I'm gonna risk the downvotes and state that there is no benefit to ViewModels (in ASP.NET MVC), especially considering the overhead of creating and maintaining them. If the idea is to decouple from the domain, that is indefensible. A UI decoupled from a domain is not a UI for that domain. The UI must depend on the domain, so you're either going to have your Views/Actions coupled to the domain model, or your ViewModel management logic coupled to the domain model. The architecture argument is thus moot.
If the idea is to prevent users from hacking malicious HTTP POSTs that take advantage of ASP.NET MVC's model binding to mutate fields they shouldn't be allowed to change, then A) the domain should enforce this requirement, and B) the actions should provide whitelists of updateable properties to the model binder.
Unless you're domain is exposing something crazy like a live, in-memory object graph instead of entity copies, ViewModels are wasted effort. So to answer your question, keep domain validation in the domain model.
I understand annotating class properties with the basic required and minimum length and getting all the benefits of the asp.net mvc server side and client side validation.
However does anyone have a link that shows how you combine this 'base' validation with more complex business rules. How would I run business rule functions, such as for example, has the customer ordered anything in the last year (database hit required) and still use the same DataAnnotation and mvc validation plumbing?
Goal : Don't want two ways of generating and outputting validation methods.
From http://msdn.microsoft.com/en-us/library/dd901590%28VS.95%29.aspx:
To create customized validation checks, you can either create a class that derives from the ValidationAttribute class or create a method that performs the validation check and reference that method when applying the CustomValidationAttribute to the data member. When you create a class that derives from ValidationAttribute, override the IsValid method to provide the logic for your customized validation check.
There appears to be example code there.
Data Annotation run before your action is invoked. Then, regardless whether the validation succeded or not, the action is still called. If the DA detected invalid data, your ModelState will be invalid.
Once here, you can still do any validation you want, for your business rules, as you would normally do without the data annotation, if you want to. In your action, you can add errors to the ModelState even if the Data Annotation validation passed.
In this case, you add your errors with ModelState.addError, and those errors are added to any error provided by the DA. So in your View it doesn't matter where the error comes from.
Or, if your rules are general, you can write your own annotation tags. The Data Annotation thing is distributed with its source, so you have full control on it.
You could use VAB (Application Validation Block) from the Enterprise Library 5 of Microsoft that actually based on the DataAnnotations class but u do your complex bussiness logic very easily through configuration...
i'd suggest you check it out...
Have a look at following article, where you can use DataAnnotations Multiple Times On Same Field, Compare N number of properties and N number of values....
http://www.codeproject.com/KB/validation/MultipleDataAnnotations.aspx