Develop Reference

"Complex validation" with INotifyDataErrorInfo and MVVM (MVVMLight)

Basically the problem is that I want to perform validation against some values that I get form a database (EF) before I execute the BL. I'm currently using INotifyDataErrorInfo with attributes in the properties of my ViewModel. I tried to do this validation with a custom validator (CustomValidation attribute):
private string unit;
[Required(AllowEmptyStrings = false, ErrorMessage = Constants.Error6)]
[RegularExpression(Constants.AlphabeticRegEx, ErrorMessage = Constants.Error10)]
[CustomValidation(typeof(ProductSelectionViewModel),"IsInRegisteredUnits")]
public string Unit
{
get { return unit; }
set
{
if (value == unit)
return;
unit = value;
RaisePropertyChanged(vm => vm.Unit);
UpdateUnitPrice(selectedProduct, unit);
}
}
But the method in charge of performing this validation must be a static one, so under this scenario I cannot acces to my repository since it is not static.
public static ValidationResult IsInRegisteredUnits(object obj, ValidationContext context)
{
var productSelectionViewModel = (ProductSelectionViewModel)context.ObjectInstance;
if (!unitService.GetAllUnitsAbbreviation().Any(x=>x.Equals(productSelectionViewModel.Unit, StringComparison.CurrentCultureIgnoreCase)))
return new ValidationResult("La unidad ingresada no es válida", new List<string> { "Unit" });
return ValidationResult.Success;
}
How can I solve this (unitService.GetAllUnitsAbbreviation() cannot be a static method since its using a repository), maybe I'm performing this kind of validation in the worng place (wrong design), any help would be appreciated :)

Custom Dataannotations, Client side Validation, ViewModels, & Model State

This is an extension of an older question from this post:
Enforcing a model's boolean value to be true using data annotations
This gave me a lot of insight on how to get the client side custom validation working with jquery-unubtrusive-ajax.js.
Here is the answer code:
namespace Checked.Entitites
{
public class BooleanRequiredAttribute : ValidationAttribute, IClientValidatable
{
public override bool IsValid(object value)
{
return value != null && (bool)value == true;
}
public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
{
//return new ModelClientValidationRule[] { new ModelClientValidationRule() { ValidationType = "booleanrequired", ErrorMessage = this.ErrorMessage } };
yield return new ModelClientValidationRule()
{
ValidationType = "booleanrequired",
ErrorMessage = this.ErrorMessageString
};
}
}
}
When i use this custom attribute in my models it works fine.
ex:
[BooleanRequired(ErrorMessage = "Please accept the terms")]
public bool Terms { get; set; }
When i use textboxfor in my views the error messages populate in the html validation summary.
#Html.CheckBoxFor(model => model.Terms, new { #class = "legalbox", #placeholder = "Terms" })
I also had to add this line to my jquery.unubtrusive-ajax.js
$.validator.unobtrusive.adapters.addBool("BooleanRequired", "required");
The issue i am having with this fix arises when i reference this model in the controller and check the modelstate. The modelstate is always false no matter what i have as the value for this custom validated field. It looks like the override isvalid is working in the client side validation but not on the server side. I need it to work on both and have been scouring trying to find a solution that isn't "ditch dataannotations and use something else".
The specific line i am using in my controller that will never pass with this field is as follows:
if (ModelState.IsValid) {
//Logic here
}
The rest of the model using the standard data-annotations validate correctly, i just cannot get this custom one to work the same way as the built in attributes. Its possible that the right solution would prevent me from having to add that line to the unobtrusive ajax file.
Any help would be appreciated.
Thanks

Get error message when using custom validation attribute

I'm using the CustomValidationAttribute like this
[CustomValidation(typeof(MyValidator),"Validate",ErrorMessage = "Foo")]
And my validator contains this code
public class MyValidator {
public static ValidationResult Validate(TestProperty testProperty, ValidationContext validationContext) {
if (string.IsNullOrEmpty(testProperty.Name)) {
return new ValidationResult(""); <-- how can I get the error message from the custom validation attribute?
}
return ValidationResult.Success;
}
}
So how can I get the error message from the custom validation attribute?

I know this is a little of an old post, but I will provide an better answer to the question.
The asker wants to use the CustomValidationAttribute and pass in an error message using the ErrorMessage property.
If you would like your static method to use the error message that you provided when decorating your property, then you return either:
new ValidationResult(string.Empty) or ValidationResult("") or ValidationResult(null).
The CustomValidationAttribute overrides the FormatErrorMessage of its base class and does a conditional check for string.IsNullOrEmpty.

There's no reliable way to get the error message from the attribute. Alternatively you could write a custom validation attribute:
[MyValidator(ErrorMessage = "Foo")]
public TestProperty SomeProperty { get; set; }
like this:
public class MyValidatorAttribute : ValidationAttribute
{
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
var testProperty = (TestProperty)value;
if (testProperty == null || string.IsNullOrEmpty(testProperty.Name))
{
return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
}
return null;
}
}
In this case the error message will be inferred from the custom validation attribute.

You can look into the following posting to get some ideas on how to do what you want to do (they use JS):
Custom validator error text through javascript?
Hope this helps.

The only way I have found that works is to validate the model from the post back method using TryValidateObject and if it fails, show the model again - then the error will show up.
[HttpPost]
public ActionResult Standard(Standard model)
{
var valContext = new ValidationContext(model, null, null);
var valResults = new List<ValidationResult>();;
bool b = Validator.TryValidateObject(model, valContext, valResults, true);
if(!b)
return View(model);
...

Recursive validation using annotations and IValidatableObject

I am trying to validate nested objects (not models in the MVC senss) using annotations and some custom code.
I found the following post useful
Using Data Annotations Validation Manually and Object Graphs
As suggested in an answer, I've created an extra routine in the container class to validate the nested object. Here's my modified test code
public class Customer : IValidatableObject
{
public Customer()
{
Details = new CustomerDetails();
}
[Required]
[MaxLength(2)]
public string Name
{
get;
set;
}
public CustomerDetails Details
{
get;
private set;
}
public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
var context = new ValidationContext(this.Details, validationContext.ServiceContainer, validationContext.Items);
var results = new List<ValidationResult>();
Validator.TryValidateObject(this.Details, context, results);
return results;
}
}
However I have problems getting all the validation errors, even when calling TryValidateObject with validateAllProperties set to true.
var context = new ValidationContext(cs, null, null);
var results = new List<ValidationResult>();
Validator.TryValidateObject(cs, context, results,true);
If there are any errors in the container, only these will show. Only when there are no errors in the container object, errors in the nested object will show. I suspect it has something to do with the Validate rouine returning a full list, and not being able to add to an (existing) list from the container(?)
Are there any modifications I can make to routine to get all errors to show?

See this answer: https://stackoverflow.com/a/3400627/724944
So, there is an error in your class' atributes, and therefore Validate method doesn't get called.
I suggest using CustomValidationAttribute like this:
[CustomValidation(typeof(Customer), "ValidateRelatedObject")]
public CustomerDetails Details
{
get;
private set;
}
public static ValidationResult ValidateRelatedObject(object value, ValidationContext context)
{
var context = new ValidationContext(value, validationContext.ServiceContainer, validationContext.Items);
var results = new List<ValidationResult>();
Validator.TryValidateObject(value, context, results);
// TODO: Wrap or parse multiple ValidationResult's into one ValidationResult
return result;
}

Validation of Guid

I have a strongly-typed view which has a DropDownListFor attribute on it.
Each item in the dropdown list is represented by a GUID.
What I'm after is a way to validate if a user selects an item from the dropdown list. At present i don't see anyway of doing this using Data Annotations.
Is there anyway of achieving this using Data Annotations so client and server side validation would work.
I'm guessing i need to make a custom method to do this but was wondering if anything already existed.

Actually, you can't use Required attribute with GUIDs (without the method I mention below) because they inherit from struct, and as such their default value is actually an instance of Guid.Empty, which will satisfy the requirements of the Required attribute. Now that being said, it is possible to get what you want you just need to make your property nullable, take this for example...
public class Person
{
[Required] //Only works because the Guid is nullable
public Guid? PersonId { get; set;}
public string FirstName { get; set;}
public string LastName { get; set;}
}
By marking the GUID nullable (using the ?, or Nullable if you prefer the long way) you let it stay as null when binding against what the browser sent. In your case, just make sure the value of the default option of the dropdown uses an empty string as it's value.
EDIT: The only caveat to this method is you end up having to use something like Person.GetValueOfDefault() everywhere and potentially testing for Guid.Empty. I got tired of doing this and ended up creating my own validation attribute to help simplify validating Guids (and any other types that have default values I want to treat as invalid such as int, DateTime, etc). However I don't have client side validation to go along with this yet, so validation only happens on the server. This can be combined with [Required] (designed to not duplicate functionality of [Required]) if you're ok with using nullable types. This would mean you still have to use GetValueOrDefault(), but at least then you don't have to test for Guid.Empty anymore. The Gist link has some XMLDocs with examples, I left them out here for brevity. I'm currently using it with ASP.NET Core.
EDIT: Updated to fix a bug with Nullable<>, and a bug with treating null as invalid. Added supporting classes to handle client side validation. See Gist for full code.
Gist: RequireNonDefaultAttribute
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false)]
public class RequireNonDefaultAttribute : ValidationAttribute
{
public RequireNonDefaultAttribute()
: base("The {0} field requires a non-default value.")
{
}
public override bool IsValid(object value)
{
if (value is null)
return true; //You can flip this if you want. I wanted leave the responsability of null to RequiredAttribute
var type = value.GetType();
return !Equals(value, Activator.CreateInstance(Nullable.GetUnderlyingType(type) ?? type));
}
}

Edited Answer
Upon re-reading your question, it sounds like you just want to know if a value is selected. If that's the case then just apply the RequiredAttribute to the Guid property and make it nullable on the model
public class GuidModel
{
[Required]
public Guid? Guid { get; set; }
public IEnumerable<Guid> Guids { get; set; }
}
then in the strongly typed View (with #model GuidModel)
#Html.ValidationMessageFor(m => m.Guid)
#Html.DropDownListFor(
m => m.Guid,
Model.Guids.Select(g => new SelectListItem {Text = g.ToString(), Value = g.ToString()}),
"-- Select Guid --")
Add the client validation JavaScript script references for client-side validation.
The controller looks like
public class GuidsController : Controller
{
public GuidRepository GuidRepo { get; private set; }
public GuidsController(GuidRepository guidRepo)
{
GuidRepo = guidRepo;
}
[HttpGet]
public ActionResult Edit(int id)
{
var guid = GuidRepo.GetForId(id);
var guids - GuidRepo.All();
return View(new GuidModel { Guid = guid, Guids = guids });
}
[HttpPost]
public ActionResult Edit(GuidModel model)
{
if (!ModelState.IsValid)
{
model.Guids = GuidRepo.All();
return View(model);
}
/* update db */
return RedirectToAction("Edit");
}
}
This will ensure that the Guid property is required for a model-bound GuidModel.
Original Answer
I don't believe that there is a ready made Data Annotation Validation attribute that is capable of doing this. I wrote a blog post about one way to achieve this; the post is using an IoC container but you could take the hard coded dependency if you're wanting to get something working.
Something like
public class ValidGuidAttribute : ValidationAttribute
{
private const string DefaultErrorMessage = "'{0}' does not contain a valid guid";
public ValidGuidAttribute() : base(DefaultErrorMessage)
{
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
var input = Convert.ToString(value, CultureInfo.CurrentCulture);
// let the Required attribute take care of this validation
if (string.IsNullOrWhiteSpace(input))
{
return null;
}
// get all of your guids (assume a repo is being used)
var guids = new GuidRepository().AllGuids();
Guid guid;
if (!Guid.TryParse(input, out guid))
{
// not a validstring representation of a guid
return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
}
// is the passed guid one we know about?
return guids.Any(g => g == guid) ?
new ValidationResult(FormatErrorMessage(validationContext.DisplayName)) : null;
}
}
and then on the model you send into the controller action
public class GuidModel
{
[ValidGuid]
public Guid guid { get; set; }
}
This gives you server side validation. You could write client side validation to do this as well, perhaps using RemoteAttribute but I don't see a lot of value in this case as the only people that are going to see this client side validation are people that are messing with values in the DOM; it would be of no benefit to your normal user.

I know this is an old question now, but if anyone else is interested I managed to get around this by creating an [IsNotEmpty] annotation (making the Guid nullable wasn't an option in my case).
This uses reflection to work out whether there's an implementation of Empty on the property, and if so compares it.
public class IsNotEmptyAttribute : ValidationAttribute
{
public override bool IsValid(object value)
{
if (value == null) return false;
var valueType = value.GetType();
var emptyField = valueType.GetField("Empty");
if (emptyField == null) return true;
var emptyValue = emptyField.GetValue(null);
return !value.Equals(emptyValue);
}
}

Regex actually does work (if you use the right one!)
[Required]
[RegularExpression("^((?!00000000-0000-0000-0000-000000000000).)*$", ErrorMessage = "Cannot use default Guid")]
public Guid Id { get; set; }

Non Empty Guid Validator
prevents 00000000-0000-0000-0000-000000000000
Attribute:
using System.ComponentModel.DataAnnotations;
[AttributeUsage(AttributeTargets.Property)]
internal class NonEmptyGuidAttribute : ValidationAttribute
{
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
if ((value is Guid) && Guid.Empty == (Guid)value)
{
return new ValidationResult("Guid cannot be empty.");
}
return null;
}
}
Model:
using System.ComponentModel.DataAnnotations;
public class Material
{
[Required]
[NonEmptyGuid]
public Guid Guid { get; set; }
}

If the custom validation doesn't require a high reuse in your system (i.e. without the need for a custom validation attribute), there's another way to add custom validation to a ViewModel / Posted data model, viz by using IValidatableObject.
Each error can be bound to one or more model properties, so this approach still works with e.g. Unobtrusive validation in MVC Razor.
Here's how to check a Guid for default (C# 7.1):
public class MyModel : IValidatableObject // Implement IValidatableObject
{
[Required]
public string Name {get; set;}
public Guid SomeGuid {get; set;}
... other properties here
public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
if (SomeGuid == default)
{
yield return new ValidationResult(
"SomeGuid must be provided",
new[] { nameof(SomeGuid) });
}
}
}
More on IValidatableObject here

You can validate the Guid if it contains default values - "00000000-0000-0000-0000-000000000000".
if (model.Id == Guid.Empty)
{
// TODO: handle the error or do something else
}

You can create a custom validator for that.
using System;
using System.ComponentModel.DataAnnotations;
namespace {{Your_App_Name}}.Pages
{
public class NotEmptyGuidAttribute: ValidationAttribute
{
protected override ValidationResult IsValid(object guidValue, ValidationContext validationContext)
{
var emptyGuid = new Guid();
var guid = new Guid(guidValue.ToString());
if (guid != emptyGuid){
return null;
}
return new ValidationResult(ErrorMessage, new[] {validationContext.MemberName});
}
}
}
You can use it like this
[EmptyGuidValidator(ErrorMessage = "Role is required.")]
public Guid MyGuid{ get; set; }
This worked for me.