I have the following situation - I need to write a custom additional metadata attribute, that based on another property value (from the same model), adds a value to the AdditionalValues dictionary. Right now, my issue is that I'm not able to access the model instance inside my attribute class.
[AttributeUsage(AttributeTargets.Property)]
public class ExtendedAdditionalMetadataAttribute : Attribute, IMetadataAware
{
#region Private properties
private string extraFieldToCheck { get; set; }
private string extraFieldValueToCheck { get; set; }
private string fieldToBeAdded { get; set; }
private string fieldValueToBeAdded { get; set; }
#endregion
#region Constructor
public ExtendedAdditionalMetadataAttribute(string extraFieldToCheck, string extraFieldValueToCheck,
string fieldToBeAdded, string fieldValueToBeAdded)
{
this.extraFieldToCheck = extraFieldToCheck;
this.extraFieldValueToCheck = extraFieldValueToCheck;
this.fieldToBeAdded = fieldToBeAdded;
this.fieldValueToBeAdded = fieldValueToBeAdded;
}
#endregion
public void OnMetadataCreated(ModelMetadata metadata)
{
// HOW TO GET THE MODEL CLASS INSTANCE???
// metadata.ContainerType is correct by metadata.Container is null.
}
}
As you see from the code comments, inside OnMetadataCreated I need to access the Model class instance but, though ContainerType is correct, the Container property is NULL.
Can you please help me by giving me a hint regarding this issue?
THANK YOU IN ADVANCE!
Evdin
LATER EDIT
Considering that I haven't gave to much explanations, I will also paste here an example on how I would like to use this attribute on a model class:
/// <summary>
/// Gets or sets the IsAccountCreated
/// </summary>
/// <value>The IsAccountCreated.</value>
[UIHint("FormFieldStringTemplate")]
[ExtendedAdditionalMetadata("IsExternalAccount", "true", "ReadOnly", "true")]
public override Boolean IsAccountCreated { get; set; }
/// <summary>
/// Gets or sets the IsAccountEnabled
/// </summary>
/// <value>The IsAccountEnabled.</value>
[Display(Name = "Este cont activ?")]
[UIHint("FormFieldStringTemplate")]
[ExtendedAdditionalMetadata("IsExternalAccount", "true", "ReadOnly", "true")]
public override Boolean IsAccountEnabled { get; set; }
/// <summary>
/// Gets or sets the IsExternalAccount
/// </summary>
/// <value>The IsExternalAccount.</value>
[Display(Name = "Este cont extern?")]
[UIHint("FormFieldStringTemplate")]
[AdditionalMetadata("ReadOnly", "true")]
public override Boolean IsExternalAccount { get; set; }
Later & Later Edit
Though the response given by #stephen-muecke is more then simple and acceptable in current situation, for the sake of programming challenge I've looked for other options and I found the following possibility: implementing a custom DataAnnotationsModelMetadataProvider class. In few simple words - it works and I'm able to obtain the model class instance BUT only if the model class is a simple class, otherwise there are many drawbacks - for example if you have a Model class and you use it in your view then it's ok but if you have a class inside another class (a model inside a viewmodel) that this approach is not usable anymore.
Thank you again #stephen-muecke!
Since you seem to need access to multiple properties of the model, the attribute should target class (AttributeTargets.Class) and be applied to the model, not a property. This might mean you need to add another property that is the name of the property you were trying to apply this to. Note metadata.ContainerType only gives you the type, not this instance so you can only get the default value of its properties.
Edit
If the attributes need to be applied to multiple properties in the model, then you cannot access the container in OnMetadataCreated because metadata is created from the innermost properties out so the model's metadata has not yet been created.
Based on OP's comments, a better solution would be to create a custom html helper. For example to generate a textbox that is readonly based on the value of another property
namespace MyHelpers.Html
{
public static class ReadOnlyHelpers
{
public static MvcHtmlString ReadOnlyTextBoxIf<TModel, TValue>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TValue>> expression, bool isReadOnly)
{
object attributes = isReadOnly ? new { #readonly = "readonly" } : null;
return InputExtensions.TextBoxFor(helper, expression, attributes);
}
}
}
and use in your view as
#Html.ReadOnlyTextBoxIf(m => m.SomeTextProperty, Model.SomeBooleanValue)
Creating a 'Readonly' checkbox is a little more difficult because the readonly attribute has no affect with a checkbox. In order to prevent user interaction you need to disable it but that means the value wont post back
public static MvcHtmlString ReadOnlyCheckBoxIf<TModel>(this HtmlHelper<TModel> helper, Expression<Func<TModel, bool>> expression, bool isReadOnly)
{
if (isReadOnly)
{
// If you want to 'visually' render a checkbox (otherwise just render a div with "YES" or "NO")
ModelMetadata metaData = ModelMetadata.FromLambdaExpression(expression, helper.ViewData);
StringBuilder html = new StringBuilder();
// Add a hidden input for postback
html.Append(InputExtensions.HiddenFor(helper, expression).ToString());
// Add a visual checkbox without name so it does not post back
TagBuilder checkbox = new TagBuilder("input");
checkbox.MergeAttribute("type", "checkbox");
checkbox.MergeAttribute("disabled", "disabled");
if ((bool)metaData.Model)
{
checkbox.MergeAttribute("checked", "checked");
}
html.Append(checkbox.ToString());
return MvcHtmlString.Create(html.ToString());
}
else
{
// return normal checkbox
return InputExtensions.CheckBoxFor(helper, expression);
}
}
and use in your view as
#Html.ReadOnlyCheckBoxIf(m => m.IsAccountCreated, Model.IsExternalAccount)
Related
I can always go and do what is mentioned here. Using Enum.TryParse
However What I am doing is passing a string to the request. Then created a local variable on my controller of the Enum type so that I can pass the Enum type to my service method to perform task. I feel like if I can directly convert it to the type of Enum on the request's set property, that would be great.
This is what I have currently:
public enum SearchSortType
{
None,
Rating,
Date,
Etc
}
[DataContract]
public class MyRequest
{
/// <summary>
/// The field to order on.
/// </summary>
/// <value>
/// The order by.
/// </value>
[DataMember(Name = "sortOn")]
public string SortOn { get; set; }
}
what I want is following. I will keep posting String from the request.
[DataContract]
public class MyRequest
{
/// <summary>
/// The field to order on.
/// </summary>
/// <value>
/// The order by.
/// </value>
[DataMember(Name = "sortOn")]
public SearchSortType SortOn { get; set; }
}
Is it possible to keep passing string and get it converted on the set property ( or any other way to the enum so that I don't have to create a local variable and convert and then use it?
You can write your own model binder that will accept string.
public class EnumModelBinder : DefaultModelBinder
{
/// <summary>
/// Fix for the default model binder's failure to decode enum types when binding to JSON.
/// </summary>
protected override object GetPropertyValue(ControllerContext controllerContext, ModelBindingContext bindingContext,
PropertyDescriptor propertyDescriptor, IModelBinder propertyBinder)
{
var propertyType = propertyDescriptor.PropertyType;
if (propertyType.IsEnum)
{
var providerValue = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
if (null != providerValue)
{
var value = providerValue.RawValue;
if (null != value)
{
var valueType = value.GetType();
if (!valueType.IsEnum)
{
return Enum.ToObject(propertyType, value);
}
}
}
}
return base.GetPropertyValue(controllerContext, bindingContext, propertyDescriptor, propertyBinder);
}
}
Then simply register it in your Global.asax file.
protected override void OnApplicationStarted()
{
base.OnApplicationStarted();
AreaRegistration.RegisterAllAreas();
RegisterRoutes(RouteTable.Routes);
// Register your new model binder
ModelBinders.Binders.DefaultBinder = new EnumModelBinder();
}
Enum is a distinct type that consists of a set of named constants called the enumerator list. You can pass the enum in the request and have an enum property on the web api with the same name and .net model binder will automatically bind it to the enum. When the enum is sent in the request it will be send as an Int.
Can anyone please explain to me a very basic example of a custom attribute with code?
You start by writing a class that derives from Attribute:
public class MyCustomAttribute: Attribute
{
public string SomeProperty { get; set; }
}
Then you could decorate anything (class, method, property, ...) with this attribute:
[MyCustomAttribute(SomeProperty = "foo bar")]
public class Foo
{
}
and finally you would use reflection to fetch it:
var customAttributes = (MyCustomAttribute[])typeof(Foo).GetCustomAttributes(typeof(MyCustomAttribute), true);
if (customAttributes.Length > 0)
{
var myAttribute = customAttributes[0];
string value = myAttribute.SomeProperty;
// TODO: Do something with the value
}
You could limit the target types to which this custom attribute could be applied using the AttributeUsage attribute:
/// <summary>
/// This attribute can only be applied to classes
/// </summary>
[AttributeUsage(AttributeTargets.Class)]
public class MyCustomAttribute : Attribute
Important things to know about attributes:
Attributes are metadata.
They are baked into the assembly at compile-time which has very serious implications of how you could set their properties. Only constant (known at compile time) values are accepted
The only way to make any sense and usage of custom attributes is to use Reflection. So if you don't use reflection at runtime to fetch them and decorate something with a custom attribute don't expect much to happen.
The time of creation of the attributes is non-deterministic. They are instantiated by the CLR and you have absolutely no control over it.
While the code to create a custom Attribute is fairly simple, it's very important that you understand what attributes are:
Attributes are metadata compiled into your program. Attributes themselves do not add any functionality to a class, property or module - just data. However, using reflection, one can leverage those attributes in order to create functionality.
So, for instance, let's look at the Validation Application Block, from Microsoft's Enterprise Library. If you look at a code example, you'll see:
/// <summary>
/// blah blah code.
/// </summary>
[DataMember]
[StringLengthValidator(8, RangeBoundaryType.Inclusive, 8, RangeBoundaryType.Inclusive, MessageTemplate = "\"{1}\" must always have \"{4}\" characters.")]
public string Code { get; set; }
From the snippet above, one might guess that the code will always be validated, whenever changed, accordingly to the rules of the Validator (in the example, have at least 8 characters and at most 8 characters). But the truth is that the Attribute does nothing; as mentioned previously, it only adds metadata to the property.
However, the Enterprise Library has a Validation.Validate method that will look into your object, and for each property, it'll check if the contents violate the rule informed by the attribute.
So, that's how you should think about attributes -- a way to add data to your code that might be later used by other methods/classes/etc.
Utilizing/Copying Darin Dimitrov's great response, this is how to access a custom attribute on a property and not a class:
The decorated property [of class Foo]:
[MyCustomAttribute(SomeProperty = "This is a custom property")]
public string MyProperty { get; set; }
Fetching it:
PropertyInfo propertyInfo = typeof(Foo).GetProperty(propertyToCheck);
object[] attribute = propertyInfo.GetCustomAttributes(typeof(MyCustomAttribute), true);
if (attribute.Length > 0)
{
MyCustomAttribute myAttribute = (MyCustomAttribute)attribute[0];
string propertyValue = myAttribute.SomeProperty;
}
You can throw this in a loop and use reflection to access this custom attribute on each property of class Foo, as well:
foreach (PropertyInfo propertyInfo in Foo.GetType().GetProperties())
{
string propertyName = propertyInfo.Name;
object[] attribute = propertyInfo.GetCustomAttributes(typeof(MyCustomAttribute), true);
// Just in case you have a property without this annotation
if (attribute.Length > 0)
{
MyCustomAttribute myAttribute = (MyCustomAttribute)attribute[0];
string propertyValue = myAttribute.SomeProperty;
// TODO: whatever you need with this propertyValue
}
}
Major thanks to you, Darin!!
The short answer is for creating an attribute in c# you only need to inherit it from Attribute class, Just this :)
But here I'm going to explain attributes in detail:
basically attributes are classes that we can use them for applying our logic to assemblies, classes, methods, properties, fields, ...
In .Net, Microsoft has provided some predefined Attributes like Obsolete or Validation Attributes like ( [Required], [StringLength(100)], [Range(0, 999.99)]), also we have kind of attributes like ActionFilters in asp.net that can be very useful for applying our desired logic to our codes (read this article about action filters if you are passionate to learn it)
one another point, you can apply a kind of configuration on your attribute via AttibuteUsage.
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct, AllowMultiple = true)]
When you decorate an attribute class with AttributeUsage you can tell to c# compiler where I'm going to use this attribute: I'm going to use this on classes, on assemblies on properties or on ... and my attribute is allowed to use several times on defined targets(classes, assemblies, properties,...) or not?!
After this definition about attributes I'm going to show you an example:
Imagine we want to define a new lesson in university and we want to allow just admins and masters in our university to define a new Lesson, Ok?
namespace ConsoleApp1
{
/// <summary>
/// All Roles in our scenario
/// </summary>
public enum UniversityRoles
{
Admin,
Master,
Employee,
Student
}
/// <summary>
/// This attribute will check the Max Length of Properties/fields
/// </summary>
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct, AllowMultiple = true)]
public class ValidRoleForAccess : Attribute
{
public ValidRoleForAccess(UniversityRoles role)
{
Role = role;
}
public UniversityRoles Role { get; private set; }
}
/// <summary>
/// we suppose that just admins and masters can define new Lesson
/// </summary>
[ValidRoleForAccess(UniversityRoles.Admin)]
[ValidRoleForAccess(UniversityRoles.Master)]
public class Lesson
{
public Lesson(int id, string name, DateTime startTime, User owner)
{
var lessType = typeof(Lesson);
var validRolesForAccesses = lessType.GetCustomAttributes<ValidRoleForAccess>();
if (validRolesForAccesses.All(x => x.Role.ToString() != owner.GetType().Name))
{
throw new Exception("You are not Allowed to define a new lesson");
}
Id = id;
Name = name;
StartTime = startTime;
Owner = owner;
}
public int Id { get; private set; }
public string Name { get; private set; }
public DateTime StartTime { get; private set; }
/// <summary>
/// Owner is some one who define the lesson in university website
/// </summary>
public User Owner { get; private set; }
}
public abstract class User
{
public int Id { get; set; }
public string Name { get; set; }
public DateTime DateOfBirth { get; set; }
}
public class Master : User
{
public DateTime HireDate { get; set; }
public Decimal Salary { get; set; }
public string Department { get; set; }
}
public class Student : User
{
public float GPA { get; set; }
}
class Program
{
static void Main(string[] args)
{
#region exampl1
var master = new Master()
{
Name = "Hamid Hasani",
Id = 1,
DateOfBirth = new DateTime(1994, 8, 15),
Department = "Computer Engineering",
HireDate = new DateTime(2018, 1, 1),
Salary = 10000
};
var math = new Lesson(1, "Math", DateTime.Today, master);
#endregion
#region exampl2
var student = new Student()
{
Name = "Hamid Hasani",
Id = 1,
DateOfBirth = new DateTime(1994, 8, 15),
GPA = 16
};
var literature = new Lesson(2, "literature", DateTime.Now.AddDays(7), student);
#endregion
ReadLine();
}
}
}
In the real world of programming maybe we don't use this approach for using attributes and I said this because of its educational point in using attributes
I have the following ExportMetaData attributes set on my class:
[Export(typeof(IDocumentViewer))]
[ExportMetadata("Name", "MyViewer")]
[ExportMetadata("SupportsEditing", true)]
[ExportMetadata("Formats", DocFormat.DOC, IsMultiple = true)]
[ExportMetadata("Formats", DocFormat.DOCX, IsMultiple = true)]
[ExportMetadata("Formats", DocFormat.RTF, IsMultiple = true)]
I also have a supporting interface:
public interface IDocumentViewerMetaData {
/// <summary>
/// Gets the format.
/// </summary>
/// <value>The format.</value>
IEnumerable<DocFormat> Formats { get; }
/// <summary>
/// Gets the name of the viewer
/// </summary>
/// <value>The name.</value>
string Name { get; }
/// <summary>
/// Gets a value indicating whether this viewer supports editing
/// </summary>
/// <value><c>true</c> if [supports editing]; otherwise, <c>false</c>.</value>
bool SupportsEditing { get; }
}
And of course my ImportMany:
[ImportMany(typeof(IDocumentViewer))]
public IEnumerable<Lazy<IDocumentViewer, IDocumentViewerMetaData>> _viewers { get; set; }
What I would like to do is use a strongly-typed attribute class instead of using the ExportMetaData attribute. I have not figured out a way to do this while also supporting single values (Name, SupportsEditing, in the example above).
I envision doing something similiar the following (or whatever is suggested as best):
[Export(typeof(IDocumentViewer))]
[DocumentViewerMetadata(Name = "MyViewer")]
[DocumentViewerMetadata(SupportsEditing = true)]
[DocumentViewerMetadata(Format = DocFormat.DOC)]
[DocumentViewerMetadata(Format = DocFormat.DOCX)]
I am fairly certain that there IS a way to do this, I just haven't found the right way to connect the dots. :)
You can subclass the ExportAttribute with your own implementation, and decorate it with a MetadataAttribute to allow MEF to use its properties to project the metadata proxy it uses during composition:
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Property),
MetadataAttribute]
public class ExportDocumentViewerAttribute : ExportAttribute, IDocumentViewerMetadata
{
public ExportDocumentViewer(string name, bool supportsEditing, params DocFormat[] formats)
: base(typeof(IDocumentViewer))
{
if (string.IsNullOrEmpty(name))
throw new ArgumentException("Export requires a name", "name");
Name = name;
SupportsEditing = supportsEditing;
Formats = formats ?? Enumerable.Empty<DocFormat>();
}
public string Name { get; private set; }
public bool SupportsEditing { get; private set; }
public IEnumerable<DocFormat> Formats { get; private set; }
}
[ExportDocumentViewer("Word", true, DocFormat.DOC, DocFormat.DOCX)]
public WordDocumentViewer : IDocumentViewer
{
// Stuff
}
Note you don't actually need to decorate it with your IDocumentViewerMetadata contract, as MEF will project it regardless, I just prefer to so that I know if I make changes to the metadata contract, that my custom export attribute conforms.
I've been using the MetadataType attribute to add validation attributes to classes I'm generating using a T4 template. This works wonderfully, but I'd like to be able to use the DefaultValue attribute on some properties, so that my MetadataType class will more completely describe my classes (and so that I won't have to implement the OnCreated method in those classes). I can add the attribute to my MetadataType class, but it has no effect.
Here is some example source - the generated part is (of course) in a different file. If I instantiate a Widget object, the Name property will be null.
/// <summary>
/// This part is generated
/// </summary>
public partial class Widget
{
public string Name { get; set; }
}
/// <summary>
/// This part is hand-coded so I can add attributes, custom methods etc.
/// </summary>
[System.ComponentModel.DataAnnotations.MetadataType(typeof(WidgetMetadata))]
public partial class Widget
{
}
/// <summary>
/// This part is hand-coded, and any validation attributes I add work fine.
/// </summary>
public class WidgetMetadata
{
[System.ComponentModel.DefaultValue("Default Name")]
[StringLengthValidator(0, RangeBoundaryType.Inclusive, 320, RangeBoundaryType.Inclusive, Tag = "Invalid string length", MessageTemplate = "{1} must contain between \'{3}\' to \'{5}\' characters.")]
public string Name { get; set; }
}
What am I doing wrong?, or is this not supported (and if so is it documented anywhere?)
Add a constructor to the WidgetMetaData class and set the default value of the property there. The DefaultValueAttribute is used for the Visual Studio Toolbox (I believe) to determine whether the value should be bold (changed) or not (default value), among other things. You still need to set the value of the property at some point.
public WidgetMetaData()
{
Name = "Default Value";
}
More information on the DefaultValueAttribute: http://msdn.microsoft.com/en-us/library/system.componentmodel.defaultvalueattribute(v=vs.71).aspx
Can I automatically validate complex child objects when validating a parent object and include the results in the populated ICollection<ValidationResult>?
If I run the following code:
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
namespace ConsoleApplication1
{
public class Person
{
[Required]
public string Name { get; set; }
public Address Address { get; set; }
}
public class Address
{
[Required]
public string Street { get; set; }
[Required]
public string City { get; set; }
[Required]
public string State { get; set; }
}
class Program
{
static void Main(string[] args)
{
Person person = new Person
{
Name = null,
Address = new Address
{
Street = "123 Any St",
City = "New York",
State = null
}
};
var validationContext = new ValidationContext(person, null, null);
var validationResults = new List<ValidationResult>();
var isValid = Validator.TryValidateObject(person, validationContext, validationResults);
Console.WriteLine(isValid);
validationResults.ForEach(r => Console.WriteLine(r.ErrorMessage));
Console.ReadKey(true);
}
}
}
I get the following output:
False
The Name field is required.
But I was expecting something similar to:
False
The Name field is required.
The State field is required.
I offered a bounty for a better child object validation solution but didn't get any takers, ideally
validating child objects to an arbitrary depth
handling multiple errors per object
correctly identifying the validation errors on the child object fields.
I'm still surprised the framework doesn't support this.
Issue - Model Binder Order
This is, unfortunately, the standard behavior of Validator.TryValidateObject which
does not recursively validate the property values of the object
As pointed out in Jeff Handley's article on Validating Object and Properties with the Validator, by default, the validator will validate in order:
Property-Level Attributes
Object-Level Attributes
Model-Level implementation IValidatableObject
The problem is, at each step of the way...
If any validators are invalid, Validator.ValidateObject will abort validation and return the failure(s)
Issue - Model Binder Fields
Another possible issue is that the model binder will only run validation on objects that it has decided to bind. For example, if you don't provide inputs for fields within complex types on your model, the model binder won't need to check those properties at all because it hasn't called the constructor on those objects. According to Brad Wilson's great article on Input Validation vs. Model Validation in ASP.NET MVC:
The reason we don't "dive" into the Address object recursively is that there was nothing in the form that bound any values inside of Address.
Solution - Validate Object at the same time as Properties
One way to solve this problem is to convert object-level validations to property level validation by adding a custom validation attribute to the property that will return with the validation result of the object itself.
Josh Carroll's article on Recursive Validation Using DataAnnotations provides an implementation of one such strategy (originally in this SO question). If we want to validate a complex type (like Address), we can add a custom ValidateObject attribute to the property, so it is evaluated on the first step
public class Person {
[Required]
public String Name { get; set; }
[Required, ValidateObject]
public Address Address { get; set; }
}
You'll need to add the following ValidateObjectAttribute implementation:
public class ValidateObjectAttribute: ValidationAttribute {
protected override ValidationResult IsValid(object value, ValidationContext validationContext) {
var results = new List<ValidationResult>();
var context = new ValidationContext(value, null, null);
Validator.TryValidateObject(value, context, results, true);
if (results.Count != 0) {
var compositeResults = new CompositeValidationResult(String.Format("Validation for {0} failed!", validationContext.DisplayName));
results.ForEach(compositeResults.AddResult);
return compositeResults;
}
return ValidationResult.Success;
}
}
public class CompositeValidationResult: ValidationResult {
private readonly List<ValidationResult> _results = new List<ValidationResult>();
public IEnumerable<ValidationResult> Results {
get {
return _results;
}
}
public CompositeValidationResult(string errorMessage) : base(errorMessage) {}
public CompositeValidationResult(string errorMessage, IEnumerable<string> memberNames) : base(errorMessage, memberNames) {}
protected CompositeValidationResult(ValidationResult validationResult) : base(validationResult) {}
public void AddResult(ValidationResult validationResult) {
_results.Add(validationResult);
}
}
Solution - Validate Model at the Same time as Properties
For objects that implement IValidatableObject, when we check the ModelState, we can also check to see if the model itself is valid before returning the list of errors. We can add any errors we want by calling ModelState.AddModelError(field, error). As specified in How to force MVC to Validate IValidatableObject, we can do it like this:
[HttpPost]
public ActionResult Create(Model model) {
if (!ModelState.IsValid) {
var errors = model.Validate(new ValidationContext(model, null, null));
foreach (var error in errors)
foreach (var memberName in error.MemberNames)
ModelState.AddModelError(memberName, error.ErrorMessage);
return View(post);
}
}
Also, if you want a more elegant solution, you can write the code once by providing your own custom model binder implementation in Application_Start() with ModelBinderProviders.BinderProviders.Add(new CustomModelBinderProvider());. There are good implementations here and here
I also ran into this, and found this thread. Here's a first pass:
namespace Foo
{
using System.ComponentModel.DataAnnotations;
using System.Linq;
/// <summary>
/// Attribute class used to validate child properties.
/// </summary>
/// <remarks>
/// See: http://stackoverflow.com/questions/2493800/how-can-i-tell-the-data-annotations-validator-to-also-validate-complex-child-pro
/// Apparently the Data Annotations validator does not validate complex child properties.
/// To do so, slap this attribute on a your property (probably a nested view model)
/// whose type has validation attributes on its properties.
/// This will validate until a nested <see cref="System.ComponentModel.DataAnnotations.ValidationAttribute" />
/// fails. The failed validation result will be returned. In other words, it will fail one at a time.
/// </remarks>
public class HasNestedValidationAttribute : ValidationAttribute
{
/// <summary>
/// Validates the specified value with respect to the current validation attribute.
/// </summary>
/// <param name="value">The value to validate.</param>
/// <param name="validationContext">The context information about the validation operation.</param>
/// <returns>
/// An instance of the <see cref="T:System.ComponentModel.DataAnnotations.ValidationResult"/> class.
/// </returns>
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
var isValid = true;
var result = ValidationResult.Success;
var nestedValidationProperties = value.GetType().GetProperties()
.Where(p => IsDefined(p, typeof(ValidationAttribute)))
.OrderBy(p => p.Name);//Not the best order, but at least known and repeatable.
foreach (var property in nestedValidationProperties)
{
var validators = GetCustomAttributes(property, typeof(ValidationAttribute)) as ValidationAttribute[];
if (validators == null || validators.Length == 0) continue;
foreach (var validator in validators)
{
var propertyValue = property.GetValue(value, null);
result = validator.GetValidationResult(propertyValue, new ValidationContext(value, null, null));
if (result == ValidationResult.Success) continue;
isValid = false;
break;
}
if (!isValid)
{
break;
}
}
return result;
}
}
}
You will need to make your own validator attribute (eg, [CompositeField]) that validates the child properties.