I know this question is from a long time ago but someone asked in the comments section of Robert's answer how to use unobtrusive as part of the solution.
I wanted client side validation as well so I'm sharing my revised code to Robert's original code. It's essentially the same code except it implements IClientModelValidator and has an additional AddValidation method. The client validation still respects the IsInverted property.
Implement IClientModelValidator
public sealed class RequiredIfAttribute : ValidationAttribute, IClientModelValidator
New AddValidation method
public void AddValidation(ClientModelValidationContext context)
{
var viewContext = context.ActionContext as ViewContext;
var modelType = context.ModelMetadata.ContainerType;
var instance = viewContext?.ViewData.Model;
var model = instance?.GetType().Name == modelType.Name
? instance
: instance?.GetType()?.GetProperties().First(x => x.PropertyType.Name == modelType.Name)
.GetValue(instance, null);
object otherValue = modelType.GetProperty(this.OtherProperty)?.GetValue(model, null);
object value = modelType.GetProperty(context.ModelMetadata.Name)?.GetValue(model, null);
string displayName = context.ModelMetadata.DisplayName ?? context.ModelMetadata.Name;
string errorMessage = null;
// check if this value is actually required and validate it
if (!this.IsInverted && object.Equals(otherValue, this.OtherPropertyValue) ||
this.IsInverted && !object.Equals(otherValue, this.OtherPropertyValue))
{
if (value == null)
{
errorMessage = this.FormatErrorMessage(displayName);
}
// additional check for strings so they're not empty
string val = value as string;
if (val != null && val.Trim().Length == 0)
{
errorMessage = this.FormatErrorMessage(displayName);
}
}
if (!string.IsNullOrWhiteSpace(errorMessage))
{
context.Attributes.Add("data-val", "true");
context.Attributes.Add("data-val-required", errorMessage);
}
}
Full Code
/// <summary>
/// Provides conditional validation based on related property value.
/// </summary>
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
public sealed class RequiredIfAttribute : ValidationAttribute, IClientModelValidator
{
#region Properties
/// <summary>
/// Gets or sets the other property name that will be used during validation.
/// </summary>
/// <value>
/// The other property name.
/// </value>
public string OtherProperty { get; private set; }
/// <summary>
/// Gets or sets the display name of the other property.
/// </summary>
/// <value>
/// The display name of the other property.
/// </value>
public string OtherPropertyDisplayName { get; set; }
/// <summary>
/// Gets or sets the other property value that will be relevant for validation.
/// </summary>
/// <value>
/// The other property value.
/// </value>
public object OtherPropertyValue { get; private set; }
/// <summary>
/// Gets or sets a value indicating whether other property's value should match or differ from provided other property's value (default is <c>false</c>).
/// </summary>
/// <value>
/// <c>true</c> if other property's value validation should be inverted; otherwise, <c>false</c>.
/// </value>
/// <remarks>
/// How this works
/// - true: validated property is required when other property doesn't equal provided value
/// - false: validated property is required when other property matches provided value
/// </remarks>
public bool IsInverted { get; set; }
/// <summary>
/// Gets a value that indicates whether the attribute requires validation context.
/// </summary>
/// <returns><c>true</c> if the attribute requires validation context; otherwise, <c>false</c>.</returns>
public override bool RequiresValidationContext
{
get { return true; }
}
#endregion
#region Constructor
/// <summary>
/// Initializes a new instance of the <see cref="RequiredIfAttribute"/> class.
/// </summary>
/// <param name="otherProperty">The other property.</param>
/// <param name="otherPropertyValue">The other property value.</param>
public RequiredIfAttribute(string otherProperty, object otherPropertyValue)
: base("'{0}' is required because '{1}' has a value {3}'{2}'.")
{
this.OtherProperty = otherProperty;
this.OtherPropertyValue = otherPropertyValue;
this.IsInverted = false;
}
#endregion
public void AddValidation(ClientModelValidationContext context)
{
var viewContext = context.ActionContext as ViewContext;
var modelType = context.ModelMetadata.ContainerType;
var instance = viewContext?.ViewData.Model;
var model = instance?.GetType().Name == modelType.Name
? instance
: instance?.GetType()?.GetProperties().First(x => x.PropertyType.Name == modelType.Name)
.GetValue(instance, null);
object otherValue = modelType.GetProperty(this.OtherProperty)?.GetValue(model, null);
object value = modelType.GetProperty(context.ModelMetadata.Name)?.GetValue(model, null);
string displayName = context.ModelMetadata.DisplayName ?? context.ModelMetadata.Name;
string errorMessage = null;
// check if this value is actually required and validate it
if (!this.IsInverted && object.Equals(otherValue, this.OtherPropertyValue) ||
this.IsInverted && !object.Equals(otherValue, this.OtherPropertyValue))
{
if (value == null)
{
errorMessage = this.FormatErrorMessage(displayName);
}
// additional check for strings so they're not empty
string val = value as string;
if (val != null && val.Trim().Length == 0)
{
errorMessage = this.FormatErrorMessage(displayName);
}
}
if (!string.IsNullOrWhiteSpace(errorMessage))
{
context.Attributes.Add("data-val", "true");
context.Attributes.Add("data-val-required", errorMessage);
}
}
/// <summary>
/// Applies formatting to an error message, based on the data field where the error occurred.
/// </summary>
/// <param name="name">The name to include in the formatted message.</param>
/// <returns>
/// An instance of the formatted error message.
/// </returns>
public override string FormatErrorMessage(string name)
{
return string.Format(
CultureInfo.CurrentCulture,
base.ErrorMessageString,
name,
this.OtherPropertyDisplayName ?? this.OtherProperty,
this.OtherPropertyValue,
this.IsInverted ? "other than " : "of ");
}
/// <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)
{
if (validationContext == null)
{
throw new ArgumentNullException("validationContext");
}
PropertyInfo otherProperty = validationContext.ObjectType.GetProperty(this.OtherProperty);
if (otherProperty == null)
{
return new ValidationResult(
string.Format(CultureInfo.CurrentCulture, "Could not find a property named '{0}'.", this.OtherProperty));
}
object otherValue = otherProperty.GetValue(validationContext.ObjectInstance);
// check if this value is actually required and validate it
if (!this.IsInverted && object.Equals(otherValue, this.OtherPropertyValue) ||
this.IsInverted && !object.Equals(otherValue, this.OtherPropertyValue))
{
if (value == null)
{
return new ValidationResult(this.FormatErrorMessage(validationContext.DisplayName));
}
// additional check for strings so they're not empty
string val = value as string;
if (val != null && val.Trim().Length == 0)
{
return new ValidationResult(this.FormatErrorMessage(validationContext.DisplayName));
}
}
return ValidationResult.Success;
}
}
This should just work, provided you have included jquery.js, jquery.validate.js and jquery.validate.unobtrusive.js script files (in that order) to your layout or razor view.
