Conditionally required property using data annotations

Question

I have a class like this:

public class Document {    public int DocumentType{get;set;}     [Required]    public string Name{get;set;}     [Required]    public string Name2{get;set;} } 

Now if I put a [Required] data annotation on the Name and Name2 properties, then everything is ok and if Name or Name2 are empty, validation will throw an error.

But I want Name field only to be required if DocumentType is equal to 1 and Name2 only required if DocumentType is equal to 2 .

public class Document {    public int DocumentType{get;set;}     [Required(Expression<Func<object, bool>>)]    public string Name{get;set;}     [Required(Expression<Func<object, bool>>)]    public string Name2{get;set;} } 

but I know I can't, it causes an error. What should I do for this requirement?

Answer 1

RequiredIf validation attribute

I've written a RequiredIfAttribute that requires a particular property value when a different property has a certain value (what you require) or when a different property has anything but a specific value.

This is the code that may help:

/// <summary> /// Provides conditional validation based on related property value. /// </summary> [AttributeUsage(AttributeTargets.Property, AllowMultiple = false)] public sealed class RequiredIfAttribute : ValidationAttribute {     #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      /// <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;     } }