Conditionally required property using data annotations
Solution 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;
}
}
Solution 2:
Conditionally required property using data annotations
[RequiredIf(dependent Property name, dependent Property value)]
e.g.
[RequiredIf("Country", "Ethiopia")]
public string POBox{get;set;}
// POBox is required in Ethiopia
public string Country{get;set;}
[RequiredIf("destination", "US")]
public string State{get;set;}
// State is required in US
public string destination{get;set;}
public class RequiredIfAttribute : ValidationAttribute
{
RequiredAttribute _innerAttribute = new RequiredAttribute();
public string _dependentProperty { get; set; }
public object _targetValue { get; set; }
public RequiredIfAttribute(string dependentProperty, object targetValue)
{
this._dependentProperty = dependentProperty;
this._targetValue = targetValue;
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
var field = validationContext.ObjectType.GetProperty(_dependentProperty);
if (field != null)
{
var dependentValue = field.GetValue(validationContext.ObjectInstance, null);
if ((dependentValue == null && _targetValue == null) || (dependentValue.Equals(_targetValue)))
{
if (!_innerAttribute.IsValid(value))
{
string name = validationContext.DisplayName;
string specificErrorMessage = ErrorMessage;
if (specificErrorMessage.Length < 1)
specificErrorMessage = $"{name} is required.";
return new ValidationResult(specificErrorMessage, new[] { validationContext.MemberName });
}
}
return ValidationResult.Success;
}
else
{
return new ValidationResult(FormatErrorMessage(_dependentProperty));
}
}
}
Solution 3:
Out of the box I think this is still not possible.
But I found this promising article about Mvc.ValidationToolkit (also here, unfortunately this is only alpha, but you probably could also just extract the method(s) you need from this code and integrate it on your own), it contains the nice sounding attribute RequiredIf which seems to match exactly your cause:
- you download the project from the linked zip and build it
- get the built dll from your build folder and reference it in the project you are using
- unfortunately this seems to require reference to MVC, too (easiest way to have that is starting an MVC-Project in VS or
install-package Microsoft.AspNet.Mvc) - in the files where you want to use it, you add
using Mvc.ValidationToolkit; - then you are able to write things like
[RequiredIf("DocumentType", 2)]or[RequiredIf("DocumentType", 1)], so objects are valid if neithernameorname2are supplied as long asDocumentTypeis not equal to 1 or 2
Solution 4:
Check out Fluent Validation
https://www.nuget.org/packages/FluentValidation/
Project Description A small validation library for .NET that uses a fluent interface and lambda expressions for building validation rules for your business objects.
https://github.com/JeremySkinner/FluentValidation
Solution 5:
I have always used implemented IValidatableObject from System.ComponentModel.DataAnnotations;
Example below
public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
if (this.SendInAppNotification)
{
if (string.IsNullOrEmpty(this.NotificationTitle) || string.IsNullOrWhiteSpace(this.NotificationTitle))
{
yield return new ValidationResult(
$"Notification Title is required",
new[] { nameof(this.NotificationTitle) });
}
}