Custom ViewModel attribute with own validation logic

[amanbaevsayat]

Please, add feature with adding custom attribute for viewmodel with custom validation logic.

CustomValidationAttribute should have:

• bool IsValid method with Value parameter (type object)
• property string ErrorMessage to response custom error

public class FlightDateValidationAttribute : ValidationAttribute
    {
        public new string ErrorMessage = "Flight date is invalid";
        // or
        public override string Message(){
                  return "Flight date is invalid"; 
        }
        // up to you
        public override bool IsValid(object value)
        {
            var date = value as string;
            return DateTime.TryParse(date, out var flightDate) && flightDate.Date >= DateTime.UtcNow.Date;
        }
    }

In ViewModel:

[FlightDateValidation]
public DateTime FlightDate { get; set; }

or

[FlightDateValidation(ErrorMessage = "Flight date is invalid")] // if message is custom
public DateTime FlightDate { get; set; }

[i4004]

Example:

/// <summary>
/// Indicates that this property should be a valid email address
/// </summary>
[AttributeUsage(AttributeTargets.Property)]
public class EMailAttribute : ValidationAttribute
{
	/// <summary>
	/// Initializes a new instance of the <see cref="EMailAttribute"/> class.
	/// </summary>
	/// <param name="errorMessage">The custom error message, should contain string table item key if 'isMessageFromStringTable' is true.</param>
	/// <param name="isMessageFromStringTable">if set to <c>true</c> then indicates that errorMessage is containing string table item key instead of string error message.</param>
	public EMailAttribute(string errorMessage = null, bool isMessageFromStringTable = true) : base(errorMessage, isMessageFromStringTable)
	{
	}

	/// <summary>
	/// Validates the specified property value.
	/// </summary>
	/// <param name="value">The object value.</param>
	/// <param name="propertyInfo">Information about the property containing this attribute.</param>
	/// <param name="resolver">The objects resolver, useful if you need to retrieve some dependencies to perform validation.</param>
	public override void Validate(object value, PropertyInfo propertyInfo, IDIResolver resolver)
	{
		if (!(value is string))
			return;

		if (StringHelper.ValidateEMail((string)value))
			return;

		TryThrowCustomOrStringTableException(resolver);

		throw new ModelValidationException($"Property '{propertyInfo.Name}' should be an email, actual value: '{value}'");
	}
}