/// <summary>
/// Executes custom server side validation for the model
/// </summary>
/// <param name="validationContext"></param>
/// <returns></returns>
public IEnumerable <ValidationResult> Validate(ValidationContext validationContext)
{
if (PreValueModel.IsRequired && Value.IsNullValueOrEmpty() && !ContentExtensions.HasFile(NewFile))
{
yield return(new ValidationResult("Value is required", new[] { "Value" }));
}
}