How to put conditional Required Attribute into class property to work with WEB API?

Question

I just want to put conditional Required Attribute which is work with WEB API

Example

public sealed class EmployeeModel
{
      [Required]
      public int CategoryId{ get; set; }
      public string Email{ get; set; } // If CategoryId == 1 then it is required
}

I am using Model State validation via (ActionFilterAttribute)

Answer 1

You can implement your own ValidationAttribute. Perhaps something like this:

public class RequireWhenCategoryAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var employee = (EmployeeModel) validationContext.ObjectInstance;
        if (employee.CategoryId == 1)
            return ValidationResult.Success;

        var emailStr = value as string;
        return string.IsNullOrWhiteSpace(emailStr)
            ? new ValidationResult("Value is required.")
            : ValidationResult.Success;
    }
}

public sealed class EmployeeModel
{
    [Required]
    public int CategoryId { get; set; }
    [RequireWhenCategory]
    public string Email { get; set; } // If CategoryId == 1 then it is required
}

This is just a sample. It may have casting issues, and I'm not sure this is the best approach to solve this problem.