ASP.NET date range constraint/validation - asp.net-mvc

Question

If I have a model that tracks employees request for holidays, how would I go about ensuring that an employee does not take multiple holidays within the same date range? Would this be handled with validation or creating a constraint in SQL Server? I used database first for this project.
public partial class HolidayRequestForm
{
public int RequestID { get; set; }
public int EmployeeID { get; set; }
[DisplayFormat(DataFormatString = "{0:dd/MM/yy}", ApplyFormatInEditMode = true)]
public System.DateTime StartDate { get; set; }
[DisplayFormat(DataFormatString = "{0:dd/MM/yy}", ApplyFormatInEditMode = true)]
public System.DateTime FinishDate { get; set; }
[Range(0.0001, int.MaxValue, ErrorMessage = "Hours Requested must be greater than zero. ")]
public decimal HoursTaken { get; set; }
public string Comments { get; set; }
public int YearCreated { get; set; }
public int MonthCreated { get; set; }
public int DayCreated { get; set; }
public Nullable<int> YearOfHoliday { get; set; }
[UIHint("Boolean.cshtml")]
public Nullable<bool> Approved { get; set; }
public string SubmittedBy { get; set; }
public string ApprovedBy { get; set; }
public virtual Employee Employee { get; set; }
}
Ideally I'd like that two employees can request the same date range but a single employee cannot request two holidays within the same date range. Could I use custom validation attribute maybe??

Answer 1

The given scenario is a business logic so it is better to implement this in your code itself instead of database constrains or triggers.
You can create a custom validator for the same and do a validation in the business layer. This approach will be easy maintainable/upgradable.
Use a normal method for validation , or create custom ValidationAttribute by inhering ValidationAttribute and by overriding IsValid method.