Use Fluent Validation to compare values in an array

Question

I have an array of objects I am receiving in an HTTP Post body. Looks something like this:

{
  load: {
     stops: [
          { 
            Name: "Stop 1",
            AppointmentDateTime: "02/25/2025T14:00:00"
          },
          { 
            Name: "Stop 2",
            AppointmentDateTime: "02/25/2025T13:00:00"
          },
          { 
            Name: "Stop 3",
            AppointmentDateTime: "02/25/2025T15:30:00"
          }
      ]
   }
}

I have already got a fluid validator in C# working with some of the following code:

RuleForEach(x => x.Stops).ChildRule(stop => 
{
   stop.RuleFor(s => s.Name).NotEmpty().NotNull();
   stop.RuleFor(s => s.AppointmentDateTime).NotEmpty().NotNull().Must(x => x > x.DateTime.Now).WithMessage("AppointmentDateTime must be in the future");
}

While this works, I would like to validate that the items in the array are after each other. Stop 2 should have an appointment time after stop 1 and stop 3 after stop 2 etc. I can't find a way in the code to do something like a for loop where I can save the previous item value. Ideally I was going to do something like:

Stop? prevStop = null;
foreach (stop in stops) {
  if (!prevStop is null)
    {
     DO SOMETHING TO validate that prevStop.AppointmentDateTime > stop.AppointmentDateTime;
    }
  prevStop = stop;
}

While there is a foreach like way of testing the items, I don't see a way to save the previous item for comparison to the current one.

Answer 1

you can create Custom Validator as follows :

public class LoadValidator : AbstractValidator<Load>
{
    public LoadValidator()
    {
        RuleForEach(x => x.Stops).ChildRule(stop =>
        {
            stop.RuleFor(s => s.Name).NotEmpty().NotNull();
            stop.RuleFor(s => s.AppointmentDateTime).NotEmpty().NotNull().Must(x => x > DateTime.Now).WithMessage("AppointmentDateTime must be in the future");
        });

        RuleFor(x => x.Stops).Must(stops => BeInChronologicalOrder(stops)).WithMessage("Stops must be in chronological order");
    }

    private bool BeInChronologicalOrder(Stop[] stops)
    {
        if (stops == null || stops.Length <= 1)
        {
            return true;
        }

   
        //iterate through the array
        //and compare the AppointmentDateTime of the current stop 
        //with the AppointmentDateTime of the previous stop.
        //If any stop's appointment time
        //is not after the previous stop's appointment time, the   validation fails,
        //and the method returns false.
       
        for (int i = 1; i < stops.Length; i++)
        {
            if (stops[i].AppointmentDateTime <= stops[i - 1].AppointmentDateTime)
            {
                return false;
            }
        }

        return true;
    }
}