LINQ- Max in where condition

Question

I have a class TaskWeekUI with this definition:

 public class TaskWeekUI    {
   public Guid TaskWeekId { get; set; }
   public Guid TaskId { get; set; }
   public Guid WeekId { get; set; }
   public DateTime EndDate { get; set; }
   public string PersianEndDate { get; set; }
   public double PlanProgress { get; set; }
   public double ActualProgress { get; set; }    } 

and I wrote this query :

 TaskWeekUI ti =  tis.First( t => t.PlanProgress > 0 && t.EndDate ==  tis.Where(p => p.PlanProgress != null && p.PlanProgress > 0).Max(w => w.EndDate));

Is this query is true? Can I write my query better than this?

Answer 1

I think you want the one whose PlanProgress > 0 has a most recent EndDate.

TaskWeekUI ti = tis.Where(t => t.PlanProgress > 0)
                   .OrderByDescending(t => t.EndDate)
                   .FirstOrDefault();

Answer 2

This query seems to be correct from point of view of result obtained.

But in your inner query tis.Where(p => p.PlanProgress != null && p.PlanProgress > 0).Max(w => w.EndDate) is computed for each element in collection with t.PlanProgress > 0

So its a better way to obtain Max value outside of a query as follows:

var max = tis.Where(p => p.PlanProgress != null && p.PlanProgress > 0).Max(w => w.EndDate);
tis.First( t => t.PlanProgress > 0 && t.EndDate == max);

Going further p.PlanProgress != null is allways true since p.PlanProgress is not of Nullable type. So our code becomes like this:

var max = tis.Where(p => p.PlanProgress > 0).Max(w => w.EndDate);
    tis.First( t => t.PlanProgress > 0 && t.EndDate == max);

Or you can change a definition of your class and make p.PlanProgress of Nullable type:

public class TaskWeekUI    {
   public Guid TaskWeekId { get; set; }
   public Guid TaskId { get; set; }
   public Guid WeekId { get; set; }
   public DateTime EndDate { get; set; }
   public string PersianEndDate { get; set; }
   public double? PlanProgress { get; set; }
   public double ActualProgress { get; set; }    
} 

var max = tis.Where(p => p.PlanProgress.HasValue && p.PlanProgress.Value > 0).Max(w => w.EndDate);
    tis.First( t => t.PlanProgress.HasValue && t.PlanProgress.Value > 0 && t.EndDate == max);