Question

I’d like to transform these Entity Framework’s properties into SQL Server’s computed columns. Is it possible? All other properties specified are table fields.
Moreover, considering that I am using Code First, how I should specify the computed columns inside my model?

public enum Severity : int { INTIME = 0, B = 1, M = 2, A = 3, TIMEOUT = 4 };
public enum StatiTT : int { ND_INT = 1, ND_REP = 2, INT = 3, DI = 4, CH = 5, RV = 6, AN = 7 };
private const float TRESH_B = (float)0.5;
private const float TRESH_M = (float)0.3;
private const float TRESH_A = (float)0.2;

A)

 public int MinutiAllaScadenza
   {
       get
       {
           int mm = 0;
           DateTime Ora = DateTime.Now;

           mm = (DataObiettivo - Ora).Days*1440 + (DataObiettivo - Ora).Hours * 60 + (DataObiettivo - Ora).Minutes;

           if (StatoTicketID > (int)StatiTT.DI && mm < 0) mm = 10000000; 

           return mm;
       }
   }

B)

public int Sev 
   {
       get
       {
           int sev = 0; 
           float perctres = PercentualeTempoResiduo; 

           if (StatoTicketID < (int)StatiTT.CH)
           {
               if (MinutiAllaScadenza < 0) { sev = (int)Severity.TIMEOUT; return sev; }
               if (perctres < TRESH_A) { sev = (int)Severity.A; return sev; }
               if (perctres < TRESH_M) { sev = (int)Severity.M; return sev; }
               if (perctres < TRESH_B) { sev = (int)Severity.B; return sev; }
           }
           return sev;
       }
   }

C)

public float PercentualeTempoResiduo
   {
       get
       {

           if (StatoTicketID > (int)StatiTT.DI) return 999;

           float perc = 0;
           float mm2scad = (float)MinutiAllaScadenza;
           float mmtot = (float)TempoTotaleInizio_Obiettivo;

           if (MinutiAllaScadenza > 0)

               perc = (float)1 - (mmtot-mm2scad) / mmtot;

           return perc;
       }
   }

D)

   public string Alert
   {
       get
       {
           string alert = "";
           float perctres = PercentualeTempoResiduo; 

           if (StatoTicketID < (int)StatiTT.CH) {
               if (perctres < TRESH_A) { alert = "A"; return alert; }
               if (perctres < TRESH_M) { alert = "M"; return alert; }
               if (perctres < TRESH_B) { alert = "B"; return alert; }
           }
           return alert;
       }
   }

Thank you very much!

Answer 1

The answer to your main question is yes, these C# routines can be converted to computed columns. But there’s one condition: the relevant information needed to compute the result must be found in the table itself.

For your Alert property, here’s how your computed column would look:

alter table <TBLNAME> add <COLNAME>  AS (
  case 
    when StatoTicketID < (int)StatiTT.CH AND perctres < .2 then 'A'
    when StatoTicketID < (int)StatiTT.CH AND perctres < .3 then 'M'
    when StatoTicketID < (int)StatiTT.CH AND perctres < .5 then 'B'
    else ''
  end)

If your computed result needs to use information from other tables then consider binding EF to a view for reading and then using plain EF objects for your write operations.

As for code first, you cannot write a computed column in C# and expect EF to translate that into a SQLServer computed column for you. Write the computed column in the DB after you’ve done your model first generating and then go back and wire it into your EF object.