fix: adding unique constraint for screening id and nhs number (#1712)

fix: adding unique constraint for screening id and nhs number

Author: SamRobinson75684

application/CohortManager/src/Functions/Shared/DataServices.Database/DataServicesContext.cs

@@ -44,7 +44,8 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
 
         modelBuilder.Entity<ParticipantManagement>()
             .ToTable("PARTICIPANT_MANAGEMENT", "dbo")
-            .HasIndex(i => new { i.NHSNumber, i.ScreeningId }, "ix_PARTICIPANT_MANAGEMENT_screening_nhs");
+            .HasIndex(i => new { i.NHSNumber, i.ScreeningId }, "ix_PARTICIPANT_MANAGEMENT_screening_nhs")
+            .IsUnique();
 
         modelBuilder.Entity<ParticipantDemographic>()
             .ToTable("PARTICIPANT_DEMOGRAPHIC", "dbo")