fix: adding unique constraint for nhs number in demographic table (#1713)

fix: adding unique constraint for nhs number

Author: SamRobinson75684

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

@@ -49,7 +49,8 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
 
         modelBuilder.Entity<ParticipantDemographic>()
             .ToTable("PARTICIPANT_DEMOGRAPHIC", "dbo")
-            .HasIndex(i => new { i.NhsNumber }, "Index_PARTICIPANT_DEMOGRAPHIC_NhsNumber");
+            .HasIndex(i => new { i.NhsNumber }, "Index_PARTICIPANT_DEMOGRAPHIC_NhsNumber")
+            .IsUnique();
 
         modelBuilder.Entity<GeneCodeLkp>()
             .ToTable("GENE_CODE_LKP", "dbo");