Use CountryCode as PK

Elwig/Models/Country.cs

@@ -2,17 +2,17 @@ using Microsoft.EntityFrameworkCore;
 using System.ComponentModel.DataAnnotations.Schema;
 
 namespace Elwig.Models {
-    [Table("country"), PrimaryKey("Alpha2")]
+    [Table("country"), PrimaryKey("Num"), Index("Alpha2", IsUnique = true), Index("Alpha3", IsUnique = true)]
     public class Country {
+        [Column("num")]
+        public int Num { get; private set; }
+
         [Column("alpha2")]
         public string Alpha2 { get; private set; }
 
         [Column("alpha3")]
         public string Alpha3 { get; private set; }
 
-        [Column("num")]
-        public int Num { get; private set; }
-
         [Column("name")]
         public string Name { get; private set; }