Billing: fix calculation

Elwig/Models/WineCult.cs

@@ -1,13 +1,17 @@
 using Microsoft.EntityFrameworkCore;
 using System.ComponentModel.DataAnnotations.Schema;
+using IndexAttribute = Microsoft.EntityFrameworkCore.IndexAttribute;
 
 namespace Elwig.Models {
-    [Table("wine_cultivation"), PrimaryKey("CultId")]
+    [Table("wine_cultivation"), PrimaryKey("CultId"), Index("Name", IsUnique = true)]
     public class WineCult {
         [Column("cultid")]
         public string CultId { get; set; }
 
         [Column("name")]
         public string Name { get; set; }
+
+        [Column("description")]
+        public string Description { get; set; }
     }
 }