Billing: fix calculation

Elwig/Models/DeliveryPartBucket.cs

@@ -0,0 +1,28 @@
+using Microsoft.EntityFrameworkCore;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Elwig.Models {
+    [Table("delivery_part_bucket"), PrimaryKey("Year", "DId", "DPNr", "BktNr")]
+    public class DeliveryPartBucket {
+        [Column("year")]
+        public int Year { get; set; }
+
+        [Column("did")]
+        public int DId { get; set; }
+
+        [Column("dpnr")]
+        public int DPNr { get; set; }
+
+        [Column("bktnr")]
+        public int BktNr { get; set; }
+
+        [Column("discr")]
+        public string Discr { get; set; }
+
+        [Column("value")]
+        public int Value { get; set; }
+
+        [ForeignKey("Year, DId, DPNr")]
+        public virtual DeliveryPart Part { get; private set; }
+    }
+}