无法将NULL插入表（主键）

Question

我想将我的模型插入数据库

EventAdditionalSell eas = new EventAdditionalSell();
eas.EventNoteID = en.EventID; (e.g 100 which exists in datatable)
eas.Person = mdl.Person; (string - can be just "")

db.EventAdditionalSells.Add(eas);
db.SaveChanges();

我总是得到一个例外

  

无法将值NULL插入到'EventAdditionalSellID'列中，表'1028_test.dbo.EventAdditionalSells';列不允许空值。 INSERT失败。

我的课程：

public class EventAdditionalSell
{
        [Key]
        public int EventAdditionalSellID { get; set; }

        [Display(Name = "Kupujący")]
        public string Person { get; set; }

        public int EventNoteID { get; set; }
        public virtual EventNote EventNote { get; set; }
        public virtual List<PaintballItem> PaintballItems { get; set; }
    }

这里有什么问题？