使用EF进行简单的增删改查

CREATE TABLE `objinfo` (
`Id` int(11) NOT NULL,
`ObjName` varchar(255) DEFAULT NULL,
`ObjType` int(255) DEFAULT NULL,
`ObjPrice` decimal(10,0) DEFAULT NULL,
`ObjSellPrice` decimal(10,0) DEFAULT NULL,
`ObjIcon` varchar(255) DEFAULT NULL,
`AddAttack` int(255) DEFAULT NULL,
`AddDefence` int(255) DEFAULT NULL,
`AddTili` int(255) DEFAULT NULL,
`AddExp` int(255) DEFAULT NULL,
PRIMARY KEY (`Id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

  private static void Add()
        {
            arpgdbEntities dbContext = new arpgdbEntities();
            objinfo obj = new objinfo
            {
                AddDefence = 1,
                AddAttack = 2,
                AddExp = 3,
                AddTili = 4,
                Id = 6,
                ObjIcon = "",
                ObjName = "青铜戒指",
                ObjPrice = 10,
                ObjSellPrice = 5,
                ObjType = 1
            };
            dbContext.objinfo.Add(obj);
            int result = dbContext.SaveChanges();
            if (result > 0)
            {
                Console.WriteLine("保存成功");
            }
        }

        // 删除现在出了问题
        private static void Del()
        {
            arpgdbEntities dbContext = new arpgdbEntities();
            // 先查出来
            var objs = from c in dbContext.objinfo
                       where c.Id == 3
                       select c;
            dbContext.Entry(objs.ToList().FirstOrDefault()).State = EntityState.Deleted;
            if (dbContext.SaveChanges() > 0)
            {
                Console.WriteLine("删除成功");
            }
        }

        private static void Modify()
        {
            arpgdbEntities dbContext = new arpgdbEntities();
            // 先查出来一个
            var objs = from c in dbContext.objinfo
                       where c.Id == 1
                       select c;
            objinfo obj = objs.ToList().FirstOrDefault();
            obj.ObjName = "强化戒指";  // 如果在这儿修改了主键怎么办，如果数据库中没有设置主键怎么办
            obj.ObjIcon = "addd";
            dbContext.Entry(obj).State = EntityState.Modified;
            int result = dbContext.SaveChanges();
            if (result > 0)
            {
                Console.WriteLine("修改成功");
            }

        }

        private static void Select()
        {
            arpgdbEntities dbContext = new arpgdbEntities();
            var objs = from c in dbContext.objinfo
                       select c;
            foreach (objinfo objinfo in objs.ToList())
            {
                Console.WriteLine(objinfo.Id);
            }
        }