EF并发异常处理

 [Table("SYS_EMP")]
    public class Emp
    {
        [Key]
        public int Id { get; set; }
        [Column("EMP_CODE")]
        public string EmpCode { get; set; }
        public string NAME { get; set; }
        public string USRID { get; set; }
        public int NUM { get; set; }
        [Timestamp]
        public byte[] version { get; set; }
    }

        /// <summary>
        /// 处理并发冲突（点赞场景）
        /// https://docs.microsoft.com/zh-cn/ef/ef6/saving/concurrency?redirectedfrom=MSDN
        /// </summary>
        public void UpdateEmp()
        {
            EmpDbContext Context1 = new EmpDbContext();
            var emp= Context1.Emp.Where(x=>x.EmpCode == "001").FirstOrDefault();
            emp.NUM += 1;
            Context1.Entry<Emp>(emp).State = System.Data.Entity.EntityState.Modified;
            Context1.Emp.AddOrUpdate(emp);

            EmpDbContext Context2 = new EmpDbContext();
            var emp2 = Context2.Emp.Where(x => x.EmpCode == "001").FirstOrDefault();
            emp2.NUM += 1;
            Context2.Entry<Emp>(emp2).State = System.Data.Entity.EntityState.Modified;
            Context2.Emp.AddOrUpdate(emp2);
            int aa = Context2.SaveChanges();

            bool saveFailed;
            do
            {
                saveFailed = false;
                try
                {
                    Context1.SaveChanges();
                }
                catch (DbUpdateConcurrencyException ex)
                {
                    saveFailed = true;
                    ex.Entries.Single().Reload();
                    var entry = ex.Entries.Single();
                    var databaseValues = entry.GetDatabaseValues();
                    databaseValues["NUM"]=databaseValues["NUM"] == null ? 1 : (int)databaseValues["NUM"]+1;
                    entry.CurrentValues.SetValues(databaseValues);
                }
            } while (saveFailed);
        }