C# 将Linq更新为实体时排除列

我正在尝试存储更新日期并为所有记录创建日期

我为SaveChanges方法添加了覆盖，当我更新一条记录时，CreatedDate将变为null。所以我的问题是，在更新时，我如何保持CreatedDate不变

    public override int SaveChanges()
    {
        try
        {
            var changeSet = ChangeTracker.Entries();
            dynamic obj;
            if (changeSet != null)
            {
                foreach (var entry in changeSet.Where(c => c.State == EntityState.Added))
                {
                    obj = entry.Entity;
                    obj.CreatedDate = DateTime.UtcNow;
                }
                foreach (var entry in changeSet.Where(c => c.State == EntityState.Modified))
                {
                    obj = entry.Entity;
                    obj.ModifiedDate = DateTime.UtcNow;
                }
            }
        }
        catch (Exception ex)
        {
            throw;
        }
        return base.SaveChanges();
    }

---

很简单，更新时不要传递CreateDate

 if (changeSet != null)
            {
                foreach (var entry in changeSet.Where(c => c.State == EntityState.Added))
                {
                    obj = entry.Entity;

                }
                foreach (var entry in changeSet.Where(c => c.State == EntityState.Modified))
                {
                    obj = entry.Entity;

                }
            }

---

一般建议-为什么不使用if-else将这2个循环合并为1？@Bakri没关系，如果有新的日期，则添加验证，然后通过