截取字符串

Question

因为字符串超出数据库字段定义的长度，出现异常。“更新条目时出错。有关详细信息，请参见内部异常。”然后我就用substring（0，399） ，但是没有超出的字符串，比如只有200个字符，就会报错：索引和长度必须引用该字符串内的位置。  参数名: length用substring之前，必须要判断下：  
book.Author = (latestBook.Author.Length > 400 ? latestBook.Author.Substring(0, 400) :  latestBook.Author);我觉得还是挺长的，有没有string自带的更短的函数？
        /// <summary>
        /// 更新 Library 的状态：文档pdf2swf转换后，更新状态、swf页数等信息。 
        /// 被引用：ConvertToSwf.cs
        /// </summary>
        /// <param name="latestBook"></param>
        public static void Update(Library latestBook)
        {
            using (var db = new WEBVODEntities())
            {
                Library book =  db.Library.SingleOrDefault(a => a.Guid == latestBook.Guid);
                book.Status = latestBook.Status;
                book.FlvCount = latestBook.FlvCount;
                book.Content = latestBook.Content;
                book.FlvTime = DateTime.Now;
                book.HasPic = latestBook.HasPic;
                book.Author = latestBook.Author;
                book.AuthorOrg = latestBook.AuthorOrg;
                book.MagName = latestBook.MagName;
                book.TimePdf2Swf = latestBook.TimePdf2Swf;
                db.SaveChanges();
                
            } 
        }

Answer 1

用存储过程，在存储过程里定义变量为400，会自动截断的。mysql这样了。

Answer 2

book.Author = (latestBook.Author.Length > 400 ? latestBook.Author.Substring(0, 400) :  latestBook.Author);现在还有一个问题，还要判断latestBook.Author是否为空，不然赋值也要出现错误。

Answer 3

book.Author = (latestBook.Author.Length > 400 &&!string.isnullorempty( latestBook.Author)? latestBook.Author.Substring(0, 400) :  latestBook.Author);

Answer 4

谢谢，!string.isnullorempty( latestBook.Author)这个要写前边，不然latestBook.Author==null的话，latestBook.Author.Length > 400就会引发异常

Answer 5

 public static class StringExtend
    {
        public static string CutOut(this string str,int length)
        {
            if (str == null)
                return null;
            if (str.Length < length)
                return str;
            return str.Substring(0, length);
        }
    } var s = "12345";
            Console.WriteLine( s.CutOut(1));
            Console.WriteLine(s.CutOut(3));
            Console.WriteLine(s.CutOut(5));
            Console.WriteLine(s.CutOut(7));
            Console.WriteLine(s.CutOut(8));你可以自己扩展一个