在linq中得到最后一行 [英] get last row in linq

问题描述

我有1个表有PK是字符串我不能得到最后一行
当我使用按代码desc

I have 1 table that have PK is string I can't get last row when I use order by code desc

9999 不正确

73858 正确

帮助我请T__T

我来自泰国对不起，如果语言不正确

I'm from Thailand sorry if incorrect language

========================================= ========================
这个问题是由 grek40 非常感谢你

======================================================================= This problem is solve by grek40 Thank you so much

var lastrow = db.table.OrderByDescending（x => x.Code.Length）.ThenByDescending（ x => x.Code）.FirstOrD efault（）。Code;

var lastrow = db.table.OrderByDescending(x => x.Code.Length).ThenByDescending(x => x.Code).FirstOrDefault().Code;

推荐答案

由于您的代码使用字符串算术比较字符串值，其中 9999 更大 73858 ，因为它以 9 。你想要的是数字算术，所以首先将你的字符串转换成数字。不幸的是，你不能在EF中使用 int.TryParse 或 Convert.ToInt32 ，所以你不会转换你的查询到 IEnumerable first：

As your Code-property is a string values are compared using string-arithmetic where 9999 is greater 73858 as it starts with 9. What you want is number-arithmetic, so convert your strings to numbers first. Unfortunately you can´t use int.TryParse or Convert.ToInt32 in EF, so you´re stuck on converting your query to an IEnumerable first:

var query = myQuery.AsEnumerable();

现在您可以转换每个字符串并获取实际的最后一行

Now you can convert every string and get the actual last row

var lastRow = query.OrderByDescending(o => Convert.ToInt32(o.Code)).FirstOrDefault().Code

这意味着你必须将所有的数据都存入内存，以获得最大的价值，当你有很多行时可能是一个问题

This means you´d have to get all the data into memory in order to get the greatest value which might be an issue when you have many rows.

无论如何，其他人已经指出，您应该考虑使用允许此类搜索行为的数据类型。那么你可以从一开始就很容易地避免这些情况。

Anyway as others already pointed out you should consider to use a datatype that allows this kind of search-behaviour. Then you could easily avoid these situations from the very beginning.

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