如何在linq join中调用自定义扩展方法

问题描述

我有两张桌子员工和部门。我需要在电话号码上加入内心。这里的问题是员工表包含的电话号码如'1234567890'（10）。但在部门表格中，如果一个人有三个电话号码，则会像1234567890234567890212345654321那样存储。不连续的字符串表示没有逗号，没有空格。我需要比较部门表电话号码的每10位数与员工表电话号码。我怎么能得到它。

提前致谢。

员工

id电话号码

1 1234567890



部门

dept_id电话号码

30 12345678963910453678


$ b来自员工的
$ b加入部门的部门

on emp.phoneno等于dept.phoneno



PLZ帮助



谢谢，

Bony

Hi,

I have two tables employee and department. I need to innerjoin on phone numbers. Here the problem is Employee table contains phone nos like '1234567890' (10) digits. But in department table if a person has three phone numbers they are stored like '1234567890234567890212345654321' like that .continuous string representation no commas,no spaces. I need to compare on every 10 digits of department table phone no with employee table phone no. How Can I get it.
Thanks in advance.
Employee
id phone no
1 1234567890

department
dept_id Phone no
30 12345678963910453678

from emp in employee
join dept in department
on emp.phoneno equals dept.phoneno

PLZ help

Thanks,
Bony

推荐答案

public static class Splitter {
   public static List<string> SplitByLength(this string theString, int length) {
      List<string> returnList = new List<string>();

      try {
         for (int counter = 0; counter < theString.Length; counter += length) {
            returnList.Add(theString.Substring(counter, length));
         }
      } catch (System.Exception exception) {
         MessageBox.Show(exception.Message, "Now this was a surprise");
      }

      return returnList;
   }
}</string></string></string>

和使用示例

And the usage example

List<string> a_list = new List<string>();
List<string> b_list = new List<string>();

a_list.Add("1234567890");
a_list.Add("3910453678");

b_list.Add("12345678963910453678");
b_list.Add("123456789023456789021234565432");

var q1 = from item1 in a_list
         join item2 in b_list
         on 1 equals 1
         where item2.SplitByLength(10).Contains(item1)
         select new {
            i1 = item1,
            i2 = item2
         };

foreach (var a1 in q1) { }</string></string></string></string>

但是，如果这是一个您正在使用的数据库，例如使用Entity Framework，上面的查询将表现得非常糟糕，例如来自性能观点。

However, as said if this is a database you're using for example with Entity Framework, the query above will perform extremely badly for example from performance point of view.

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