获得当前和先前的价值 [英] Getting current and previous value

问题描述

在下面的LINQ查询中，我想添加一个属性，该属性获取先前的 Department 以及当前的 Department .

In the LINQ query below, I would like to add a property that gets the previous Department as well as the current Department.

下面的LINQ查询返回:

The LINQ query below returns:

EffectiveDate EmployeeID  Department
11/4/2012     10          0000 
1/14/2013     10          9121 
2/2/2016      10          9123 

如何像这样在当前部门旁边显示上一个部门?

How can I show the previous Department next to current Department like this?

EffectiveDate EmployeeID  Department PreviousDepartment
11/4/2012     10          0000       null
1/14/2013     10          9121       0000
2/2/2016      10          9123       9121

这是当前查询

var users = from s in userTable
            where s.EmployeeID == "10"
            group new {s} by new { s.EmployeeID, s.Department} into g
            select new 
            {
                EffectiveDate = g.Max(m => m.s.EffectiveDate), 
                EmployeeID = g.Key.EmployeeID, 
                Department = g.Key.Department
                //PreviousDepartment = ???
            };

推荐答案

一种方法是将数据存储在内存中，然后像这样修改它:

One way to do it is to store the data in memory, and then modify it like this:

var users = from s in userTable
            where s.EmployeeID == "10"
            group new {s} by new { s.EmployeeID, s.Department} into g
            select new MyClass
            {
                EffectiveDate = g.Max(m => m.s.EffectiveDate), 
                EmployeeID = g.Key.EmployeeID, 
                Department = g.Key.Department
                PreviousDepartment = null
            };

var result = users.ToList();

for(int i = 1; i < result.Count; i++)
{
    result[i].PreviousDepartment = result[i-1].Department;
}

请注意，由于匿名类型属性是只读的，因此代码正在生成 MyClass 的新实例，而不是匿名类型.确保使用正确的属性创建此类.

Please note that the code is generating new instances of MyClass instead of an anonymous type since anonymous type properties are read-only. Make sure that you create such class with the correct properties.

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