Question

我正在尝试编写等同于：

的LINQ语句

select e.EmployeeID, EmployeeName = e.FirstName + ' ' + e.LastName
from Employees e
where e.EmployeeID not in
(
    select EmployeeID from Managers
)

我认为我与以下内容非常接近：

from e in Employees
where e.EmployeeID !=    // This is where I'm lost
(
    from m in Managers select m.EmployeeID
)
select new
{
    e.EmployeeID,
    EmployeeName = e.FirstName + ' ' + e.LastName
}

我正在尝试将其放入Html.DropDownList。

Answer 1

我不确定对此的正确查询符号是什么，但以下扩展语法将完成工作

var result = Employees
  .Where( e => !Managers.Where(m => m.EmployeeId == e.EmployeeId).Any())
  .Select( e => new { EmployeeId = e.EmployeeId, EmployeeName = e.FirstName + ' ' + e.LastName);

Answer 2

使用Any：

from e in Employees
where !Managers.Any(m => m.EmployeeID == e.EmployeeID)
select new
{
    e.EmployeeID,
    EmployeeName = e.FirstName + ' ' + e.LastName
}

或者，使用左连接：

from e in Employees
join m in Managers on e.EmployeeID equals m.EmployeeID into managerGroup
from m in managerGroup.DefaultIfEmpty()
where m == null
select new
{
    e.EmployeeID,
    EmployeeName = e.FirstName + ' ' + e.LastName
}

Answer 3

您可以使用fluid implementation of Linq.Except()：

获得所需的结果

List<Employee> employees = new List<Employee>
    {
        new Employee { EmployeeID = 1, FirstName = "John", LastName = "Smith" },
        new Employee { EmployeeID = 2, FirstName = "Jane", LastName = "Doe" },
        new Employee { EmployeeID = 3, FirstName = "Eddie", LastName = "Punchclock" }
    };
List<Employee> managers = new List<Employee>
    {
        new Employee { EmployeeID = 2, FirstName = "Jane", LastName = "Doe" },
    };
var nonManagerEmployees = employees.Except(managers, x => x.EmployeeID)
    .Select(x => new
        {
            x.EmployeeID,
            EmployeeName = x.FirstName + " " + x.LastName
        });

foreach(var entry in nonManagerEmployees)
{
    Console.WriteLine(entry.EmployeeID+" "+entry.EmployeeName);
}

输出：

1 John Smith
3 Eddie Punchclock

Answer 4

使用.Contains（）方法并插入！创建NOT样式语法。

这将是{collection} .Contains（this！= to that）;

您也可能对此感兴趣：http://srtsolutions.com/blogs/billwagner/archive/2006/04/10/linq-samples-part-11.aspx

Answer 5

这是一篇关于在LINQ中使用IN语句的文章。有一点肘部油脂，我相信你可以修改技术来做一个NOT IN。

http://blogs.msdn.com/alexj/archive/2009/03/26/tip-8-writing-where-in-style-queries-using-linq-to-entities.aspx

Linq选择语句 - 不在的地方

5 个答案: