Question

我有两张桌子User＆amp; Employee。

+-------Supervisor----------+
SupervisorId
Password
+---------------------+


+-------Employee----------+
EmployeeId
EmployeeSupervisorId
EmployeeName
+---------------------+

这是我到目前为止所做的事情

SupervisorName = db.Employee.Where(m => m.EmployeeSupervisorId == m.SupervisorId).Select(q => q.EmployeeName).ToList()

我不理解我如何将Employee表连接到自身的概念，以便我可以获得Employee列表及其相应的主管名称

Answer 1

您可以执行以下操作

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Answer 2

SupervisorName  = db.Employee.
                  Join(db.Supervisoer, e => e.EmployeeSupervisorId, s => s.SupervisorId, (e, s) => new { Employee = e, Supervisor = s}.
                  ToList().
                  Select(e => e.EmployeeName).
                  ToList();

Answer 3

您可以使用像这样的简单子查询

var result = db.Employee.Select(e => new
{
    Employee = e,
    SupervisorName = db.Employee
        .Where(s => s.EmployeeId == e.EmployeeSupervisorId)
        .Select(s => s.EmployeeName).FirstOrDefault()        
}).ToList();

Answer 4

请注意，如果您将EmployeeSupervisorId定义为指向EmployeeId的外键，Linq2Sql将自动创建一个EmployeeSupervisor属性（这将是一个Employee对象）

   var list = from e in db.Employee
    //        where e.......  
              select new {
                 Name = e.EmployeeName,
                 Supervisor = e.EmployeeSupervisor.EmployeeName,
    //           otherdetails = e......
                 }

如果尚未定义外键，则必须在查询中明确指定：

   var list = from e in db.Employee
              join s in db.Employee on e.EmployeeSupervisorId equal s.EmployeeId
    //        where e.......  
              select new {
                 Name = e.EmployeeName,
                 Supervisor = s.EmployeeName,
    //           otherdetails = e......
                 }

使用Linq to SQL的表中的自联接或内部查询

4 个答案: