linq2sql加入不在另一个表中的选择数据

Question

请不要使用lamba响应。我发现了类似的线程，但仍然需要帮助。

我试图显示员工表中不是当前选定经理的雇员的名称。

我的两个SQL表的结构是这样，但是这是假的数据

Employees: 
      pk  name  
      1  bob 
      2  sam 
      3  greg 
      4  kip 
      5  jill 
      6  kelly 
      7  chris 


ExpenseTeamMembers: 

      pk  expMgrPk  empPk  
      1   7   2 
      2   7   5 
      3   7   1 
      4   3   6 
      5   3   4 

因此，如果当前选中（经理变量）为3我想所有empPks的名字在雇员表中除对于6，4.（凯利，基普）现在unselectedEmps = sam，jill，bob而不是雇员表中所有其他5个名字。

var unselectedEmps = (from u in db.employees 
         join o in db.expenseTeamMembers on u.pk equals o.empPk 
         where o.expMgrPk != mgr 
         select u.name).ToList(); 

       lstAvailable.DataSource = unselectedEmps; 

Answer 1

我们广泛的讨论之后，我想你想要的是这个。

from u in db.Employees 
where !(from e in db.ExpenseTeamMembers 
     where e.expMgrPk == selectedMgr.pk 
     select e.empPk).Contains(u.pk) 
select u.Name 

Answer 2

的问题是，你正在做内部联接，当你真正需要一个左外连接

见this SO question

Answer 3

我试过以下，它给出了正确的输出。请您尝试一下：

List<Employees> emps = new List<Employees>(); 
     emps.Add(new Employees { PK = 1, Name = "bob" }); 
     emps.Add(new Employees { PK = 2, Name = "sam" }); 
     emps.Add(new Employees { PK = 3, Name = "greg" }); 
     emps.Add(new Employees { PK = 4, Name = "kip" }); 
     emps.Add(new Employees { PK = 5, Name = "jill" }); 
     emps.Add(new Employees { PK = 6, Name = "kelly" }); 
     emps.Add(new Employees { PK = 7, Name = "chris" }); 

     List<ExpenseTeamMembers> etm = new List<ExpenseTeamMembers>(); 
     etm.Add(new ExpenseTeamMembers { empPK = 2, ExpMgrPK = 7, PK = 1 }); 
     etm.Add(new ExpenseTeamMembers { empPK = 5, ExpMgrPK = 7, PK = 2 }); 
     etm.Add(new ExpenseTeamMembers { empPK = 1, ExpMgrPK = 7, PK = 3 }); 
     etm.Add(new ExpenseTeamMembers { empPK = 6, ExpMgrPK = 3, PK = 4 }); 
     etm.Add(new ExpenseTeamMembers { empPK = 4, ExpMgrPK = 3, PK = 5 }); 

     var query = from t in 
         (
          from emp in emps 
          join o in etm on emp.PK equals o.empPK into j 
          from k in j.DefaultIfEmpty() 
          select new { Name = k == null ? string.Empty : emp.Name }) 
        where t.Name != string.Empty 
        select t.Name;