linq2sql联接选择不在另一个表中的数据

Question

请不要使用lamba进行回复。 我发现了类似的线程，但仍需要帮助。

我试图显示不属于当前选定经理雇员的雇员表中的姓名。

我的两个sql表的结构是这样的，但这是假数据

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，如果当前选择的（mgr变量）为3，我想获取employees表中除6、4之外的所有empPks的名称。（kelly，kip）现在unselectedEmps = sam，jill，bob，而不是全部的5员工表中的其他名称。

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

问题是您实际上需要左外部连接时正在进行内部连接

看到这个问题

Answer 2

经过我们的广泛讨论，我认为您想要的是这个。

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 3

我尝试了以下方法，它给出了正确的输出。 请尝试：

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;