Question

tl; dr version：我需要这个sql语句来使用linq到EF

这是SQL中的查询：

select 
stu.SyStudentId, 
rtrim(stu.StuNum) as StudentNumber, 
stu.SSN,
stu.FirstName, 
stu.LastName, 
Email, 
OtherEmail, 
stu.StartDate,
case 
when (systa.category = 'E') then 'Enrolled'  
    when (systa.category = 'A') then 'Active'  
    else 'This should never happen'
end as StatusCategory,
rtrim(schsta.Code) as SchoolStatusCode,
pic.StudentPicture,
case when (stu.DateLstMod > isnull(pic.DateLstMod,'1900-1-1')) 
then stu.DateLstMod 
    else pic.DateLstMod 
end as DateLstMod
from 
SyStudent stu
inner join syschoolstatus schsta on schsta.syschoolstatusid = stu.syschoolstatusid
inner join SyStatus systa on systa.SyStatusId = schsta.SyStatusId
left outer join cmstudentpicture pic on pic.systudentid = stu.systudentid
where stu.sycampusid = 6
and systa.category in ('E','A')

丑陋的查询，继承自旧系统..

我正在努力获得一些利用实体框架的服务。我试图使用基于方法的语法使此查询工作。我首先得到了我要加入的所有对象的列表：

var students = ctx.syStudents.ToList(); //root
var statusCode = ctx.SySchoolStatus.ToList(); //inner
var status = ctx.syStatus.ToList(); //inner
var picture = ctx.CmStudentPictures.ToList(); //left outer

'ctx'是我的dbcontext类。

我到目前为止的查询是：

var query = students
   .GroupJoin(statusCode,
   student => student.SySchoolStatusID,
   statuscode => statuscode.SySchoolStatusID,
   (student, studentStatusCode) => new
   {
      StudentName = student.FirstName
   });

显然没有完全实现，但我想知道这是否是执行此操作的最佳方式，因为我将有几个内连接，然后是左外连接，或者是否有更好的，更可读的方法来完成这项工作？

Answer 1

我肯定会建议使用lambda语法进行连接的查询语法。

尝试以下几点：

var result = 
from stu in SyStudent
join schsta in syschoolstatus on stu.syschoolstatusid equals schsta.syschoolstatusid //inner
join systa in SyStatus on schsta.SyStatusId equals systa.SyStatusId //innner
from pic in cmstudentpicture.Where(x => x.systudentid = stu.systudentid).DefaultIfEmpty() //outer 
where stu.sycampusid = 6
select new{
    stu,
    schsta,
    systa,
    pic
};

无法弄清楚如何在linq到EF中进行多个连接

1 个答案: