Question

var qry = from _Cr in _er.Courses 
          from _R in _er.ResultsHeaders  
          where  _R.Studentid == studentid 
          && !_Cr.CourseID.Contains( _R.CourseID )
          select new Obj_getCourses
          {
              Courseid = _Cr.CourseID,
              CourseName = _Cr.CourseName 
          };

_er.CoursesTable中有4个值，_er.ResultsHeader表为空。我期待查询中的4个值，但查询没有返回任何值。这是我试图在LINQ中编写的查询。

Select * \
from Courses \
where courseid not in (Select courseid from ResultsHeader where studentid = 123);

帮助要求。

提前致谢

Answer 1

要获取您发布的SQL，您应该尝试以下查询：

var qry = from _Cr in _er.Courses 
          where !_er.ResultsHeader.Where(r => r.StudentId == studentId)
                                  .Select(r => r.CourseID)
                                  .Contains(_Cr.CourseID)
          select new Obj_getCourses
          {
              Courseid = _Cr.CourseID,
              CourseName = _Cr.CourseName 
          };

Answer 2

这可以为您提供所需的结果。我用C＃语句风格编写它，所以希望它具有LINQ风格并不是先决条件......

var qry = _er.Courses
    .Where( c => !c.CourseID.Contains(_er.ResultsHeader
        .Where( r => r.StudentID == 123)
        .Select(r => r.CourseID)
    )
    .Select(c => new Obj_getCourses 
    {
        Courseid = c.CourseID,
        Coursename = c.CourseName
    });

带有包含空值的Linq查询

2 个答案: