C# 不在第二条中列出对象

我正在尝试创建如下查询：

select * from Subjects
where subjectid not in ( select subjectid from results)

 _CD.Where(c => !_results.Select(r => r.subjectid).Contains(c.subjectid))

为此，我有一个对象查询结果表

 var _results = 
     new List<C_MiscObjects.obj_Results>();
 _results = _Enrollment.GetResultView(Convert.ToInt16(lblSid.Text), lblCourseid.Text);

SQL:

林克：

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你想要这样的东西：

select * from Subjects
where subjectid not in ( select subjectid from results)

 _CD.Where(c => !_results.Select(r => r.subjectid).Contains(c.subjectid))

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SQL查询本身可以根据两个表之间的左联接进行重写，如下所示：

select * from subjects s
left join results r on s.subjectid = r.subjectid
where r.subjectid is null

翻译成LINQ后，它变成：

var filtered = _CD
            .GroupJoin(_results, x => x.subjectid, y => y.subjectid, (x,y) => new {x,y})
            .SelectMany(xy => xy.y.DefaultIfEmpty(), (x,y) => new {x,y})
            .Where(xy => xy.y == null)
            .Select(xy => xy.x);

可能会有帮助。您可以尝试_CD=\u Enrollment.GetSubjectslblCourseid.Text.Where=>_results.Anyr=>r.subjectid==s.subjectid

select * from subjects s
left join results r on s.subjectid = r.subjectid
where r.subjectid is null

var filtered = _CD
            .GroupJoin(_results, x => x.subjectid, y => y.subjectid, (x,y) => new {x,y})
            .SelectMany(xy => xy.y.DefaultIfEmpty(), (x,y) => new {x,y})
            .Where(xy => xy.y == null)
            .Select(xy => xy.x);