将 SQL 查询转换为 Linq 表达式

Question

There are tables Subject , Student and SubjectEnrolled

• Subject table have two columns SubjectId and SubjectName
• SubjectEnrolled table also have two column StudentID (foreign key to StudentTable ) and SubjectId (foreign key to Subject )

I want to convert this SQL query

SELECT SubjectName
FROM Subject
WHERE SubjectId IN 
(
    SELECT SubjectId
    FROM SubjectEnrolled
    WHERE StudentID=7
)

Into a Linq or Lamda expression

using (var db = new DbContext())
{
    var res = from  r in db.Subjects.....
}

Answer 1

1 - SQL: use inner join instead IN :

SELECT SubjectName FROM Subject sub
INNER JOIN SubjectEnrolled subEn on sub.SubjectId = subEn.SubjectId
WHERE subEn.StudentID = 7

2 - Linq Query Join :

var res = (from sub in db.Subjects
          join subEn in db.SubjectEnrolleds on sub.SubjectId equals subEn.SubjectId
          where subEn.StudentID = 7).ToList();

I hope you find this helpful.