如何将 SQL 转换为 lambda 表达式

Question

在我的数据库中，我创建了如下表结构。

CREATE TABLE Course 
(
    Course_ID int IDENTITY(1,1) PRIMARY KEY,
    Name varchar(255) NOT NULL,
);

CREATE TABLE Student 
(
    Stu_ID int IDENTITY(1,1) PRIMARY KEY,
    Name varchar(255) NOT NULL,
    Mobile varchar(255),
    Age int,
    Course_ID int,
    FOREIGN KEY (Course_ID) REFERENCES Course(Course_ID)
);

CREATE TABLE Subject  
(
    Sub_ID int IDENTITY(1,1) PRIMARY KEY,
    Name varchar(255) NOT NULL,
);

CREATE TABLE Teacher 
(
    Teach_ID int IDENTITY(1,1) PRIMARY KEY,
    Name varchar(255) NOT NULL,
    Mobile varchar(255)
);

CREATE TABLE Course_Subject 
(
    CouSub_ID int IDENTITY(1,1) PRIMARY KEY,
    Course_ID int,
    Sub_ID int,
    FOREIGN KEY (Course_ID) REFERENCES Course(Course_ID),
    FOREIGN KEY (Sub_ID) REFERENCES Subject(Sub_ID)
);

CREATE TABLE Teacher_Subject 
(
    TeachSub_ID int IDENTITY(1,1) PRIMARY KEY,
    Teach_ID int,
    Sub_ID int,
    FOREIGN KEY (Teach_ID) REFERENCES Teacher(Teach_ID),
    FOREIGN KEY (Sub_ID) REFERENCES Subject(Sub_ID)
);

现在我的问题是我需要检索向某位老师学习的学生数据，这意味着需要检索一些向 his/her 学习的老师的学生。来完成我的要求。我写了这个 SQL 查询。

select 
    s.*
from 
    tbl_student s
inner join 
    Course_Subject tcs on s.Course_Id = tcs.Course_Id
inner join 
    Teacher_Subject tst on tst.Sub_ID = tcs.Sub_ID
inner join 
    Teacher t on t.Teach_ID = tst.Teach_ID
where 
    t.Teach_ID = @SomeTeacherId

现在我需要将此查询转换为 lambda 表达式或 Linq。我该怎么做？请帮我。有任何可能的方法来使用 Visual Studio.

生成它

Answer 1

好吧，您可以使用 EF 生成到表的对象映射。并使用 LINQ 以稍微不同的语法重写您的查询：

var result = from students in tbl_student
             join subjects in Course_Subject on students.Course_Id == subjects.Course_Id
             join ts in Teacher_Subject on subjects.Sub_ID == ts.Sub_ID
             join teachers in Teacher on teachers.Teach_ID == ts.Teach_ID
             where teachers.Teach_ID == "your_value"
             select students;

不确定这是一个绝对正确的查询，但我希望你能理解主要思想。

Answer 2

Have any possible way to generate this using Visual Studio.?

是的，您可以使用 Linq-to-SQL

对于您的查询，这可能是合适的

var students = from student in db.Students
            join tcs in db.CourseSubjects on student.CourseId equals tcs.CourseId
            join tst in db.TeacherSubjects on tcs.SubId equals tst.SubId
            join t in db.Teachers on tst.TeachId equals t.TeachId
            where t.TeachId == someTeacherId
            select student;

Answer 3

拉姆达：

Students
.Where(x=> x.Course.Course_Subjects
        .Any(y => y.Subject.Teacher_Subjects
                .Any(z => z.Teach_ID == someTeacherId)
        )
)
.Select(x => x)

如何将 SQL 转换为 lambda 表达式

How can I convert SQL to lambda expressions

c#

linq

sql-server

lambda

linq-to-sql