英文:
Pagination in Spring Book JPA with Nested loops
问题
我正在尝试实现分页功能。我有两个表，一个是教师表，另一个是学生表。对于每个教师，都有多个学生。现在我有一个教师姓名的列表，对于每个教师，我都必须找出其所有的学生，并将它们添加到列表中，最后将其返回。我还会得到页码和大小作为输入。
List<StudentDTO> studentDTOList = new ArrayList<>();
List<TeacherEntity> teachers = TeacherRepo.findByName(TeacherNames);
teachers.forEach(teacher -> {
Pageable pageable = PageRequest.of(pageNumber, pageSize); // 使用页码和大小创建分页请求
Page<Student> studentPage = studentRepo.findByTeacherName(teacher, pageable);
List<Student> students = studentPage.getContent(); // 获取当前分页的学生列表
studentDTOList.addAll(students);
});
return studentDTOList;
我知道如果只查询教师库的话如何实现分页功能。但是在存在嵌套查询的情况下，我不太清楚如何实现。
英文:
I am trying to implement Pagination. I am having two tables, a teacher and a student. For each teacher, there are multiple students. Now I got a list of TeacherNames and for each teacher, I have to find all its students and add them to the list, and finally return it. I am getting page number and size also as input.
List<TeacherEntity> teacher = TeacherRepo.findByName(TeacherNames);
Teachers.forEach(teacher - > {
List<Student> students = studentRepo.findByTeacherName(teacher);
studentDTO.addAll(students);
});
return StudentDTO;
I know how to implement pagination if I had to query only in teachersRepo. But I am not able to get how will I do it when there is nesting.
答案1
得分: 1
我假设在学生和教师之间存在@ManyToMany关系。如果没有，请在继续之前创建这种关系。以下是创建关系的示例代码：
public class Teacher {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long teacherId;
//一些字段
@ManyToMany(fetch=FetchType.EAGER,cascade = CascadeType.ALL)
@JoinTable(name = "teacher_student", joinColumns = {
@JoinColumn(name = "teacherId", referencedColumnName = "teacherId") }, inverseJoinColumns = {
@JoinColumn(name = "studentId", referencedColumnName = "studentId") })
@BatchSize(size = 20)
private Set<Student> students = new HashSet<>();
//获取和设置方法
}
现在，在教师存储库中，添加一个方法来在学生和教师之间建立连接：
@Repository
public interface TeacherRepo extends JpaRepository<Teacher, Long> {
@Query(value="SELECT t.teacherName,s.studentName FROM Teacher t left join t.students s")
public ArrayList<User> findByStudent(Pageable paging);
}
在你的服务类中调用这个存储库方法：
public ArrayList<Teacher> findByStudent()
{
// TODO Auto-generated method stub
Pageable paging = PageRequest.of(0, 4);
return teacherRepo.findByStudent(paging);
}
这样你的分页查询将返回4条学生记录。
注意：你可以根据需要添加where条件、分页和排序详细信息。
英文:
I am assuming that you have @ManyToMany relationship between student and teacher. If not, you have to create one before you proceed. Sample code to create relation
public class Teacher
{
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long teacherId;
//some fields
@ManyToMany(fetch=FetchType.EAGER,cascade = CascadeType.ALL)
@JoinTable(name = "teacher_student", joinColumns = {
@JoinColumn(name = "teacherId", referencedColumnName = "techerId") }, inverseJoinColumns = {
@JoinColumn(name = "studentId", referencedColumnName = "studentId") })
@BatchSize(size = 20)
private Set<Stident> students = new HashSet<>();
//Get and set
}
Now, in teacher repo, add a method having join between student and teacher
@Repository
public interface TeacherRepo extends JpaRepository<Teacher, Long>
{
@Query(value="SELECT t.teacherName,s.studentName FROM Teacher t left join t.students s")
public ArrayList<User> findByStudent(Pageable paging);
}
Call this repo method in your sevice class
public ArrayList<Teacher> findByStudent()
{
// TODO Auto-generated method stub
Pageable paging = PageRequest.of(0, 4);
return teacherRepo.findByStudent(paging);
}
This way you pagination will return 4 students records.
Note - You can add where conditions, paginations, sorting details according to your requirement
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