Hibernate:示例查询和多对一创建列表

基础概念

Hibernate 是一个开源的 Java ORM（对象关系映射）框架，它允许开发者将 Java 对象与数据库表进行映射，从而简化数据库操作。Hibernate 提供了 HQL（Hibernate Query Language）和 Criteria API 来执行查询操作。

示例查询

假设我们有两个实体类 Student 和 Classroom，它们之间是多对一的关系，即多个学生属于一个教室。

@Entity
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    @ManyToOne
    @JoinColumn(name = "classroom_id")
    private Classroom classroom;

    // getters and setters
}

@Entity
public class Classroom {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    @OneToMany(mappedBy = "classroom")
    private List<Student> students;

    // getters and getters
}

我们可以使用 HQL 或 Criteria API 来查询数据。以下是使用 HQL 的示例：

Session session = sessionFactory.openSession();
String hql = "FROM Student s JOIN FETCH s.classroom WHERE s.name = :studentName";
Query<Student> query = session.createQuery(hql, Student.class);
query.setParameter("studentName", "John Doe");
List<Student> students = query.getResultList();
session.close();

多对一创建列表

假设我们要创建一个包含多个学生的列表，并将这些学生分配到一个教室中。

Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();

Classroom classroom = new Classroom();
classroom.setName("Room 101");

Student student1 = new Student();
student1.setName("John Doe");
student1.setClassroom(classroom);

Student student2 = new Student();
student2.setName("Jane Doe");
student2.setClassroom(classroom);

List<Student> students = new ArrayList<>();
students.add(student1);
students.add(student2);

for (Student student : students) {
    session.save(student);
}

tx.commit();
session.close();