Hibernate的多表联合查询
在Hibernate中，多表联合查询（Join Query）用于从多个相关表中提取数据。通过使用HQL（Hibernate Query Language）或Criteria API，可以实现不同表之间的联接查询。
使用HQL进行多表联合查询的示例代码
首先，假设我们有两个实体类：Student 和 Course，并且它们之间存在多对多的关系。
实体类定义
Student 类
java
package com.example.domain;
import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;
@Entity
@Table(name = "student")
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(name = "name")
private String name;
@ManyToMany(cascade = { CascadeType.ALL })
@JoinTable(
name = "student_course",
joinColumns = { @JoinColumn(name = "student_id") },
inverseJoinColumns = { @JoinColumn(name = "course_id") }
)
private Set<Course> courses = new HashSet<>();
public Student() {}
public Student(String name) {
this.name = name;
}
// Getters 和 Setters
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<Course> getCourses() {
return courses;
}
public void setCourses(Set<Course> courses) {
this.courses = courses;
}
}Course 类
java
package com.example.domain;
import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;
@Entity
@Table(name = "course")
public class Course {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(name = "name")
private String name;
@ManyToMany(mappedBy = "courses")
private Set<Student> students = new HashSet<>();
public Course() {}
public Course(String name) {
this.name = name;
}
// Getters 和 Setters
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<Student> getStudents() {
return students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}
}Hibernate配置文件 hibernate.cfg.xml
xml
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- 数据库连接配置 -->
<property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/your_database</property>
<property name="hibernate.connection.username">your_username</property>
<property name="hibernate.connection.password">your_password</property>
<!-- Hibernate 属性配置 -->
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hibernate.show_sql">true</property>
<property name="hibernate.format_sql">true</property>
<property name="hibernate.hbm2ddl.auto">update</property>
<!-- 映射类 -->
<mapping class="com.example.domain.Student"/>
<mapping class="com.example.domain.Course"/>
</session-factory>
</hibernate-configuration>HibernateUtil类
java
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtil {
private static final SessionFactory sessionFactory;
static {
try {
// 从配置文件创建SessionFactory
sessionFactory = new Configuration().configure("hibernate.cfg.xml").buildSessionFactory();
} catch (Throwable ex) {
// 记录启动失败的错误
System.err.println("Initial SessionFactory creation failed." + ex);
throw new ExceptionInInitializerError(ex);
}
}
public static SessionFactory getSessionFactory() {
return sessionFactory;
}
}使用HQL进行多表联合查询
插入示例数据
java
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
public class HibernateInsertData {
public static void main(String[] args) {
// 获取SessionFactory
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
// 插入示例数据
insertSampleData(sessionFactory);
// 关闭SessionFactory
sessionFactory.close();
}
private static void insertSampleData(SessionFactory sessionFactory) {
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
try {
// 创建学生
Student student1 = new Student("John Doe");
Student student2 = new Student("Jane Doe");
// 创建课程
Course course1 = new Course("Mathematics");
Course course2 = new Course("History");
// 建立多对多关系
student1.getCourses().add(course1);
student1.getCourses().add(course2);
student2.getCourses().add(course1);
student2.getCourses().add(course2);
course1.getStudents().add(student1);
course1.getStudents().add(student2);
course2.getStudents().add(student1);
course2.getStudents().add(student2);
// 保存数据
session.save(student1);
session.save(student2);
transaction.commit();
System.out.println("Inserted sample data");
} catch (Exception e) {
if (transaction != null) {
transaction.rollback();
}
e.printStackTrace();
} finally {
if (session != null) {
session.close();
}
}
}
}HQL联合查询示例
查询所有学生及其选修的课程
java
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.query.Query;
import java.util.List;
public class HibernateHQLJoinQueryExample {
public static void main(String[] args) {
// 获取SessionFactory
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
// 使用HQL进行联合查询
queryStudentCourses(sessionFactory);
// 关闭SessionFactory
sessionFactory.close();
}
private static void queryStudentCourses(SessionFactory sessionFactory) {
Session session = sessionFactory.openSession();
try {
String hql = "SELECT s.name, c.name FROM Student s JOIN s.courses c";
Query<Object[]> query = session.createQuery(hql, Object[].class);
List<Object[]> results = query.list();
System.out.println("Student and their Courses:");
for (Object[] row : results) {
String studentName = (String) row[0];
String courseName = (String) row[1];
System.out.println("Student: " + studentName + ", Course: " + courseName);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (session != null) {
session.close();
}
}
}
}使用Criteria API进行多表联合查询
Criteria API联合查询示例
查询所有学生及其选修的课程
java
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Join;
import javax.persistence.criteria.Root;
import java.util.List;
public class HibernateCriteriaJoinQueryExample {
public static void main(String[] args) {
// 获取SessionFactory
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
// 使用Criteria API进行联合查询
queryStudentCourses(sessionFactory);
// 关闭SessionFactory
sessionFactory.close();
}
private static void queryStudentCourses(SessionFactory sessionFactory) {
Session session = sessionFactory.openSession();
try {
CriteriaBuilder criteriaBuilder = session.getCriteriaBuilder();
CriteriaQuery<Object[]> criteriaQuery = criteriaBuilder.createQuery(Object[].class);
Root<Student> studentRoot = criteriaQuery.from(Student.class);
Join<Student, Course> courseJoin = studentRoot.join("courses");
criteriaQuery.multiselect(studentRoot.get("name"), courseJoin.get("name"));
List<Object[]> results = session.createQuery(criteriaQuery).getResultList();
System.out.println("Student and their Courses:");
for (Object[] row : results) {
String studentName = (String) row[0];
String courseName = (String) row[1];
System.out.println("Student: " + studentName + ", Course: " + courseName);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (session != null) {
session.close();
}
}
}
}详细解释
- 实体类定义 ：
Student类和Course类通过@ManyToMany注解来定义多对多的关系。Student类使用@JoinTable注解来定义中间表，指定了关联的学生和课程的外键。