这一章讲的是简单的多对一关系映射。
1.首先是开发环境,使用Maven版本为3.5,jdk版本为9.0.1,Hibernate版本为5.0.1Final,数据库为MySQL5.7.20
2.配置Maven的pom.xml文件,由于我当前的jdk版本以及Hibernate版本所以依赖如配置文件中所列出。
- <?xml version="1.0" encoding="UTF-8"?>
- <project xmlns="http://maven.apache.org/POM/4.0.0"
- xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
- xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
- <modelVersion>4.0.0</modelVersion>
- <groupId>cc.acme_me.hibernate</groupId>
- <artifactId>Hibernate03</artifactId>
- <version>1.0-SNAPSHOT</version>
- <name>Hibernate01</name>
- <dependencies>
- <!-- junit -->
- <dependency>
- <groupId>junit</groupId>
- <artifactId>junit</artifactId>
- <version>4.12</version>
- <scope>test</scope>
- </dependency>
- <!-- mysql-connector-java -->
- <dependency>
- <groupId>mysql</groupId>
- <artifactId>mysql-connector-java</artifactId>
- <version>6.0.6</version>
- </dependency>
- <dependency>
- <groupId>org.hibernate</groupId>
- <artifactId>hibernate-core</artifactId>
- <version>5.2.12.Final</version>
- </dependency>
- <dependency>
- <groupId>antlr</groupId>
- <artifactId>antlr</artifactId>
- <version>2.7.7</version>
- </dependency>
- <dependency>
- <groupId>com.fasterxml</groupId>
- <artifactId>classmate</artifactId>
- <version>1.3.4</version>
- </dependency>
- <dependency>
- <groupId>dom4j</groupId>
- <artifactId>dom4j</artifactId>
- <version>1.6.1</version>
- </dependency>
- <dependency>
- <groupId>org.hibernate.common</groupId>
- <artifactId>hibernate-commons-annotations</artifactId>
- <version>5.0.1.Final</version>
- </dependency>
- <dependency>
- <groupId>org.jboss.logging</groupId>
- <artifactId>jboss-logging</artifactId>
- <version>3.3.0.Final</version>
- </dependency>
- <dependency>
- <groupId>org.hibernate.javax.persistence</groupId>
- <artifactId>hibernate-jpa-2.1-api</artifactId>
- <version>1.0.0.Final</version>
- </dependency>
- <dependency>
- <groupId>org.javassist</groupId>
- <artifactId>javassist</artifactId>
- <version>3.20.0-GA</version>
- </dependency>
- <dependency>
- <groupId>org.jboss</groupId>
- <artifactId>jandex</artifactId>
- <version>2.0.3.Final</version>
- </dependency>
- <dependency>
- <groupId>org.jboss.logging</groupId>
- <artifactId>jboss-logging</artifactId>
- <version>3.3.0.Final</version>
- </dependency>
- <dependency>
- <groupId>org.jboss.spec.javax.transaction</groupId>
- <artifactId>jboss-transaction-api_1.2_spec</artifactId>
- <version>1.0.1.Final</version>
- </dependency>
- <dependency>
- <groupId>com.sun.xml.bind</groupId>
- <artifactId>jaxb-core</artifactId>
- <version>2.3.0</version>
- </dependency>
- <dependency>
- <groupId>javax.xml.bind</groupId>
- <artifactId>jaxb-api</artifactId>
- <version>2.3.0</version>
- </dependency>
- <dependency>
- <groupId>com.sun.xml.bind</groupId>
- <artifactId>jaxb-impl</artifactId>
- <version>2.3.0</version>
- </dependency>
- <dependency>
- <groupId>javax.activation</groupId>
- <artifactId>activation</artifactId>
- <version>1.1.1</version>
- </dependency>
- </dependencies>
- </project>
3.Hibernate的全局配置文件hibernate.cfg.xml,这一章我们同样还是使用注解
- <?xml version="1.0" encoding="UTF-8"?>
- <!DOCTYPE hibernate-configuration PUBLIC
- "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
- "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
- <hibernate-configuration>
- <session-factory>
- <!--数据库连接设置-->
- <property name="connection.username">root</property>
- <property name="connection.password">root</property>
- <property name="connection.url">jdbc:mysql://localhost:3306/db_hibernate</property>
- <property name="connection.driver_class">com.mysql.cj.jdbc.Driver</property>
- <!--数据库方言-->
- <property name="dialect">org.hibernate.dialect.MySQL57Dialect</property>
- <!--显示sql语句-->
- <property name="show_sql">true</property>
- <!--格式化sql语句-->
- <property name="format_sql">true</property>
- <!--设置ddl 根据设置自动更新表结构 包括添加删除表 更新表结构-->
- <property name="hbm2ddl.auto">create-drop</property>
- <!--告诉Hibernate映射的实体类-->
- <mapping class="cc.acme_me.model.Student"/>
- <mapping class="cc.acme_me.model.Group"/>
- </session-factory>
- </hibernate-configuration>
4.新建两个实体类Student和Group并且表示一对多的关系
- package cc.acme_me.model;
- import org.hibernate.annotations.GenericGenerator;
- import javax.persistence.*;
- @Entity
- @Table(name = "t_group")
- public class Group {
- @Column(name = "groupID")
- @Id
- @GenericGenerator(name = "native", strategy = "native")//定义策略然后下面使用
- @GeneratedValue(generator = "native")
- private int groupID;//组ID
- @Column(name = "groupName")
- private String groupName;//组名
- public String getGroupName() {
- return groupName;
- }
- public void setGroupName(String groupName) {
- this.groupName = groupName;
- }
- public int getGroupID() {
- return groupID;
- }
- public void setGroupID(int groupID) {
- this.groupID = groupID;
- }
- @Override
- public String toString() {
- return "Group{" +
- "groupID=" + groupID +
- ", groupName='" + groupName + '\'' +
- '}';
- }
- }
通常,我们在一对多的关系中,在多的一方增加少的一方的关联关系。
这也是这一章所讲到的注解@ManyToOne和@JoinColumn,当然,这两个注解还有属性,我在后续的章节中慢慢增加。JoinColumn的name属性便是外键的列名
- package cc.acme_me.model;
- import org.hibernate.annotations.GenericGenerator;
- import javax.persistence.*;
- @Entity
- @Table(name = "t_student")
- public class Student {
- @Id
- @GenericGenerator(name = "native", strategy = "native")
- @GeneratedValue(generator = "native")
- private long id;//作为主键
- @Column(name = "studentname")
- private String name;//姓名
- @Column(name = "studentage")
- private int age;//年龄
- @ManyToOne
- @JoinColumn(name = "groupID")
- private Group group;//所属组
- 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 int getAge() {
- return age;
- }
- public void setAge(int age) {
- this.age = age;
- }
- public Group getGroup() {
- return group;
- }
- public void setGroup(Group group) {
- this.group = group;
- }
- @Override
- public String toString() {
- return "Student{" +
- "id=" + id +
- ", name='" + name + '\'' +
- ", age=" + age +
- ", group=" + group +
- '}';
- }
- }
5.接下来便是使用Junit测试进行测试
首先贴上工具类(其实是偷懒)
- package cc.acme_me.utils;
- import org.hibernate.Session;
- import org.hibernate.SessionFactory;
- import org.hibernate.boot.MetadataSources;
- import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
- import org.hibernate.service.ServiceRegistry;
- public class SessionUtils {
- public static Session openSession() {
- ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().configure().build();
- SessionFactory sessionFactory = new MetadataSources(serviceRegistry).buildMetadata().buildSessionFactory();
- return sessionFactory.openSession();
- }
- }
测试类
- package cc.acme_me.test;
- import cc.acme_me.model.Group;
- import cc.acme_me.model.Student;
- import cc.acme_me.utils.SessionUtils;
- import org.hibernate.Session;
- import org.junit.After;
- import org.junit.Before;
- import org.junit.Test;
- public class TestStudent {
- private Session session = null;
- @Before
- public void openSession() {
- session = SessionUtils.openSession();
- session.beginTransaction();
- }
- @After
- public void closeSession() {
- session.getTransaction().commit();
- session.close();
- }
- @Test
- public void testAdd() {
- //创建组并保存
- Group group = new Group();
- group.setGroupName("Group 1");
- session.save(group);//因为没有配置cascade,所以需要手动保存一下组
- //组里面添加一个学生
- Student student = new Student();
- student.setAge(18);
- student.setName("Admin");
- student.setGroup(group);
- session.save(student);
- //组里面再添加一个学生
- student = new Student();
- student.setName("Admin2");
- student.setAge(20);
- session.save(student);
- student.setGroup(group);
- session.save(student);
- }
- }
首先是添加方法,同时也看看Hibernate打印出来的sql语句。
- Hibernate:
- insert
- into
- t_group
- (groupName)
- values
- (?)
- Hibernate:
- insert
- into
- t_student
- (studentage, groupID, studentname)
- values
- (?, ?, ?)
- Hibernate:
- insert
- into
- t_student
- (studentage, groupID, studentname)
- values
- (?, ?, ?)
- Hibernate:
- update
- t_student
- set
- studentage=?,
- groupID=?,
- studentname=?
- where
- id=?
插入成功后我们也可以在表中查看到刚刚插入的数据,同时也可以查看一下表的结构。
当然,也可以使用show create table 'tb_name'来查看表创建的语句。
上面展示了表内的数据,接着就试试查询。
- @Test
- public void testFind() {
- Student student = session.get(Student.class, 1L);
- System.out.println(student);
- }
可以看到控制台的sql语句滚动以及打印出来的student信息。
而且同样也可以查询Group的内容。
- @Test
- public void testFindGroup() {
- Group group = session.get(Group.class, 1);
- System.out.println(group);
- }
接下来的update和delete便不再一一列出,因为这并没有什么意思。
我这个时候对Group操作,我要删除它。但是Group的主键是Student的外键,删除时Group的时候Hibernate会如何出来Student表内的数据?是将外键值置为为空(0)?还是同事删除Group内的Student的数据?
- @Test
- public void testDeleteGroup() {
- Group group = session.get(Group.class, 1);
- session.delete(group);
- }
执行这个操作,结局红红的异常,并且,异常会明确的告诉你:java.sql.SQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`db_hibernate`.`t_student`, CONSTRAINT `FKeyqu03o2m70hvm5iymc7cj5kd` FOREIGN KEY (`groupID`) REFERENCES `t_group` (`groupID`))
这个时候肯定有人想说,我就是想要干掉Student内的数据,级联操作,全部给我干。
这个就放到后面去配置cascade来实现。