acme
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。