整理笔记---Hibernate的xml与Annotation配置映射关系

有三个java类,分别用Hibernate的xml配置方法和Annotation注解方法实现这三个类之间的映射关系



- 班级和专业之间（一对多）

- 专业和班级之间（多对一）

- 学生和班级之间（多对一）

- 班级和学生之间（一对多）

Hibernate的Annotation方法

ClassRoom.java

package com.xing.hibernate_hql_annotation.entity;

import javax.persistence.*;
import java.util.Set;

/**
* Created by Administrator on 2016/8/3.
* 班级
*/
@Entity
@Table(name = "t_class_room")
public class ClassRoom {
private int id;
private String name ;
private int grade ;
//班级和学生：一对多关系
private Set<Student> stus;
//班级和专业：多对一关系
private Special sepcial ;

@Id
@GeneratedValue
public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getGrade() {
return grade;
}

public void setGrade(int grade) {
this.grade = grade;
}

@OneToMany(mappedBy = "classRoom")
public Set<Student> getStus() {
return stus;
}

public void setStus(Set<Student> stus) {
this.stus = stus;
}
@ManyToOne
@JoinColumn(name = "cid")
public Special getSepcial() {
return sepcial;
}

public void setSepcial(Special sepcial) {
this.sepcial = sepcial;
}
}

Special.java

package com.xing.hibernate_hql_annotation.entity;

import javax.persistence.*;
import java.util.Set;

/**
* Created by Administrator on 2016/8/3.
* 专业
*/
@Entity
@Table(name = "t_sepcial")
public class Special {
private int id;
private String name ;
private String  type;
private Set<ClassRoom> classRooms ;

@Id
@GeneratedValue
public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getType() {
return type;
}

public void setType(String type) {
this.type = type;
}
// 当前对象在对应ClassRoom对象的属性名，它来维护关系
@OneToMany(mappedBy = "sepcial")
public Set<ClassRoom> getClassRooms() {
return classRooms;
}

public void setClassRooms(Set<ClassRoom> classRooms) {
this.classRooms = classRooms;
}
}

Student.java

package com.xing.hibernate_hql_annotation.entity;

import javax.persistence.*;

/**
* Created by Administrator on 2016/8/3.
* 学生
*/
@Entity
@Table(name = "t_stu")
public class Student {
private int id;
private String name;
private String sex ;
//学生和班级（多对一）
private ClassRoom classRoom ;

@Id
@GeneratedValue
public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getSex() {
return sex;
}

public void setSex(String sex) {
this.sex = sex;
}
//设置数据库表中对应的关联的外键名称
@ManyToOne
@JoinColumn(name = "cid")
public ClassRoom getClassRoom() {
return classRoom;
}

public void setClassRoom(ClassRoom classRoom) {
this.classRoom = classRoom;
}
}

hibernate.cfg.xml

<!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>
<!-- 配置数据库方言 -->
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<!-- 配置数据库连接驱动-->
<property name="hibernate.connection.driver_class" >com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://127.0.0.1:3306/test</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">root</property>
<!-- 配置打印sql -->
<property name="show_sql">true</property>
<!-- 配置  自动完成类到数据表的转换-->
<property name="hibernate.hbm2ddl.auto">update</property>
<!-- 加入实体类的映射文件-->
<mapping class="com.xing.hibernate_hql_annotation.entity.Special"></mapping>
<mapping class="com.xing.hibernate_hql_annotation.entity.Student"></mapping>
<mapping class="com.xing.hibernate_hql_annotation.entity.ClassRoom"></mapping>

</session-factory>
</hibernate-configuration>

Hibernate利用xml配置文件来实现关系映射

ClassRoom.java

package com.xing.hibernate_hql_xml.entity;

import java.util.Set;

/**
* Created by Administrator on 2016/8/3.
*/
public class ClassRoom {
private int id;
private String name;
private int grade;

private Set<Student> stus;

private Special special;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getGrade() {
return grade;
}

public void setGrade(int grade) {
this.grade = grade;
}

public Set<Student> getStus() {
return stus;
}

public void setStus(Set<Student> stus) {
this.stus = stus;
}

public Special getSpecial() {
return special;
}

public void setSpecial(Special special) {
this.special = special;
}
}

Special.java

package com.xing.hibernate_hql_xml.entity;

/**
* Created by Administrator on 2016/8/3.
*/
public class Special {
private int id;
private String name ;
private String  type;
private ClassRoom classRoom ;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getType() {
return type;
}

public void setType(String type) {
this.type = type;
}

public ClassRoom getClassRoom() {
return classRoom;
}

public void setClassRoom(ClassRoom classRoom) {
this.classRoom = classRoom;
}
}

Student.java

package com.xing.hibernate_hql_xml.entity;

/**
* Created by Administrator on 2016/8/3.
*/
public class Student {
private int id;
private String name;
private String sex ;

private ClassRoom classRoom ;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getSex() {
return sex;
}

public void setSex(String sex) {
this.sex = sex;
}

public ClassRoom getClassRoom() {
return classRoom;
}

public void setClassRoom(ClassRoom classRoom) {
this.classRoom = classRoom;
}
}

ClassRoom.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- Generated Nov 9, 2006 6:27:53 PM by Hibernate Tools 3.2.0.beta7 -->
<hibernate-mapping package="com.xing.hibernate_hql_xml.entity">
<class name="ClassRoom" table="t_class_room" >
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<property name="grade"/>
<many-to-one name="special" column="sp_id" />
<set name="stus" inverse="true" lazy="extra">
<key column="cid"></key>
<one-to-many class="Student" />
</set>
</class>
</hibernate-mapping>

Specail.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- Generated Nov 9, 2006 6:27:53 PM by Hibernate Tools 3.2.0.beta7 -->
<hibernate-mapping package="com.xing.hibernate_hql_xml.entity">
<class name="com.xing.hibernate_hql_xml.entity.Special" table="t_special" >
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<property name="type"/>
<set name="classRoom" inverse="true" lazy="extra">
<key column="sp_id"></key>
<one-to-many class="ClassRoom"></one-to-many>
</set>
</class>
</hibernate-mapping>

Student.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- Generated Nov 9, 2006 6:27:53 PM by Hibernate Tools 3.2.0.beta7 -->
<hibernate-mapping package="com.xing.hibernate_hql_xml.entity">
<class name="Student" table="t_student" >
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<property name="sex"/>
<many-to-one name="classRoom"  column="cid"/>
</class>
</hibernate-mapping>

两种方法用下面测试代码测试运行，如果能生成下面三张表，则说明配置成功了

import com.xing.util.HibernateUtil;
import org.hibernate.Session;
import org.junit.Test;

/**
* Created by Administrator on 2016/8/3.
*/

public class TestHql {
@Test
public void test01(){

Session session = null ;

try {
session = HibernateUtil.openSession() ;

session.beginTransaction() ;

session.getTransaction().commit();
} catch (Exception e) {
e.printStackTrace();
if(session!=null) session.getTransaction().rollback();
} finally {
HibernateUtil.closeSession(session);
}

}
}

小记：

1. 在做映射关系的时候尽可能使用单向关联

2. 在大项目中（数据量超多）如果使用hibernate不建议使用对象关联，可以用冗余字段来代替外键。（但是修改的时候要考虑）