一、单向一对多（）
- 案例一（用XML文件配置）： 一个班级有多个学生，班级可以查看所有学生的信息。
- ClassBean.java
package bean; import java.util.HashSet;
import java.util.Set; /**
* ClassBean entity. @author MyEclipse Persistence Tools
*/ public class ClassBean implements java.io.Serializable { // Fields private Integer classid;
private String classname; private Set<StudentBean> stuSet=new HashSet<StudentBean>(); // Constructors /** default constructor */
public ClassBean() {
} /** minimal constructor */
public ClassBean(Integer classid) {
this.classid = classid;
} /** full constructor */
public ClassBean(Integer classid, String classname) {
this.classid = classid;
this.classname = classname;
} // Property accessors public Integer getClassid() {
return this.classid;
} public void setClassid(Integer classid) {
this.classid = classid;
} public String getClassname() {
return this.classname;
} public void setClassname(String classname) {
this.classname = classname;
} public Set<StudentBean> getStuSet() {
return stuSet;
} public void setStuSet(Set<StudentBean> stuSet) {
this.stuSet = stuSet;
} }
StudentBean.java
package bean; /**
* StudentBean entity. @author MyEclipse Persistence Tools
*/ public class StudentBean implements java.io.Serializable { // Fields private Integer stuid;
private String stuname;
private Integer classId; // Constructors /** default constructor */
public StudentBean() {
} /** minimal constructor */
public StudentBean(Integer stuid) {
this.stuid = stuid;
} /** full constructor */
public StudentBean(Integer stuid, String stuname, Integer classId) {
this.stuid = stuid;
this.stuname = stuname;
this.classId = classId;
} // Property accessors public Integer getStuid() {
return this.stuid;
} public void setStuid(Integer stuid) {
this.stuid = stuid;
} public String getStuname() {
return this.stuname;
} public void setStuname(String stuname) {
this.stuname = stuname;
} public Integer getClassId() {
return this.classId;
} public void setClassId(Integer classId) {
this.classId = classId;
} }
- 单向一对多的映射文件 ：
ClassBean.hbm.xml
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!--
Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
<class name="bean.ClassBean" table="t_class" catalog="test">
<id name="classid" type="java.lang.Integer">
<column name="classid" />
<generator class="assigned"></generator>
</id>
<property name="classname" type="java.lang.String">
<column name="classname" />
</property> <!--set元素，就是定义一个集合，它的name属性值是对应的POJO中的相关属性名称-->
<set name="stuSet" cascade="all">
<key column="class_id"></key> <!--指定“多”的一段的外键，与“一”端得主键相关联，这里的column=“class_id”是指数据库中的字段，而非bean中的属性,注意这里不会自动生成
class_id属性，所以在bean.StudentBean类中要有一个外键的映射属性-->
<one-to-many class="bean.StudentBean"/> <!--指定了“多”端对应的类-->
</set>
</class>
</hibernate-mapping>
- StudentBean.hbml.xml
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!--
Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
<class name="bean.StudentBean" table="t_student" catalog="test">
<id name="stuid" type="java.lang.Integer">
<column name="stuid" />
<generator class="assigned"></generator>
</id>
<property name="stuname" type="java.lang.String">
<column name="stuname" />
</property>
<property name="classId" type="java.lang.Integer">
<column name="class_id" />
</property>
</class>
</hibernate-mapping>
- 测试类
package action; import java.util.Set; import org.hibernate.Session;
import org.hibernate.Transaction; import bean.ClassBean;
import bean.StudentBean;
import util.HibernateUtil; /**
* 本类测试一对多的操作
* @author 半颗柠檬、
*
*/
public class Test_ManytoOne {
public static void main(String[] args) {
// Test_ManytoOne.save(); // Test_ManytoOne.select(); Test_ManytoOne.delete();
} public static void save(){
Session session = null;
Transaction tran = null;
try {
session = HibernateUtil.getSessionFactory().getCurrentSession();
tran=session.beginTransaction(); ClassBean class1=new ClassBean();
class1.setClassid(1);
class1.setClassname("精英班"); StudentBean stu1=new StudentBean();
stu1.setClassId(class1.getClassid());
stu1.setStuid(1);
stu1.setStuname("学生1"); StudentBean stu2=new StudentBean();
stu2.setStuid(2);
stu2.setStuname("学生2");
stu2.setClassId(class1.getClassid()); session.save(class1);
session.save(stu1);
session.save(stu2); tran.commit();
} catch (Exception e) {
e.printStackTrace();
tran.rollback();
}
} /**
* 测试“一”方能够读取“多”方的信息
*/
private static void select() {
Session session = null;
Transaction tran = null;
try {
session = HibernateUtil.getSessionFactory().getCurrentSession();
tran=session.beginTransaction(); /**
* 由“一”方得知“多”方信息
*/ ClassBean cla=(ClassBean)session.get(ClassBean.class, new Integer(1)); Set<StudentBean> stuSet=cla.getStuSet(); for(StudentBean stu:stuSet){ System.out.println(stu.getStuname());
System.out.println(stu.getClassId());
System.out.println(stu.getStuid());
} tran.commit();
} catch (Exception e) {
e.printStackTrace();
tran.rollback();
}
} /**
* 删除One一方时，默认不会级联删除Many的一方。
*
* 如果要级联删除：，一般使用代码手动级联更新
*
* A：使用代码来控制级联删除。也是推荐使用的方式，手动进行级联删除，
*
* B：配置级联关系，让Hibernate自动执行。
*
* 在关联关系中配置cascade属性。
*
* @OneToMany(cascade = { CascadeType.REMOVE, CascadeType.MERGE })
*
*/
private static void delete() {
Session session = null;
Transaction tx = null;
try {
session = HibernateUtil.getSession();
tx = session.beginTransaction(); /**
* B 在关联关系中配置cascade属性之后
*/
ClassBean class1 = (ClassBean) session.get(ClassBean.class,
new Integer(1));
session.delete(class1); tx.commit();
} catch (Exception e) {
e.printStackTrace();
tx.rollback();
} finally {
HibernateUtil.closeSession();
}
} }
案例二：使用注解测试单向一对多操作
- 一个班级有多个学生，班级可以查看所有学生的信息，但是学生不能查看班级的信息。
- ClassBean.java
package bean; import java.io.Serializable;
import java.util.HashSet;
import java.util.Set; import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;
import javax.persistence.Table; @Entity
@Table(name = "t_class")
public class ClassBean implements Serializable {
@Id
private Integer classId; private String className; @OneToMany
@JoinColumn(name = "class_id") //不会在本类中自动创建名为classes_id的属性因为只有“多”方有外键，Hibernate会自动把本类中的所有属性都映射为数据库中的字段，所以该属性要
//和表中的外键名一致，且Hibernate默认与StudentBean的主键相关联
private Set<StudentBean> stuSet=new HashSet<StudentBean>(); public ClassBean() { } public ClassBean(Integer classId, String className) {
super();
this.classId = classId;
this.className = className;
} public Integer getClassId() {
return classId;
} public void setClassId(Integer classId) {
this.classId = classId;
} public String getClassName() {
return className;
} public void setClassName(String className) {
this.className = className;
} public Set<StudentBean> getStuSet() {
return stuSet;
} public void setStuSet(Set<StudentBean> stuSet) {
this.stuSet = stuSet;
}
}
- StudentBean.java
package bean; import java.io.Serializable; import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table; @Entity
@Table(name = "t_student")
public class StudentBean implements Serializable { @Id
@Column(name = "stuid")
private Integer studentId; @Column(name = "stuname")
private String studentName; @Column(name="class_id")
private Integer classid; public StudentBean() { } public StudentBean(Integer studentId, String studentName) {
super();
this.studentId = studentId;
this.studentName = studentName;
} public Integer getStudentId() {
return studentId;
} public void setStudentId(Integer studentId) {
this.studentId = studentId;
} public String getStudentName() {
return studentName;
} public void setStudentName(String studentName) {
this.studentName = studentName;
} public Integer getClassid() {
return classid;
} public void setClassid(Integer classid) {
this.classid = classid;
} }
- 设置总配置文件的映射关系
<mapping class="bean.ClassBean" />
<mapping class="bean.StudentBean" />
- 测试一对多的操作
package action; import java.util.List;
import java.util.Set; import javax.persistence.CascadeType;
import javax.persistence.OneToMany; import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction; import bean.ClassBean;
import bean.StudentBean;
import util.HibernateUtil; /**
* 本类测试一对多的操作
*
* @author 半颗柠檬、
*
*/
public class Test_ManytoOne {
public static void main(String[] args) {
// Test_ManytoOne.save(); // Test_ManytoOne.select(); Test_ManytoOne.delete();
} public static void save() {
Session session = null;
Transaction tran = null;
try {
session = HibernateUtil.getSessionFactory().getCurrentSession();
tran = session.beginTransaction(); ClassBean class1 = new ClassBean();
class1.setClassid(1);
class1.setClassname("精英班"); StudentBean stu1 = new StudentBean();
stu1.setClassid(class1.getClassid());
stu1.setStuid(1);
stu1.setStuname("学生1"); StudentBean stu2 = new StudentBean();
stu2.setStuid(2);
stu2.setStuname("学生2");
stu2.setClassid(class1.getClassid()); session.save(class1);
session.save(stu1);
session.save(stu2); tran.commit();
} catch (Exception e) {
e.printStackTrace();
tran.rollback();
}
} /**
* 测试“一”方能够读取“多”方的信息
*/
private static void select() {
Session session = null;
Transaction tran = null;
try {
session = HibernateUtil.getSessionFactory().getCurrentSession();
tran = session.beginTransaction(); /**
* 由“一”方得知“多”方信息
*/ ClassBean cla = (ClassBean) session.get(ClassBean.class,
new Integer(1));
Set<StudentBean> stuSet = cla.getStuSet(); for (StudentBean stu : stuSet) { System.out.println(stu.getStuname() + "\t" + stu.getStuid()
+ "\t" + stu.getClassid()); }
// 过滤后的数据 ,这种方式会把排序注解忽略掉，即排序注解不会生效
System.out.println("过滤后的数据.......");
Query query = session.createFilter(stuSet,
" where stuid in (2,3)");
List<StudentBean> stuList = query.list();
for (StudentBean stu : stuList) { System.out.println(stu.getStuname() + "\t" + stu.getStuid()
+ "\t" + stu.getClassid()); } /**
* 使用HQL语句。
*/ System.out.println("使用HQL语句");
String hql = " select u from StudentBean u where stuid in(2,3) order by stuid desc ";
query = session.createQuery(hql);
stuList = query.list(); for (StudentBean stu : stuList) { System.out.println(stu.getStuname() + "\t" + stu.getStuid()
+ "\t" + stu.getClassid()); } tran.commit();
} catch (Exception e) {
e.printStackTrace();
tran.rollback();
}
} /**
* 删除one一方的时候，一般不删除多方，Hibernate会自动把多方的外键置空
*/
private static void delete() {
Session session = null;
Transaction tx = null;
try {
session = HibernateUtil.getSession();
tx = session.beginTransaction(); /**
* B 在关联关系中配置cascade属性之后
*/
ClassBean class1 = (ClassBean) session.get(ClassBean.class,
new Integer(1));
session.delete(class1); tx.commit();
} catch (Exception e) {
e.printStackTrace();
tx.rollback();
} finally {
HibernateUtil.closeSession();
}
} }
- 对于项目中大量使用@Entity注册在类头上,将一个类声明为一个实体bean(即一个持久化POJO类) , @Table注册在类头上,注解声明了该实体bean映射指定的表,来体现实体与表的这种映射关系。
对于属性字段和表的字段关系对应的注解属性的位置，一般我们采用以下两种方式:
第一种：
是把注解@Column(name ="xx")放在field上，一种是把注解放在get方法上一般放在field上看起来比较集中、清晰；
第二种：
是把注解@Column(name= "xx")放在get方法上，这种方式看起来比较散漫、不很清楚；
但是第一种方式这样做实际上破坏了Java面向对象的封装性，原因是一般我们写javaBean，成员变量通常定义为private，目的就是不让别人来直接访问的私有属性，而我们把注解放在私有成员的变量上，就是默认hibernate可以直接访问我们的私有的成员变量，所以我们定义属性为private，就实际没有多大意义，至于hibernate为什么能访问，hibernate采用java的反射机制完全可以访问私有成员变量！所以应该放在get方法上，第二种方式这个时候就显得更加合理。
- 注意 ：注意的一点,在一个实体类中，要么将映射注解全部放在成员变量上，要么全部放在成员方法上，不能各放一部分