HiberNate学习-三 映射关系

HiberNate学习-3 映射关系

1 Hibernate的一对多关联映射

核心代码：

<set name="students"><key column="classesId"/><one-to-many alt="HiberNate学习-三 映射关系">
package com.tao.hibernate.one2many;import java.util.Set;public class Classes {private Integer id;private String name;private Set<Students> students;public Classes() {super();}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Set<Students> getStudents() {return students;}public void setStudents(Set<Students> students) {this.students = students;}}
package com.tao.hibernate.one2many;public class Students {private Integer id;private String name;private Classes classes;public Students() {super();}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Classes getClasses() {return classes;}public void setClasses(Classes classes) {this.classes = classes;}}

二：映射文件：


<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.tao.hibernate.one2many"><class name="Classes" table="t_classes"><id name="id" column="id" type="integer"><generator /></id><property name="name" column="name" /><set name="students"><key column="classId"/><one-to-many alt="HiberNate学习-三 映射关系">
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.tao.hibernate.one2many"><class name="Students" table="t_students"><id name="id" column="id" type="integer"><generator /></id><property name="name" column="name" /></class></hibernate-mapping>

三：测试类：



<set name="students" inverse="true" cascade="all">
<key column="classesId" />
<one-to-many />
</set>

?

hihernate一对多关联映射（双向Classes<----->Student）

一对多双向关联映射：
* 在一一端的集合上使用<key>，在对方表中加入一个外键指向一一端
* 在多一端采用<many-to-one>

注意：<key>标签指定的外键字段必须和<many-to-one>指定的外键字段一致，否则引用字段的错误

如果在”一“一端维护一对多关联关系，hibernate会发出多余的udpate语句，所以我们一般在多
的一端来维护关联关系

关于inverse属性：
inverse主要用在一对多和多对多双向关联上，inverse可以被设置到集合标签<set>上，
默认inverse为false，所以我们可以从”一“一端和”多“一端维护关联关系，
如果设置成inverse为true，则我们只能从多一端来维护关联关系

注意：inverse属性，只影响数据的存储，也就是持久化

inverse和cascade
* inverse是关联关系的控制方向
* cascade操作上的连锁反应

?

一：实体类：


package com.tao.hibernate.one2many2;import java.util.Set;public class Classes {private Integer id;private String name;private Set<Students> students;public Classes() {super();}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Set<Students> getStudents() {return students;}public void setStudents(Set<Students> students) {this.students = students;}}

?


package com.tao.hibernate.one2many2;public class Students {private Integer id;private String name;private Classes classes;public Students() {super();}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Classes getClasses() {return classes;}public void setClasses(Classes classes) {this.classes = classes;}}

?

二：映射文件：


<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.tao.hibernate.one2many2" auto-import="false"><class name="Classes" table="t_classes"><id name="id" column="id" type="integer"><generator /></id><property name="name" column="name" /><set name="students" inverse="true" cascade="all"><key column="classesId" /><one-to-many /></set></class></hibernate-mapping>

?


<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.tao.hibernate.one2many2" auto-import="false"><class name="Students" table="t_students"><id name="id" column="id" type="integer"><generator /></id><property name="name" column="name" /><many-to-one name="classes" column="classesId"/></class></hibernate-mapping>

?

三：测试类：

<key column="userid"/>
<many-to-many column="roleid"/>
</set>

?

一：实体类：


package com.tao.hibernate.many2many;public class Role {private Integer id;private String name;public Role() {super();}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}}

?


package com.tao.hibernate.many2many;import java.util.Set;public class User {private Integer id;private String name;private Set<Role> roles;public User() {super();}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Set<Role> getRoles() {return roles;}public void setRoles(Set<Role> roles) {this.roles = roles;}}

?

二：映射文件：


<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.tao.hibernate.many2many"><class name="Role" table="t_role"><id name="id" column="id" type="integer"><generator column="name" /></class></hibernate-mapping>

?


<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.tao.hibernate.many2many"auto-import="false"><class name="User" table="t_user"><id name="id" column="id" type="integer"><generator column="name" /><set name="roles" table="t_user_role" cascade="all"><key column="userId" /><many-to-many column="roleId" /></set></class></hibernate-mapping>

?

三：测试类：


package com.tao.hibernate.many2many; import java.util.HashSet; import java.util.Iterator; import java.util.Set; import org.hibernate.Session; import org.hibernate.Transaction; import org.junit.Test; import com.tao.hibernate.HibernateUtils; public class TestMain { Session session = HibernateUtils.getFactory().openSession(); @Test public void testSave() { User u1 = new User(); u1.setName("u1"); User u2 = new User(); u2.setName("u2"); User u3 = new User(); u3.setName("u3"); Role r1 = new Role(); r1.setName("admin"); Role r2 = new Role(); r2.setName("guest"); Set<Role> roles1 = new HashSet<Role>(); roles1.add(r1); Set<Role> roles2 = new HashSet<Role>(); roles2.add(r2); Set<Role> roles3 = new HashSet<Role>(); roles3.add(r1); roles3.add(r2); u1.setRoles(roles1); u2.setRoles(roles2); u3.setRoles(roles3); Transaction ts = session.beginTransaction(); ts.begin(); session.save(u1); session.save(u2); session.save(u3); ts.commit(); } @Test public void testLoad() { Session session = HibernateUtils.getFactory().openSession(); User u1 = (User) session.load(User.class, 1); System.out.println(u1.getName()); for (Iterator<Role> iter = u1.getRoles().iterator(); iter.hasNext();) { System.out.println(iter.next().getName()); } } }