Hibernate:对象关联关系映射
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2022-06-13 22:05:29
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Hibernate实现对象与关系之间的映射,通过对对象的操作实现关系的存储,在数据库中实体之间可能会有一定的联系,例如在通用权限管理系统中会有用户和角色实体,用户和角色之间具有一定的联系,即用户拥有一定的角色,所以数据库中会出现3个表,用户表,角色表,用户角色表。其中用户角色表中存在一定的约束,主键分别是用户表和角色表的外键,用户角色表中的用户id必须来自用户表。在使用Hibernate实现时可以使用三个对象来分别对应三张表,但这样对象之间就缺乏了这种关联信息,而且不能保证这种约束关系,为了实现这种约束,Hibernate使用了对象关联关系映射。
1)首先配置hibernate配置文件,包括两个对象关系映射文件,分别对应两个类,用户和角色:
<hibernate-configuration> <session-factory > <!-- local connection properties --> <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/example</property> <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property> <property name="hibernate.connection.username">mzuser</property> <property name="hibernate.connection.password">123456</property> <!-- property name="hibernate.connection.pool_size"></property --> <!-- dialect for MySQL --> <property name="dialect">org.hibernate.dialect.MySQLDialect</property> <property name="hibernate.show_sql">true</property> <property name="hibernate.transaction.factory_class">org.hibernate.transaction.JDBCTransactionFactory</property> <mapping resource="com/mz/bean/UserBean.hbm.xml"/> <mapping resource="com/mz/bean/RoleBean.hbm.xml"/> //对象关系映射配置文件 </session-factory> </hibernate-configuration>
2)数据库中有三张表,用户、角色和用户角色表:
mysql> desc CmsUser; +----------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------+-------------+------+-----+---------+----------------+ | userid | int(8) | NO | PRI | NULL | auto_increment | | username | varchar(20) | NO | UNI | NULL | | | password | varchar(20) | YES | | NULL | | | area | varchar(10) | YES | | NULL | | | deptrole | varchar(10) | YES | | NULL | | +----------+-------------+------+-----+---------+----------------+ 5 rows in set (0.00 sec) mysql> desc CmsRole; +----------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------+-------------+------+-----+---------+----------------+ | roleid | int(8) | NO | PRI | NULL | auto_increment | | rolename | varchar(20) | NO | UNI | NULL | | +----------+-------------+------+-----+---------+----------------+
mysql> desc CmsUserRole; +--------+--------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------+--------+------+-----+---------+-------+ | userid | int(8) | NO | PRI | 0 | | | roleid | int(8) | NO | PRI | 0 | | +--------+--------+------+-----+---------+-------+ 2 rows in set (0.00 sec)
3)用户和角色两个类的定义,用户和角色属于多对多的关系,即一个用户可以具有多个角色,一个角色也可以被多个用户拥有,为了表示用户和角色的这种关联,在用户类中定义一个集合,表示用户拥有多个角色,对应到关系中的用户角色表:
package com.mz.bean; import java.util.HashSet; import java.util.Set; /** * Created by hadoop on 15-9-9. */ public class UserBean { private int userId; private String userName; private String password; private String area; private String deptRole; private Set<RoleBean> roles = new HashSet<RoleBean>(); public int getUserId() { return userId; } public void setUserId(int userid) { this.userId = userid; } public String getUserName() { return userName; } public void setUserName(String username) { this.userName = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public String getArea() { return area; } public void setArea(String area) { this.area = area; } public String getDeptRole() { return deptRole; } public void setDeptRole(String deptrole) { this.deptRole = deptrole; } public Set<RoleBean> getRoles() { return roles; } public void setRoles(Set<RoleBean> roles) { this.roles = roles; } }
package com.mz.bean; /** * Created by hadoop on 15-9-14. */ public class RoleBean { private int roleId; private String roleName; public int getRoleId() { return roleId; } public void setRoleId(int roleId) { this.roleId = roleId; } public String getRoleName() { return roleName; } public void setRoleName(String roleName) { this.roleName = roleName; } }
4)对象关系映射配置文件
<?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.mz.bean"> <class name="com.mz.bean.UserBean" table="CmsUser"> <id name="userId" type="int"> <column name="userid"></column> <generator class="increment"/> </id> <property name="userName" type="java.lang.String"> <column name="username" length="20"></column> </property> <property name="password" type="java.lang.String"> <column name="password" length="20"></column> </property> <property name="area" type="java.lang.String"> <column name="area" length="10"></column> </property> <property name="deptRole" type="java.lang.String"> <column name="deptrole" length="10"></column> </property> <!--对象关联关系映射--> <set name="roles" table="CmsUserRole"> <key column="userid"></key> <many-to-many column="roleid" class="com.mz.bean.RoleBean" unique="true"/> </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.mz.bean"> <class name="com.mz.bean.RoleBean" table="CmsRole"> <id name="roleId" type="int"> <column name="roleid"></column> <generator class="increment"/> </id> <property name="roleName" type="java.lang.String"> <column name="rolename" length="20"></column> </property> </class> </hibernate-mapping>
5)测试类:创建多个用户对象和角色对象,并在用户对象中加入拥有角色的集合,最后save()用户和角色对象。
@Test public void testMMMap(){ UserBean userBean1 = new UserBean(); UserBean userBean2 = new UserBean(); RoleBean roleBean1 = new RoleBean(); RoleBean roleBean2 = new RoleBean(); RoleBean roleBean3 = new RoleBean(); userBean1.setUserName("admin1"); userBean1.setPassword("123456"); userBean2.setUserName("normal"); userBean2.setPassword("123456"); roleBean1.setRoleName("admin"); roleBean2.setRoleName("commerce"); roleBean3.setRoleName("finance"); userBean1.getRoles().add(roleBean1); userBean1.getRoles().add(roleBean2); userBean2.getRoles().add(roleBean1); userBean2.getRoles().add(roleBean3); Session session = SessionUtil.getSession(); org.hibernate.Transaction ta = session.beginTransaction(); session.save(userBean1); session.save(userBean2); session.save(roleBean1); session.save(roleBean2); session.save(roleBean3); ta.commit(); SessionUtil.closeSession(); }
6) 结果查询:查询数据库发现三张表中都插入了新的数据,其中用户角色表中有用户关系与角色关系的联系。
mysql> select * from CmsUser; +--------+----------+----------+------+----------+ | userid | username | password | area | deptrole | +--------+----------+----------+------+----------+ | 1 | admin1 | 123456 | NULL | NULL | | 2 | normal | 123456 | NULL | NULL | +--------+----------+----------+------+----------+ 2 rows in set (0.00 sec) mysql> select * from CmsRole; +--------+----------+ | roleid | rolename | +--------+----------+ | 1 | admin | | 2 | commerce | | 3 | finance | +--------+----------+ 3 rows in set (0.00 sec) mysql> select * from CmsUserRole; +--------+--------+ | userid | roleid | +--------+--------+ | 1 | 1 | | 2 | 1 | | 1 | 2 | | 2 | 3 | +--------+--------+ 4 rows in set (0.00 sec)