Hibernate 多对多例-优快云博客

本文介绍了一种在Hibernate框架中实现多对多关联关系的方法，通过定义Group和Role两个实体类及其之间的关联表tgroup_role，展示了如何使用Hibernate进行多对多关系映射。

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create table tgroup ( group_id int not null auto_increment, name varchar(16) not null default '', primary key (group_id) ) type=innodb; create table trole ( role_id int not null auto_increment, name varchar(16) not null default '', primary key (role_id) ) type=innodb; create table tgroup_role ( group_id int not null, role_id int not null, primary key(group_id, role_id), index (group_id), foreign key (group_id) references tgroup(group_id), index (role_id), foreign key (role_id) references trole(role_id) ) type=innodb;
package ivan.hibernate.many2many; public class Group { private int id; private String name; private Set roles = new HashSet(); ... }

Group.hbm.xml

<hibernate-mapping> <class name="ivan.hibernate.many2many.Group" table="tgroup"> <id name="id" column="group_id" unsaved-value="0"> <generator class="increment"/> </id> <property name="name" type="string"/> <set name="roles" table="tgroup_role" cascade="save-update"> <key column="group_id"/> <many-to-many class="ivan.hibernate.many2many.Role" column="role_id"/> </set> </class> </hibernate-mapping>

package ivan.hibernate.many2many; public class Role { private int id; private String name; private Set groups = new HashSet(); ... }

Role.hbm.xml：

<hibernate-mapping> <class name="ivan.hibernate.many2many.Role" table="trole"> <id name="id" column="role_id" unsaved-value="0"> <generator class="increment"/> </id> <property name="name" type="string"/> <set name="groups" table="tgroup_role" inverse="true" cascade="save-update"> <key column="role_id"/> <many-to-many class="ivan.hibernate.many2many.Group" column="group_id"/> </set> </class> </hibernate-mapping>