（十三）Hibernate中的多表操作（3）：单向多对多
- 多对多的处理方式是，有一张中间表，中间表保存两个多方之间的关系。首先来看实际应用场景：在之前开发的系统中，应用了基于角色的控制访问，也就是RBAC模型，一个用户可能存在多种角色，一种角色也可能有多个用户，所以用户和角色之间是一个多对多的关系。
案例一： 使用注解方式实现多对多关系
- RoleBean.java
package bean; import java.io.Serializable; import java.util.HashSet; import java.util.Set; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.JoinColumns; import javax.persistence.JoinTable; import javax.persistence.ManyToMany; import javax.persistence.Table; @Entity @Table(name = "role") public class RoleBean implements Serializable { @Id private Integer role_id; private String role_name; private String role_remark; @ManyToMany @JoinTable(name = "role_menu", // //name=”role_menu”中间表的名称是“role_menu” joinColumns = { @JoinColumn(name = "roleid") }, //设置当前实体在中间表中的映射，也就是说在中间表中有一个字段叫roleid，使它指向当前表的主键这里是role_id inverseJoinColumns = { @JoinColumn(name = "menu_id") }) //设置对方实体在中间中的映射，也就是说在中间表中有一个字段menu_id，使它指向对方表(menu表)的主键。 private Set<MenuBean> menuSet = new HashSet<MenuBean>(); public RoleBean(Integer role_id, String role_name, String role_remark) { super(); this.role_id = role_id; this.role_name = role_name; this.role_remark = role_remark; } public RoleBean() { } public Integer getRole_id() { return role_id; } public void setRole_id(Integer role_id) { this.role_id = role_id; } public String getRole_name() { return role_name; } public void setRole_name(String role_name) { this.role_name = role_name; } public String getRole_remark() { return role_remark; } public void setRole_remark(String role_remark) { this.role_remark = role_remark; } public Set<MenuBean> getMenuSet() { return menuSet; } public void setMenuSet(Set<MenuBean> menuSet) { this.menuSet = menuSet; } }
- MenuBean.java
package bean; import java.io.Serializable; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.Table; @Entity @Table(name = "menu") public class MenuBean implements Serializable { @Id private Integer menuid; private String menuname; public MenuBean() { } public MenuBean(Integer menuid, String menuname) { super(); this.menuid = menuid; this.menuname = menuname; } public Integer getMenuid() { return menuid; } public void setMenuid(Integer menuid) { this.menuid = menuid; } public String getMenuname() { return menuname; } public void setMenuname(String menuname) { this.menuname = menuname; } }
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把两个含有注解的bean文件添加到总配置文件里即可实现。
案例二：使用xml配置文件实现单向多对多
- 创建实体类 Role.java
package bean; import java.util.HashSet; import java.util.Set; /** * Role entity. @author MyEclipse Persistence Tools */ public class Role implements java.io.Serializable { // Fields private Integer roleId; private String roleName; private String roleRemark; private Set<MenuBean> menuSet=new HashSet<MenuBean>(); // Constructors /** default constructor */ public Role() { } /** minimal constructor */ public Role(Integer roleId) { this.roleId = roleId; } /** full constructor */ public Role(Integer roleId, String roleName, String roleRemark) { this.roleId = roleId; this.roleName = roleName; this.roleRemark = roleRemark; } // Property accessors public Integer getRoleId() { return this.roleId; } public void setRoleId(Integer roleId) { this.roleId = roleId; } public String getRoleName() { return this.roleName; } public void setRoleName(String roleName) { this.roleName = roleName; } public String getRoleRemark() { return this.roleRemark; } public void setRoleRemark(String roleRemark) { this.roleRemark = roleRemark; } public Set<MenuBean> getMenuSet() { return menuSet; } public void setMenuSet(Set<MenuBean> menuSet) { this.menuSet = menuSet; } }
- 创建实体类 MenuBean.java
package bean; /** * MenuBean entity. @author MyEclipse Persistence Tools */ public class MenuBean implements java.io.Serializable { // Fields private Integer menuid; private String menuname; /** default constructor */ public MenuBean() { } /** minimal constructor */ public MenuBean(Integer menuid) { this.menuid = menuid; } /** full constructor */ public MenuBean(Integer menuid, String menuname) { this.menuid = menuid; this.menuname = menuname; } // Property accessors public Integer getMenuid() { return this.menuid; } public void setMenuid(Integer menuid) { this.menuid = menuid; } public String getMenuname() { return this.menuname; } public void setMenuname(String menuname) { this.menuname = menuname; } }
- 把创建实体类的映射文件 Role.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.Role" table="role" catalog="test"> <id name="roleId" type="java.lang.Integer"> <column name="role_id" /> <generator class="assigned"></generator> </id> <property name="roleName" type="java.lang.String"> <column name="role_name" /> </property> <property name="roleRemark" type="java.lang.String"> <column name="role_remark" /> </property> <!-- 单向多对多 --> <set name="menuSet" table="role_menu"> <key column="roleid"></key> <!-- 表示当前类映射到关系表中的列 --> <many-to-many column="menu_id" class="bean.MenuBean" ></many-to-many> <!-- 所对应的另一方在关系表中的列 --> </set> </class> </hibernate-mapping>
- MenuBean.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.MenuBean" table="menu" catalog="test"> <id name="menuid" type="java.lang.Integer"> <column name="menuid" /> <generator class="assigned"></generator> </id> <property name="menuname" type="java.lang.String"> <column name="menuname" /> </property> </class> </hibernate-mapping>
- 把两个映射文件添加到总配置文件里即可实现。
