（十五）Hibernate中的多表操作（5）：双向多对多

• Hibernate的双向关联。
  
      对象之间可以相互读取。
      
      双向只针对读取的操作。对于增、删除、改的操作没有任何影响。

---

 案例 ： 实现双向多对多

• MenuBean.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.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name = "menu")
public class MenuBean implements Serializable {
    @Id
    private Integer menuid;
    private String menuname;

    @ManyToMany
    @JoinTable(name = "role_menu",  //指定数据库中的中间表
    joinColumns = @JoinColumn(name = "menu_id"),  //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menu_id，使它指向当前表的主键这里是menuid 
    inverseJoinColumns = @JoinColumn(name = "roleid")  //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roleid，使它指向对方表的主键。
 
    )
    private Set<RoleBean> roleSet = new HashSet<RoleBean>();

    public MenuBean(Integer menuid, String menuname) {
        super();
        this.menuid = menuid;
        this.menuname = menuname;
    }

    public MenuBean() {
        super();
        // TODO Auto-generated constructor stub
    }

    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;
    }

    public Set<RoleBean> getRoleSet() {
        return roleSet;
    }

    public void setRoleSet(Set<RoleBean> roleSet) {
        this.roleSet = roleSet;
    }

}

• 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.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", 
    joinColumns = @JoinColumn(name = "roleid"), 
    inverseJoinColumns = @JoinColumn(name = "menu_id"))
    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() {
        super();
        // TODO Auto-generated constructor stub
    }

    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;
    }

}

• 添加到总配置文件即可实现。