hibernate多对多关系映射 Mr

多对多关系操作对象

 

FORUM自定义论坛表

FORUM_TOPIC论坛帖子表

FORUM_TOPIC_RELATION论坛主题关系表

其中一个自定义的论坛对应多个论坛帖子

一个帖子也可以存在于多个主题的论坛中

这里以相对比较方便的jpa注解方式 anotation

Hibernate中对多多关系所产生的尸体主要有两种方式，一种是产生两个实体，一种是产生三个实体将关系表也产生实体

产生两个实体配置方式和查询：

package com.tkbs.domain.forum;

import java.util.Date;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

/**
 * Forum entity.<br>
 * 社区/论坛
 * 
 * @author zxg
 */
@Entity
@Table(name ="FORUM")
publicclass Forum implements java.io.Serializable {

    privatestaticfinallong serialVersionUID =-2129436454756881543L;
    private Long id;      //主键
private String title; //自定义论坛名称
private Date cdate;   //自定义论坛创建时间
private String description; //论坛描述
private Set<ForumTopic> forumTopic=new HashSet<ForumTopic>(); //帖子的集合
    
    

    @Id
    @GeneratedValue
    @Column(name ="ID")
    public Long getId() {
        return id;
    }

    publicvoid setId(Long id) {
        this.id = id;
    }


    @Column(name ="TITLE")
    public String getTitle() {
        return title;
    }

    publicvoid setTitle(String title) {
        this.title = title;
    }

    @Temporal(TemporalType.TIMESTAMP)
    @Column(name ="cdate")
    public Date getCdate() {
        return cdate;
    }

    publicvoid setCdate(Date cdate) {
        this.cdate = cdate;
    }

    @Column(name ="DESCRIPTION")
    public String getDescription() {
        return description;
    }

    publicvoid setDescription(String description) {
        this.description = description;
    }

    
    /**
     * inverseJoinColumns: inverse反转的意思，在JPA中可以理解为被维护端
     * inverseJoinColumns中的@JoinColumn: 被维护端外键的定义 forum_id:指中间表那个外键字段与学生表关联
     * joinColumns: 关系维护端的定义
     */
    
    @ManyToMany(cascade = CascadeType.REFRESH, targetEntity = ForumTopic.class, fetch = FetchType.LAZY)
    @JoinTable(name ="forum_topic_relation", inverseJoinColumns = @JoinColumn(name ="topic_id"), joinColumns = @JoinColumn(name ="forum_id"))
    
    
    public Set<ForumTopic> getForumTopic() {
        return forumTopic;
    }

    publicvoid setForumTopic(Set<ForumTopic> forumTopic) {
        this.forumTopic = forumTopic;
    }
    
}

FORUM-_TOPIC对应entity、

package com.tkbs.domain.forum;

import java.util.Date;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.Lob;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;



/**
 * ForumTopic entity.<br>
 * 社区帖子
 * 
 * @author zxg
 */
@Entity
@Table(name ="FORUM_TOPIC")
publicclass ForumTopic implements java.io.Serializable {

    privatestaticfinallong serialVersionUID =6327101690347988478L;
    private Long id;        //主键
private String title;   //帖子标题
private Date cdate;     //帖子创建时间
private String content; //帖子内容
private Long accessTimes;//帖子访问次数
private Long commentTimes;//帖子评论时间
private Integer setTop;   //置顶
private Integer setPerfect;//加精
private Set<Forum> forum =new HashSet<Forum>(); //自定义论坛板块集合

    @Id
    @GeneratedValue
    @Column(name ="ID")
    public Long getId() {
        return id;
    }

    publicvoid setId(Long id) {
        this.id = id;
    }

    
    @Column(name ="TITLE")
    public String getTitle() {
        return title;
    }

    publicvoid setTitle(String title) {
        this.title = title;
    }

    @Temporal(TemporalType.TIMESTAMP)
    @Column(name ="cdate")
    public Date getCdate() {
        return cdate;
    }

    publicvoid setCdate(Date cdate) {
        this.cdate = cdate;
    }

    
    @Lob
    @Column(name ="CONTENT")
    public String getContent() {
        return content;
    }

    publicvoid setContent(String content) {
        this.content = content;
    }
    
    @Column(name ="ACCESS_TIMES")
    public Long getAccessTimes() {
        return accessTimes;
    }

    publicvoid setAccessTimes(Long accessTimes) {
        this.accessTimes = accessTimes;
    }

    @Column(name ="COMMENT_TIMES")
    public Long getCommentTimes() {
        return commentTimes;
    }

    publicvoid setCommentTimes(Long commentTimes) {
        this.commentTimes = commentTimes;
    }

    

    @Column(name ="SET_TOP")
    public Integer getSetTop() {
        return setTop;
    }

    publicvoid setSetTop(Integer setTop) {
        this.setTop = setTop;
    }

    @Column(name ="SET_PERFECT")
    public Integer getSetPerfect() {
        return setPerfect;
    }

    publicvoid setSetPerfect(Integer setPerfect) {
        this.setPerfect = setPerfect;
    }

    
    /**
     * inverseJoinColumns: inverse反转的意思，在JPA中可以理解为被维护端
     * inverseJoinColumns中的@JoinColumn: 被维护端外键的定义 topic_id:指中间表那个外键字段与帖子表关联
     * joinColumns: 关系维护端的定义
     */
    @ManyToMany(cascade = CascadeType.PERSIST, targetEntity = ForumTopic.class, fetch = FetchType.LAZY)
    @JoinTable(name ="forum_topic_relation", inverseJoinColumns = @JoinColumn(name ="forum_id"), joinColumns = @JoinColumn(name ="topic_id"))
    
    public Set<Forum> getForum() {
        return forum;
    }

    publicvoid setForum(Set<Forum> forum) {
        this.forum = forum;
    }

}

多对多关系表的操作：