Hibernate中ManyToOne,OneToMany,OneToOne的使用例

来源：互联网发布：js原生排序编辑：程序博客网时间：2024/04/29 18:49

有3个表：
News：新闻表
NewsResource：新闻附件表
Resource：资源表

表关系：
1个新闻（News）对应多条新闻附件（NewsResource）
News：ID <---> NewsResource：news_id

1个新闻附件（NewsResource）对应1个资源（Resource）。
NewsResource：resource_id <---> Resource：ID

实体类如下：

News：

@Entity@Table(name="news")public class NewsEntity implements Serializable{    private static final long serialVersionUID = 48L;    @Id    @GeneratedValue    @Column(name="ID")    private Long id;    @OneToMany(cascade=CascadeType.ALL,fetch=FetchType.LAZY,mappedBy="news")    private Set<NewsResourceEntity> newsResource;    //其他内容省略}

NewsResource:
关于NewsResource表，有两种写法：
方法1：
这种写法用于不想和news表做级联更新，只想做级联查询的情况。news_id和resource_id都定义了2次，上面@Column用于自己表的更新，下面的@JoinColumn用于级联查询的时候的Join列。

@Entity@Table(name="newsresource")public class NewsResourceEntity implements Serializable{    private static final long serialVersionUID = 48L;    @Id    @GeneratedValue    @Column(name="ID")    private Long id;    @Column(name = "news_id")    private Long newsId;    @Column(name = "resource_id")    private Long resourceId;    @ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.LAZY)    @JoinColumn(name="news_id", insertable = false,updatable = false)    private NewsEntity news;    @OneToOne(optional = false, cascade = CascadeType.MERGE)    @JoinColumn(name = "resource_id", referencedColumnName = "id", unique = true, insertable = false,updatable = false)    private ResourceEntity resource;    //其他内容省略}

方法2：
这种写法就是典型的级联查询+级联更新。

<pre name="code" class="java">@Entity@Table(name="newsresource")public class NewsResourceEntity implements Serializable{private static final long serialVersionUID = 48L;@Id@GeneratedValue@Column(name="ID")private Long id;@ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.LAZY)@JoinColumn(name="news_id")private NewsEntity news;@OneToOne(optional = false, cascade = CascadeType.MERGE)@JoinColumn(name = "resource_id", referencedColumnName = "id", unique = true)private ResourceEntity resource;        //其他内容省略}

Resource：

@Entity@Table(name="resource")public class ResourceEntity implements Serializable {private static final long serialVersionUID = 48L;@Id@GeneratedValue@Column(name="ID")private Long id;@OneToOne(optional = true, cascade = CascadeType.ALL, fetch=FetchType.LAZY, mappedBy = "resource")private NewsResourceEntity newsResource;        //其他内容省略}

另外，懒加载（LAZY）如果遇到问题，请参照相关文章：
http://blog.csdn.net/sunroyi666/article/details/51890571

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