hibernate使用annotation来处理onetomany

云自无心水自闲 — Mon, 10 Aug 2009 05:24:00 GMT

1. 数据库的表结构
CREATE TABLE `software` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(45) NOT NULL,
PRIMARY KEY (`id`)
);

CREATE TABLE `version` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`publish_time` datetime NOT NULL,
`software_id` int(10) unsigned NOT NULL,
PRIMARY KEY (`id`)
);

2. java的class

---------------------------------------
Software.java

import java.util.LinkedHashSet;
import java.util.Set;

import javax.persistence.Entity;

@Entity
public class Software {

    private Long id;
    private String name;
    private Set versions = new LinkedHashSet();

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    @OneToMany(cascade = { CascadeType.ALL }, mappedBy="software")
    @JoinColumn(name = "software_id")
    @Fetch(FetchMode.SUBSELECT)
    @OrderBy("id")
    public Set getVersions() {
        return version;
    }

    public void setVersions(Set Versions) {
        this.versions = versions;
    }
}

-----------------------------------------------------
Version.java

import java.util.Date;
import javax.persistence.Entity;

@Entity
public class Version{
    private Long id;
    private Date publishTime;
    private Software software;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }
    public Date getPublishTime() {
        return publishTime;
    }
    public void setPublishTime(Date publishTime) {
        this.publishTime = publishTime;
    }

    @ManyToOne(cascade = { CascadeType.PERSIST, CascadeType.MERGE })
    @JoinColumn(name = "software_id")
    public Software getSoftware() {
        return software;
    }

    public void setSoftware(Software software) {
        this.software = software;
    }
}

3. 测试代码

Software software = new Software();
software.setName("Windows");

Version version = new Version;
version.setPublishTime(new Date());
version.setSoftware(software);

software.getVersions().add(version);

software.save();

hibernate会自动生成两条insert语句，一条是software的insert语句，一条是version的insert语句。
同样，如果删除software的话，也会生成两条delete语句

云自无心水自闲 2009-08-10 13:24 发表评论

Hibernate启动报错cannot simultaneously fetch multiple bags

云自无心水自闲 — Tue, 30 Dec 2008 05:03:00 GMT

我使用的是annotation方式的hibernate配置。结果在启动Tomcat的时候报错：
Invocation of init method failed; nested exception is org.hibernate.HibernateException: cannot simultaneously fetch multiple bags
解决方法：
去除Annotation中的所有FetchType="EAGAR"

云自无心水自闲 2008-12-30 13:03 发表评论

BlogJava-云自无心水自闲-随笔分类-Hibernate

hibernate使用annotation来处理onetomany

Hibernate启动报错cannot simultaneously fetch multiple bags