如何防止TopLink复制现有数据？使用Java代码执行此操作甚至是一个好主意，还是应该将其内置到数据库中并让插入失败？
在这种情况下，我想确保newsgroups.newsgroup是唯一的，articles.header_id_string也是唯一的。
最好的方法可能是简单地在Java JPQL中运行唯一性查询吗？
架构：
mysql>
mysql> show tables;
+---------------------+
| Tables_in_nntp |
+---------------------+
| articles |
| newsgroups |
| newsgroups_articles |
+---------------------+
3 rows in set (0.01 sec)
mysql> describe newsgroups;
+-----------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| newsgroup | text | NO | | NULL | |
+-----------+---------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
mysql> describe articles;
+------------------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| subject | text | NO | | NULL | |
| content | text | NO | | NULL | |
| number | int(11) | NO | | NULL | |
| sent | date | NO | | NULL | |
| header_id_string | text | NO | | NULL | |
+------------------+---------+------+-----+---------+----------------+
6 rows in set (0.00 sec)
mysql> describe newsgroups_articles;
+--------------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| article_id | int(11) | NO | | NULL | |
| newsgroup_id | int(11) | NO | MUL | NULL | |
+--------------+---------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
mysql>
新闻组实体：
package net.bounceme.dur.usenet.model;
import java.io.Serializable;
import javax.mail.Folder;
import javax.persistence.*;
import javax.xml.bind.annotation.XmlRootElement;
@Entity
@Table(name = "newsgroups", catalog = "nntp", schema = "")
@XmlRootElement
@NamedQueries({
@NamedQuery(name = "Newsgroups.findAll", query = "SELECT n FROM Newsgroup n"),
@NamedQuery(name = "Newsgroups.findById", query = "SELECT n FROM Newsgroup n WHERE n.id = :id")})
public class Newsgroup implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "id", nullable = false)
private Integer id;
@Basic(optional = false)
@Lob
@Column(name = "newsgroup", nullable = false, length = 65535)
private String newsgroup;
public Newsgroup() {
}
public Newsgroup(Folder f){
newsgroup = f.getFullName();
}
public Newsgroup(Integer id) {
this.id = id;
}
public Newsgroup(Integer id, String newsgroup) {
this.id = id;
this.newsgroup = newsgroup;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getNewsgroup() {
return newsgroup;
}
public void setNewsgroup(String newsgroup) {
this.newsgroup = newsgroup;
}
@Override
public int hashCode() {
int hash = 0;
hash += (id != null ? id.hashCode() : 0);
return hash;
}
@Override
public boolean equals(Object object) {
// TODO: Warning - this method won't work in the case the id fields are not set
if (!(object instanceof Newsgroup)) {
return false;
}
Newsgroup other = (Newsgroup) object;
if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
return false;
}
return true;
}
@Override
public String toString() {
return "net.bounceme.dur.usenet.model.Newsgroups[ id=" + id + " ]";
}
}
文章实体：
package net.bounceme.dur.usenet.model;
import java.io.Serializable;
import java.util.Collection;
import java.util.Date;
import javax.persistence.*;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlTransient;
import net.bounceme.dur.usenet.controller.MessageBean;
@Entity
@Table(name = "articles", catalog = "nntp", schema = "")
@XmlRootElement
@NamedQueries({
@NamedQuery(name = "Articles.findAll", query = "SELECT a FROM Article a"),
@NamedQuery(name = "Articles.findById", query = "SELECT a FROM Article a WHERE a.id = :id"),
@NamedQuery(name = "Articles.findByNumber", query = "SELECT a FROM Article a WHERE a.number = :number"),
@NamedQuery(name = "Articles.findBySent", query = "SELECT a FROM Article a WHERE a.sent = :sent")})
public class Article implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "id", nullable = false)
private Integer id;
@Basic(optional = false)
@Lob
@Column(name = "subject", nullable = false, length = 65535)
private String subject;
@Basic(optional = false)
@Lob
@Column(name = "content", nullable = false, length = 65535)
private String content;
@Basic(optional = false)
@Column(name = "number", nullable = false)
private int number;
@Basic(optional = false)
@Column(name = "sent", nullable = false)
@Temporal(TemporalType.DATE)
private Date sent;
@Basic(optional = false)
@Lob
@Column(name = "header_id_string", nullable = false, length = 65535)
private String headerIdString;
@OneToMany(cascade = CascadeType.ALL, mappedBy = "newsgroupId")
private Collection<NewsgroupsArticles> newsgroupsArticlesCollection;
public Article() {
}
public Article(MessageBean messageBean) {
subject = messageBean.getSubject();
content = messageBean.getContent();
sent = messageBean.getSent();
number = messageBean.getNumber();
headerIdString = "dummy";
}
public Article(Integer id) {
this.id = id;
}
public Article(Integer id, String subject, String content, int number, Date sent, String headerIdString) {
this.id = id;
this.subject = subject;
this.content = content;
this.number = number;
this.sent = sent;
this.headerIdString = headerIdString;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getSubject() {
return subject;
}
public void setSubject(String subject) {
this.subject = subject;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public int getNumber() {
return number;
}
public void setNumber(int number) {
this.number = number;
}
public Date getSent() {
return sent;
}
public void setSent(Date sent) {
this.sent = sent;
}
public String getHeaderIdString() {
return headerIdString;
}
public void setHeaderIdString(String headerIdString) {
this.headerIdString = headerIdString;
}
@XmlTransient
public Collection<NewsgroupsArticles> getNewsgroupsArticlesCollection() {
return newsgroupsArticlesCollection;
}
public void setNewsgroupsArticlesCollection(Collection<NewsgroupsArticles> newsgroupsArticlesCollection) {
this.newsgroupsArticlesCollection = newsgroupsArticlesCollection;
}
@Override
public int hashCode() {
int hash = 0;
hash += (id != null ? id.hashCode() : 0);
return hash;
}
@Override
public boolean equals(Object object) {
// TODO: Warning - this method won't work in the case the id fields are not set
if (!(object instanceof Article)) {
return false;
}
Article other = (Article) object;
if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
return false;
}
return true;
}
@Override
public String toString() {
return "net.bounceme.dur.usenet.model.Articles[ id=" + id + " ]";
}
}
答案 0 :(得分：1)
是否应将内置到数据库中并让插入失败？
当然，把它放到数据库中。
这是你的“最后一道防线”，而且几乎没有办法绕过它。我只有你的Java代码，你没有防止错误的SQL脚本或编程错误。
您仍然可以检查您的代码，例如向用户显示更好的错误消息。