確保JPQL或SQL的唯一性（獨特記錄）？或兩者？

Question

如何防止TopLink複製現有數據？用Java代碼做這件事還是個好主意，還是應該將它嵌入數據庫並讓插入失敗？

在這種情況下，我想確保newsgroups.newsgroup是唯一的，並且articles.header_id_string也是唯一的。

也許最好的方法是簡單地在Java JPQL中運行唯一性查詢？

模式：

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> 

新聞組實體：

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 + " ]"; 
    } 

} 

與物品實體：

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 + " ]"; 
    } 
} 

Answer 1

應該是建成數據庫，並讓插入失敗？

當然，把它放到數據庫中。

這是您的「最後一道防線」，幾乎沒有辦法繞過它。我只有它你的Java代碼，你不會受到錯誤的SQL腳本或編程錯誤的保護。

您仍然可以檢查您的代碼，例如，向用戶顯示更好的錯誤消息。