翻譯SQL加盟JPQL

目前，所有文章中加入了JPQL查詢在getRangeOfArticles方法返回，而只有一個一系列文章應該得到恢復。翻譯SQL加盟JPQL

MySQL控制檯輸出我之後，卻想在JPQL來實現：

mysql> 
mysql> SELECT * FROM articles LEFT OUTER JOIN newsgroups ON articles.NEWSGROUP_ID=newsgroups.ID WHERE newsgroups.NEWSGROUP = "gwene.com.economist" AND articles.ID BETWEEN 450 AND 453; 
+-----+---------------+--------------+------+---------------------+ 
| ID | MESSAGENUMBER | NEWSGROUP_ID | ID | NEWSGROUP   | 
+-----+---------------+--------------+------+---------------------+ 
| 450 |   554 |   5 | 5 | gwene.com.economist | 
| 451 |   555 |   5 | 5 | gwene.com.economist | 
| 452 |   556 |   5 | 5 | gwene.com.economist | 
| 453 |   557 |   5 | 5 | gwene.com.economist | 
+-----+---------------+--------------+------+---------------------+ 
4 rows in set (0.02 sec) 

mysql> 
mysql> show tables; 
+------------------+ 
| Tables_in_usenet | 
+------------------+ 
| articles   | 
| newsgroups  | 
+------------------+ 
2 rows in set (0.01 sec) 

mysql> describe articles; 
+---------------+------------+------+-----+---------+----------------+ 
| Field   | Type  | Null | Key | Default | Extra   | 
+---------------+------------+------+-----+---------+----------------+ 
| ID   | bigint(20) | NO | PRI | NULL | auto_increment | 
| MESSAGENUMBER | int(11) | YES |  | NULL |    | 
| NEWSGROUP_ID | bigint(20) | YES | MUL | NULL |    | 
+---------------+------------+------+-----+---------+----------------+ 
3 rows in set (0.00 sec) 

mysql> describe newsgroups; 
+-----------+--------------+------+-----+---------+----------------+ 
| Field  | Type   | Null | Key | Default | Extra   | 
+-----------+--------------+------+-----+---------+----------------+ 
| ID  | bigint(20) | NO | PRI | NULL | auto_increment | 
| NEWSGROUP | varchar(255) | YES |  | NULL |    | 
+-----------+--------------+------+-----+---------+----------------+ 
2 rows in set (0.00 sec) 

mysql>

我試圖複製該SQL查詢在JPQL在getRangeOfArticles方法：

package net.bounceme.dur.usenet.driver; 

import java.util.List; 
import java.util.logging.Logger; 
import javax.mail.Folder; 
import javax.mail.Message; 
import javax.persistence.*; 
import net.bounceme.dur.usenet.model.Article; 
import net.bounceme.dur.usenet.model.Newsgroup; 

class DatabaseUtils { 

    private static final Logger LOG = Logger.getLogger(DatabaseUtils.class.getName()); 
    private EntityManagerFactory emf = Persistence.createEntityManagerFactory("USENETPU"); 
    private EntityManager em = emf.createEntityManager(); 

    //SELECT MAX(MESSAGENUMBER) FROM articles LEFT OUTER JOIN newsgroups ON articles.NEWSGROUP_ID=newsgroups.ID WHERE newsgroups.NEWSGROUP = "gwene.com.economist"; 
    public int getMaxMessageNumber(Folder folder) { 
     int maxMessageNumber = 0; 
     String newsgroup = folder.getFullName(); 
     String queryString = "select max(article.messageNumber) from Article article left join article.newsgroup newsgroup where newsgroup.newsgroup = '" + newsgroup + "'"; 
     try { 
      maxMessageNumber = (Integer) em.createQuery(queryString).getSingleResult(); 
     } catch (Exception e) { 
      LOG.severe("setting max to zero for " + newsgroup); 
     } 
     LOG.fine(folder.getFullName() + "\t" + maxMessageNumber); 
     return maxMessageNumber; 
    } 

    //SELECT * FROM articles LEFT OUTER JOIN newsgroups ON articles.NEWSGROUP_ID=newsgroups.ID WHERE newsgroups.NEWSGROUP = "gwene.com.economist" AND articles.ID BETWEEN 450 AND 500; 
    public List<Article> getRangeOfArticles(Page page) { 
     String fullNewsgroupName = page.getFolder().getFullName(); 
     int minRange = page.getMin(); 
     int maxRange = page.getMax(); 
     String queryString = "select article from Article article left join article.newsgroup newsgroup where newsgroup.newsgroup = :newsGroupParam"; 
     TypedQuery<Article> query = em.createQuery(queryString, Article.class); 
     query.setParameter("newsGroupParam", fullNewsgroupName); 
     List<Article> results = query.getResultList(); 
     LOG.info(results.toString()); 
     return results; 
    } 

    public void persistArticle(Message message, Folder folder) { 
     em.getTransaction().begin(); 
     String fullNewsgroupName = folder.getFullName(); 
     Newsgroup newsgroup = null; 
     TypedQuery<Newsgroup> query = em.createQuery("SELECT n FROM Newsgroup n WHERE n.newsgroup = :newsGroupParam", Newsgroup.class); 
     query.setParameter("newsGroupParam", fullNewsgroupName); 
     try { 
      newsgroup = query.getSingleResult(); 
      LOG.fine("found " + query.getSingleResult()); 
     } catch (javax.persistence.NoResultException e) { 
      LOG.fine(e + "\ncould not find " + fullNewsgroupName); 
      newsgroup = new Newsgroup(folder); 
      em.persist(newsgroup); 
     } catch (NonUniqueResultException e) { 
      LOG.warning("\nshould never happen\t" + fullNewsgroupName); 
     } /* 
     * finally { if (em.getTransaction().isActive()) { 
     * em.getTransaction().rollback(); } 
     */ 
     Article article = new Article(message, newsgroup); 
     em.persist(article); 
     em.getTransaction().commit(); 
    } 

    public void close() { 
     em.close(); 
     emf.close();//necessary? 
    } 
}

來源

2012-08-06 Thufir

就查詢而言，我相信它是String queryString = "select article from Article article left join article.newsgroup newsgroup where newsgroup.newsgroup = :newsGroupParam and article.messageNumber between 100 and 500";，但我需要在該範圍內添加一些參數。見下面getRangeOfArticles：

package net.bounceme.dur.usenet.driver; 

import java.util.ArrayList; 
import java.util.List; 
import java.util.logging.Level; 
import java.util.logging.Logger; 
import javax.mail.Folder; 
import javax.mail.Message; 
import javax.mail.MessagingException; 
import javax.persistence.*; 
import net.bounceme.dur.usenet.model.Article; 
import net.bounceme.dur.usenet.model.Newsgroup; 
import net.bounceme.dur.usenet.model.Usenet; 

class DatabaseUtils { 

    private static final Logger LOG = Logger.getLogger(DatabaseUtils.class.getName()); 
    private EntityManagerFactory emf = Persistence.createEntityManagerFactory("USENETPU"); 
    private EntityManager em = emf.createEntityManager(); 

    //SELECT MAX(MESSAGENUMBER) FROM articles LEFT OUTER JOIN newsgroups ON articles.NEWSGROUP_ID=newsgroups.ID WHERE newsgroups.NEWSGROUP = "gwene.com.economist"; 
    public int getMaxMessageNumber(Folder folder) { 
     int maxMessageNumber = 0; 
     String newsgroup = folder.getFullName(); 
     String queryString = "select max(article.messageNumber) from Article article left join article.newsgroup newsgroup where newsgroup.newsgroup = '" + newsgroup + "'"; 
     try { 
      maxMessageNumber = (Integer) em.createQuery(queryString).getSingleResult(); 
     } catch (Exception e) { 
      LOG.severe("setting max to zero for " + newsgroup); 
     } 
     LOG.fine(folder.getFullName() + "\t" + maxMessageNumber); 
     return maxMessageNumber; 
    } 

    //SELECT * FROM articles LEFT OUTER JOIN newsgroups ON articles.NEWSGROUP_ID=newsgroups.ID WHERE newsgroups.NEWSGROUP = "gwene.com.economist" AND articles.ID BETWEEN 450 AND 500; 
    public List<Article> getRangeOfArticles(Page page) { 
     String fullNewsgroupName = page.getFolder().getFullName(); 
     int minRange = page.getMin(); 
     int maxRange = page.getMax(); 
     String queryString = "select article from Article article left join article.newsgroup newsgroup where newsgroup.newsgroup = :newsGroupParam and article.messageNumber between 100 and 500"; 
     TypedQuery<Article> query = em.createQuery(queryString, Article.class); 
     query.setParameter("newsGroupParam", fullNewsgroupName); 
     List<Article> articles = query.getResultList(); 
     Usenet usenet = Usenet.INSTANCE; 
     for (Article article : articles) { 
      List<String> string = new ArrayList<>(); 
      string.add(article.getId().toString()); 
      string.add(Long.toString(article.getMessageNumber())); 
      Message message = usenet.getMessage(page.getFolder(), article.getMessageNumber()); 
      try { 
       string.add(message.getSubject()); 
      } catch (MessagingException ex) { 
       Logger.getLogger(DatabaseUtils.class.getName()).log(Level.SEVERE, null, ex); 
      } 
      Newsgroup n = article.getNewsgroup(); 
      string.add(n.getNewsgroup()); 
      LOG.info(string.toString()); 
     } 
     return articles; 
    } 

    public void persistArticle(Message message, Folder folder) { 
     em.getTransaction().begin(); 
     String fullNewsgroupName = folder.getFullName(); 
     Newsgroup newsgroup = null; 
     TypedQuery<Newsgroup> query = em.createQuery("SELECT n FROM Newsgroup n WHERE n.newsgroup = :newsGroupParam", Newsgroup.class); 
     query.setParameter("newsGroupParam", fullNewsgroupName); 
     try { 
      newsgroup = query.getSingleResult(); 
      LOG.fine("found " + query.getSingleResult()); 
     } catch (javax.persistence.NoResultException e) { 
      LOG.fine(e + "\ncould not find " + fullNewsgroupName); 
      newsgroup = new Newsgroup(folder); 
      em.persist(newsgroup); 
     } catch (NonUniqueResultException e) { 
      LOG.warning("\nshould never happen\t" + fullNewsgroupName); 
     } /* 
     * finally { if (em.getTransaction().isActive()) { 
     * em.getTransaction().rollback(); } 
     */ 
     Article article = new Article(message, newsgroup); 
     em.persist(article); 
     em.getTransaction().commit(); 
    } 

    public void close() { 
     em.close(); 
     emf.close();//necessary? 
    } 
}

不過，我似乎得到了一些錯誤：

Aug 06, 2012 12:00:02 AM net.bounceme.dur.usenet.model.Usenet getMessage 
SEVERE: null 
javax.mail.MessageRemovedException: No such article: 273

所以也許有一個與查詢語法或意義的錯誤，或者我有一個邏輯上的錯誤。

來源

2012-08-06 07:04:07 Thufir

似乎你已經回答了你的問題。所以你可以接受它。 – 2012-08-12 18:42:11

如果你想通過自己的Newsgroup的名字來查詢Article個集合，你可以做這樣的事情：

String queryString = "select a from Article a where a.newsgroup.newsgroup = :newsGroupParam"; 
TypedQuery<Article> query = em.createQuery(queryString, Article.class); 
query.setParameter("newsGroupParam", fullNewsgroupName); 
List<Article> results = query.getResultList();

不要寫在加入JPQL，讓JPA做的工作適合你。

作爲一個額外的提示，你應該總是寫這樣的查詢，以防止SQL注入。

public int getMaxMessageNumber(Folder folder) { 
    int maxMessageNumber = 0; 
    String queryString = "select max(a.messageNumber) from Article a where a.newsgroup.newsgroup = :newsgroup"; 
    Query q = em.createQuery(queryString); 
    q.setParameter("newsgroup", folder.getFullName()); 
    try { 
     maxMessageNumber = (Integer) q.getSingleResult(); 
    } catch (Exception e) { 
     LOG.severe("setting max to zero for " + newsgroup); 
    } 
    LOG.fine(folder.getFullName() + "\t" + maxMessageNumber); 
    return maxMessageNumber; 
}

來源

2012-08-07 13:48:05 siebz0r

翻譯SQL加盟JPQL

回答

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