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如果发生 NoResultException
,我该如何实例化并持久化 Newsgroup
实体?
package net.bounceme.dur.usenet.driver;
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();
public void persistArticle(Message message, Folder folder) {
//do all the persistence here?
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.info("found " + query.getSingleResult()); //ok
} catch (javax.persistence.NoResultException e) {
LOG.info(e + "\ncould not find " + fullNewsgroupName); //ok
newsgroup = new Newsgroup(folder);
//it seems like the persist statement never executes...
em.persist(newsgroup);
} catch (NonUniqueResultException e) {
LOG.info("\nshould never happen\t" + fullNewsgroupName); //not ok, should never execute
}
//need some mechanism to ensure that newsgroup is never a null reference
Article article = new Article(message, newsgroup);
em.persist(article); //never seems to execute..
}
public void close() {
em.close();
emf.close();//necessary?
}
}
现在,似乎一遍又一遍,找不到查询的结果:
run:
DEBUG: nntp: newsrc loading /home/thufir/.newsrc
DEBUG: nntp: newsrc load: 5 groups in 30ms
Aug 03, 2012 6:04:47 PM net.bounceme.dur.usenet.driver.FetchBean <init>
INFO: [gwene.com.androidcentral, gwene.com.blogspot.emacsworld, gwene.com.blogspot.googlecode, gwene.com.blogspot.googlereader, gwene.com.economist]
[EL Info]: 2012-08-03 18:04:51.277--ServerSession(28034142)--EclipseLink, version: Eclipse Persistence Services - 2.3.0.v20110604-r9504
[EL Info]: 2012-08-03 18:04:52.417--ServerSession(28034142)--file:/home/thufir/NetBeansProjects/USENET/build/classes/_USENETPU login successful
[EL Warning]: 2012-08-03 18:04:52.557--ServerSession(28034142)--Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.0.v20110604-r9504): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Table 'usenet.ARTICLE' doesn't exist
Error Code: 1146
Call: ALTER TABLE ARTICLE DROP FOREIGN KEY FK_ARTICLE_NEWSGROUP_ID
Query: DataModifyQuery(sql="ALTER TABLE ARTICLE DROP FOREIGN KEY FK_ARTICLE_NEWSGROUP_ID")
[EL Warning]: 2012-08-03 18:04:52.572--ServerSession(28034142)--Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.0.v20110604-r9504): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown table 'ARTICLE'
Error Code: 1051
Call: DROP TABLE ARTICLE
Query: DataModifyQuery(sql="DROP TABLE ARTICLE")
[EL Warning]: 2012-08-03 18:04:52.65--ServerSession(28034142)--Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.0.v20110604-r9504): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown table 'NEWSGROUP'
Error Code: 1051
Call: DROP TABLE NEWSGROUP
Query: DataModifyQuery(sql="DROP TABLE NEWSGROUP")
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.androidcentral
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.androidcentral
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.androidcentral
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.androidcentral
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.androidcentral
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.androidcentral
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.androidcentral
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.androidcentral
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.blogspot.emacsworld
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.blogspot.googlecode
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.blogspot.googlecode
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.blogspot.googlecode
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.blogspot.googlecode
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.blogspot.googlecode
Aug 03, 2012 6:04:54 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.blogspot.googlecode
Aug 03, 2012 6:04:55 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
[EL Info]: 2012-08-03 18:04:55.344--ServerSession(28034142)--file:/home/thufir/NetBeansProjects/USENET/build/classes/_USENETPU logout successful
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.blogspot.googlecode
Aug 03, 2012 6:04:55 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.blogspot.googlecode
Aug 03, 2012 6:04:55 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.economist
Aug 03, 2012 6:04:55 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.economist
Aug 03, 2012 6:04:55 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.economist
Aug 03, 2012 6:04:55 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.economist
Aug 03, 2012 6:04:55 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.economist
Aug 03, 2012 6:04:55 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.economist
Aug 03, 2012 6:04:55 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.economist
Aug 03, 2012 6:04:55 PM net.bounceme.dur.usenet.driver.DatabaseUtils persistArticle
INFO: javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
could not find gwene.com.economist
Aug 03, 2012 6:04:55 PM net.bounceme.dur.usenet.driver.FetchBean <init>
INFO: **************************done
BUILD SUCCESSFUL (total time: 11 seconds)
当不存在唯一的 Newsgroup
时,如何确保将新实体持久保存到数据库中?如果不是结果,那至少是代码的意图。
新闻组:
package net.bounceme.dur.usenet.model;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import java.util.logging.Logger;
import javax.mail.Folder;
import javax.persistence.*;
@Entity
public class Newsgroup implements Serializable {
private static final long serialVersionUID = 1L;
private static final Logger LOG = Logger.getLogger(Newsgroup.class.getName());
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column //@Unique @UniqueConstraint interface..?
private String newsgroup;
@OneToMany(mappedBy = "newsgroup", cascade = CascadeType.PERSIST)
private Set<Article> articles = new HashSet<>();
public Newsgroup() {
//should not create a newsgroup without a Folder
}
public Newsgroup(Folder folder) {
newsgroup = folder.getFullName();//if row already exists, then what?
LOG.fine(newsgroup);
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@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 newsgroup;
}
}
和文章:
package net.bounceme.dur.usenet.model;
import java.io.Serializable;
import java.util.logging.Logger;
import javax.mail.Message;
import javax.persistence.*;
@Entity
public class Article implements Serializable {
private static final long serialVersionUID = 1L;
private static final Logger LOG = Logger.getLogger(Article.class.getName());
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column
private int messageNumber;
@ManyToOne(cascade = CascadeType.PERSIST)
private Newsgroup newsgroup;
public Article() {
}
public Article(Message message, Newsgroup newsgroup) {
messageNumber = message.getMessageNumber();
this.newsgroup = newsgroup;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@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 "\nmessageNumber\t" + messageNumber;
}
public int getMessageNumber() {
return messageNumber;
}
public void setMessageNumber(int messageNumber) {
this.messageNumber = messageNumber;
}
}
最佳答案
引用“Pro JPA 2”中的 Keith 和 Schincariol:
If a transaction is not present, then either the modifying operation will throw an exception or the change will simply never be persisted to the data store.
使用 EntityManager em
确保您希望持久化的交互在事务的上下文中:
public void persistArticle(Message message, Folder folder) {
em.getTransaction().begin();
try {
// your code goes here; possibly current body of persistArticle(..)
em.getTransaction().commit();
} catch (final RuntimeException e) {
if (em.getTransaction().isActive()) {
em.getTransaction().rollback();
}
throw e;
}
}
您很快就会发现这是通用的样板代码。考虑使用 decorator :
DatabaseUtils
提供的服务/方法。DatabaseUtils
实现该接口(interface)。DataUtilsServices
(装饰器)。它的实现将包含管理事务的代码,其中工作代码(“您的代码放在此处”)成为对 DatabaseUtils
实例上相同方法的调用。现在使用装饰器将“工作人员”与“事务服务”分开,这将使您将来可以轻松进入 Java EE、Spring 或其他为您管理事务的容器框架。例如,包含所有样板的 DatabaseUtilsServices
很可能成为 EJB 装饰器的一部分:
@Override
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public void persistArticle(Message message, Folder folder) {
return databaseUtils.persistArticle(message, folder);
}
关于java - 为什么不保留新实体?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/11805116/
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