How我为下面的查询设置参数：
实体：
package net.bounceme.dur.usenet.model;
import java.io.Serializable;
import java.util.logging.Logger;
import javax.mail.Folder;
import javax.mail.Message;
import javax.persistence.*;
import net.bounceme.dur.usenet.driver.FetchBean;
@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, Folder folder) {
messageNumber = message.getMessageNumber();
EntityManagerFactory emf;
EntityManager em;
emf = Persistence.createEntityManagerFactory("USENETPU");
em = emf.createEntityManager();
String ng = folder.getFullName();
Query query = em.createQuery("SELECT n FROM Newsgroup n WHERE n.newsgroup = :newsgroup", Newsgroup.class);
Newsgroup result = (Newsgroup) query.getSingleResult();
newsgroup = (result == null) ? new Newsgroup(folder) : result;
}
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;
}
}
堆栈追踪：
run:
DEBUG: nntp: newsrc loading /home/thufir/.newsrc
DEBUG: nntp: newsrc load: 5 groups in 39ms
[EL Info]: 2012-08-03 03:26:30.737--ServerSession(13970219)--EclipseLink, version: Eclipse Persistence Services - 2.3.0.v20110604-r9504
[EL Info]: 2012-08-03 03:26:31.815--ServerSession(13970219)--file:/home/thufir/NetBeansProjects/USENET/build/classes/_USENETPU login successful
Aug 03, 2012 3:26:32 AM 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]
Aug 03, 2012 3:26:32 AM net.bounceme.dur.usenet.driver.FetchBean <init>
INFO: Google helping out newcomers with Nexus 7 getting started video
Aug 03, 2012 3:26:33 AM net.bounceme.dur.usenet.driver.FetchBean main
SEVERE: null
java.lang.IllegalStateException: Query argument newsgroup not found in the list of parameters provided during query execution.
at org.eclipse.persistence.internal.jpa.EJBQueryImpl.processParameters(EJBQueryImpl.java:829)
at org.eclipse.persistence.internal.jpa.EJBQueryImpl.executeReadQuery(EJBQueryImpl.java:406)
at org.eclipse.persistence.internal.jpa.EJBQueryImpl.getSingleResult(EJBQueryImpl.java:773)
at net.bounceme.dur.usenet.model.Article.<init>(Article.java:34)
at net.bounceme.dur.usenet.driver.FetchBean.<init>(FetchBean.java:41)
at net.bounceme.dur.usenet.driver.FetchBean.main(FetchBean.java:21)
BUILD SUCCESSFUL (total time: 13 seconds)
对于新闻组名称，命名参数应该是ng，但我似乎无法获得在Newsgroup.newsgroup字段中查询该字符串的语法。如何修复查询？
------------- ---------------- EDIT
新追踪：
run:
DEBUG: nntp: newsrc loading /home/thufir/.newsrc
DEBUG: nntp: newsrc load: 5 groups in 30ms
[EL Info]: 2012-08-03 03:57:03.647--ServerSession(33288487)--EclipseLink, version: Eclipse Persistence Services - 2.3.0.v20110604-r9504
[EL Info]: 2012-08-03 03:57:04.691--ServerSession(33288487)--file:/home/thufir/NetBeansProjects/USENET/build/classes/_USENETPU login successful
Aug 03, 2012 3:57:05 AM 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]
Aug 03, 2012 3:57:05 AM net.bounceme.dur.usenet.driver.FetchBean <init>
INFO: Google helping out newcomers with Nexus 7 getting started video
Aug 03, 2012 3:57:06 AM net.bounceme.dur.usenet.driver.FetchBean main
SEVERE: null
java.lang.IllegalArgumentException: You have attempted to set a parameter value using a name of gwene.com.androidcentral that does not exist in the query string SELECT n FROM Newsgroup n WHERE n.newsgroup = :ng.
at org.eclipse.persistence.internal.jpa.EJBQueryImpl.setParameterInternal(EJBQueryImpl.java:1256)
at org.eclipse.persistence.internal.jpa.EJBQueryImpl.setParameter(EJBQueryImpl.java:1138)
at org.eclipse.persistence.internal.jpa.EJBQueryImpl.setParameter(EJBQueryImpl.java:81)
at net.bounceme.dur.usenet.model.Article.<init>(Article.java:34)
at net.bounceme.dur.usenet.driver.FetchBean.<init>(FetchBean.java:41)
at net.bounceme.dur.usenet.driver.FetchBean.main(FetchBean.java:21)
BUILD SUCCESSFUL (total time: 17 seconds)
代码段：
String ng = folder.getFullName();
Query query = em.createQuery("SELECT n FROM Newsgroup n WHERE n.newsgroup = :ng", Newsgroup.class);
query.setParameter(ng, ng); //newsgroup object????
Newsgroup result = (Newsgroup) query.getSingleResult();
LOG.info(result.toString());
newsgroup = (result == null) ? new Newsgroup(folder) : result;
答案 0 :(得分：3)
Query query = em.createQuery("SELECT n FROM Newsgroup n WHERE n.newsgroup = :newsgroup");
query.setParameter("newsgroup",newsgroup object);
Newsgroup result = (Newsgroup) query.getSingleResult();
答案 1 :(得分：0)
或者您可以使用查询的setString（..）方法：
Query query = em.createQuery("SELECT n FROM Newsgroup n WHERE n.newsgroup = :newsgroup", Newsgroup.class);
query.setString("newsgroup", ng);
Newsgroup result = (Newsgroup) query.getSingleResult();
答案 2 :(得分：0)
对于记录，以下运行：
public Article(Message message, Folder folder) {
messageNumber = message.getMessageNumber();
EntityManagerFactory emf;
EntityManager em;
emf = Persistence.createEntityManagerFactory("USENETPU");
em = emf.createEntityManager();
String ng = folder.getFullName();
TypedQuery<Newsgroup> query = em.createQuery("SELECT n FROM Newsgroup n WHERE n.newsgroup = :newsgroup", Newsgroup.class);
query.setParameter("newsgroup", ng);//newsgroup object
Newsgroup result = query.getSingleResult();
LOG.info(result.toString());
newsgroup = (result == null) ? new Newsgroup(folder) : result;
}
仅出现以下小错误：
run:
DEBUG: nntp: newsrc loading /home/thufir/.newsrc
DEBUG: nntp: newsrc load: 5 groups in 12ms
[EL Info]: 2012-08-03 04:21:28.427--ServerSession(18852961)--EclipseLink, version: Eclipse Persistence Services - 2.3.0.v20110604-r9504
[EL Info]: 2012-08-03 04:21:29.496--ServerSession(18852961)--file:/home/thufir/NetBeansProjects/USENET/build/classes/_USENETPU login successful
Aug 03, 2012 4:21:30 AM 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]
Aug 03, 2012 4:21:30 AM net.bounceme.dur.usenet.driver.FetchBean <init>
INFO: Google helping out newcomers with Nexus 7 getting started video
Aug 03, 2012 4:21:31 AM net.bounceme.dur.usenet.driver.FetchBean main
SEVERE: null
javax.persistence.NoResultException: getSingleResult() did not retrieve any entities.
at org.eclipse.persistence.internal.jpa.EJBQueryImpl.throwNoResultException(EJBQueryImpl.java:1310)
at org.eclipse.persistence.internal.jpa.EJBQueryImpl.getSingleResult(EJBQueryImpl.java:778)
at net.bounceme.dur.usenet.model.Article.<init>(Article.java:35)
at net.bounceme.dur.usenet.driver.FetchBean.<init>(FetchBean.java:41)
at net.bounceme.dur.usenet.driver.FetchBean.main(FetchBean.java:21)
BUILD SUCCESSFUL (total time: 14 seconds)
我发现tutorial并不是非常有用，但我认为至少解决了语法问题。