Question

尝试在@OneToMany和Article之间建立HeaderField关系时，我的映射可能不太正确，导致：

init:
Deleting: /home/thufir/NetBeansProjects/USENET/build/built-jar.properties
deps-jar:
Updating property file: /home/thufir/NetBeansProjects/USENET/build/built-jar.properties
compile:
run:
DEBUG: nntp: newsrc loading /home/thufir/.newsrc
DEBUG: nntp: newsrc load: 1 groups in 31ms
[EL Info]: 2012-07-31 02:05:05.677--ServerSession(8979162)--EclipseLink, version: Eclipse Persistence Services - 2.3.0.v20110604-r9504
[EL Info]: 2012-07-31 02:05:06.778--ServerSession(8979162)--file:/home/thufir/NetBeansProjects/USENET/build/classes/_USENETPU login successful
[EL Warning]: 2012-07-31 02:05:06.903--ServerSession(8979162)--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.HEADERFIELD' doesn't exist
Error Code: 1146
Call: ALTER TABLE HEADERFIELD DROP FOREIGN KEY FK_HEADERFIELD_ARTICLE_ID
Query: DataModifyQuery(sql="ALTER TABLE HEADERFIELD DROP FOREIGN KEY FK_HEADERFIELD_ARTICLE_ID")
[EL Warning]: 2012-07-31 02:05:06.916--ServerSession(8979162)--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]: 2012-07-31 02:05:07.033--ServerSession(8979162)--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")
[EL Warning]: 2012-07-31 02:05:07.122--ServerSession(8979162)--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 'HEADERFIELD'
Error Code: 1051
Call: DROP TABLE HEADERFIELD
Query: DataModifyQuery(sql="DROP TABLE HEADERFIELD")
[EL Warning]: 2012-07-31 02:05:08.921--UnitOfWork(26970615)--java.lang.IllegalStateException: During synchronization a new object was found through a relationship that was not marked cascade PERSIST: null.
Jul 31, 2012 2:05:08 AM net.bounceme.dur.usenet.driver.Main main
SEVERE: null
javax.persistence.RollbackException: java.lang.IllegalStateException: During synchronization a new object was found through a relationship that was not marked cascade PERSIST: null.
    at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commitInternal(EntityTransactionImpl.java:102)
    at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commit(EntityTransactionImpl.java:63)
    at net.bounceme.dur.usenet.driver.Main.persistArticle(Main.java:67)
    at net.bounceme.dur.usenet.driver.Main.<init>(Main.java:43)
    at net.bounceme.dur.usenet.driver.Main.main(Main.java:24)
Caused by: java.lang.IllegalStateException: During synchronization a new object was found through a relationship that was not marked cascade PERSIST: null.
    at org.eclipse.persistence.internal.sessions.RepeatableWriteUnitOfWork.discoverUnregisteredNewObjects(RepeatableWriteUnitOfWork.java:302)
    at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.calculateChanges(UnitOfWorkImpl.java:695)
    at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.commitToDatabaseWithChangeSet(UnitOfWorkImpl.java:1482)
    at org.eclipse.persistence.internal.sessions.RepeatableWriteUnitOfWork.commitRootUnitOfWork(RepeatableWriteUnitOfWork.java:265)
    at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.commitAndResume(UnitOfWorkImpl.java:1135)
    at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commitInternal(EntityTransactionImpl.java:84)
    ... 4 more

[EL Info]: 2012-07-31 02:05:09.332--ServerSession(8979162)--file:/home/thufir/NetBeansProjects/USENET/build/classes/_USENETPU logout successful
BUILD SUCCESSFUL (total time: 9 seconds)

文章：

package net.bounceme.dur.usenet.model;

import java.io.Serializable;
import java.util.AbstractMap.SimpleEntry;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.mail.Header;
import javax.mail.Message;
import javax.mail.MessagingException;
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 String subject;
    @OneToMany(mappedBy = "article", cascade = CascadeType.PERSIST)
    private List<HeaderField> headerFields = new ArrayList<>();

    public Article() {
    }

    public Article(Message message) {
        try {
            subject = message.getSubject();
            Enumeration e = message.getAllHeaders();

            while (e.hasMoreElements()) {
                Header header = (Header) e.nextElement();
                @SuppressWarnings("unchecked")
                SimpleEntry nameValue = new SimpleEntry(header.getName(), header.getValue());
                HeaderField headerField = new HeaderField(nameValue);
                headerFields.add(headerField);
            }
        } catch (MessagingException ex) {
            Logger.getLogger(Article.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    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 subject;
    }

    public String getSubject() {
        return subject;
    }

    public void setSubject(String subject) {
        this.subject = subject;
    }
}

HeaderField：

package net.bounceme.dur.usenet.model;

import java.io.Serializable;
import java.util.AbstractMap.SimpleEntry;
import java.util.logging.Logger;
import javax.persistence.*;

@Entity
public class HeaderField implements Serializable {

    private static final long serialVersionUID = 1L;
    private static final Logger LOG = Logger.getLogger(HeaderField.class.getName());
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @ManyToOne
    private Article article = new Article();
    @Column
    private String headerName;
    @Column
    private String headerValue;

    public HeaderField() {
    }

    public HeaderField(SimpleEntry nameValue) {
        headerName = nameValue.getKey().toString();
        headerValue = nameValue.getValue().toString();
    }

    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 HeaderField)) {
            return false;
        }
        HeaderField other = (HeaderField) 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 "\n\nheaderName\t" + headerName + "\nheaderValue\t" + headerValue;
    }

    public String getHeaderName() {
        return headerName;
    }

    public void setHeaderName(String headerName) {
        this.headerName = headerName;
    }

    public String getHeaderValue() {
        return headerValue;
    }

    public void setHeaderValue(String headerValue) {
        this.headerValue = headerValue;
    }
}

实体已更新，以反映使用CascadeType.PERSIST的建议，似乎可以修复该特定错误消息。我正在努力生成一个更有用的日志来跟踪发生的事情。

Answer 1

您可能做的是创建了Article的新实例以及HeaderField的一些新实例。然后，HeaderField的这些实例与Article相关联。

之后尝试持久化文章失败，因为如错误消息所示，它引用新对象并且关系未标记为PERSIST。此外，根据您的日志，这些HeaderField实例没有设置 headerName 和 headerValue 。

您有两种选择：

还通过em.persist

使用以下

级联持续操作从Article到HeaderFields

OneToMany(mappedBy = "article", cascade = CascadeType.PERSIST)  
private List<HeaderField> someOrAllHeaderFields = new ArrayList<>();

此外，您不应该删除no-arg构造函数。 JPA实现在创建实例时始终调用此构造函数。

但是你可以使no-arg构造函数受到保护。在JPA 2.0规范中，用以下词语表示：

实体类必须具有无参数构造函数。实体类可以还有其他建设者。 no-arg构造函数必须是公共的或受保护。

Answer 2

只需在您的关系中添加CascadeType.ALL

OneToMany(mappedBy = "article", cascade = CascadeType.ALL)  
private List<HeaderField> someOrAllHeaderFields = new ArrayList<>();

Answer 3

我删除了层叠属性，它对我有用：

OneToMany(mappedBy = "article")  
private List<HeaderField> someOrAllHeaderFields = new ArrayList<>();

Answer 4

默认情况下，JPA不提供级联功能。因此，在我的情况下，缺少级联注释，因此我使用@ManyToOne注释对其进行了定义。请与@ManyToOne

一起定义级联类型

例如：

@ManyToOne(cascade = CascadeType.PERSIST)
    private Article article = new Article();

通过未标记为级联PERSIST的关系找到了一个新对象

4 个答案: