Question

您好我正在撰写我的第一个JPA项目之一，而且我在这个领域有点新手，所以请尽量简化内容:) 这是实体之一

package model;

import java.io.Serializable;
import java.sql.Date;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.xml.bind.annotation.XmlRootElement;

@Entity

public class Speaker implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    @Id @GeneratedValue(strategy=GenerationType.AUTO)
    private int id;
    private String name;
    private Date dob;
    private String skills;
    @OneToMany(mappedBy="event",cascade={CascadeType.ALL})
    private Set <Session> speakerSessions;

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }
    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }
    /**
     * @return the dob
     */
    public Date getDob() {
        return dob;
    }
    /**
     * @param dob the dob to set
     */
    public void setDob(Date dob) {
        this.dob = dob;
    }
    /**
     * @return the skills
     */
    /**
     * @return the skills
     */
    public String getSkills() {
        return skills;
    }
    /**
     * @param skills the skills to set
     */
    public void setSkills(String skills) {
        this.skills = skills;
    }
    /**
     * @return the id
     */
    public int getId() {
        return id;
    }
    /**
     * @param id the id to set
     */

}

这里是被抛出的异常

   Exception in thread "main" javax.persistence.PersistenceException: Exception [EclipseLink-28019] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.EntityManagerSetupException
Exception Description: Deployment of PersistenceUnit [test] failed. Close all factories for this PersistenceUnit.
Internal Exception: Exception [EclipseLink-0] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.IntegrityException
Descriptor Exceptions: 
---------------------------------------------------------

Exception [EclipseLink-93] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: The table [EVENT] is not present in this descriptor.
Descriptor: RelationalDescriptor(model.Speaker --> [DatabaseTable(SPEAKER)])

Exception [EclipseLink-41] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: A non-read-only mapping must be defined for the sequence number field.
Descriptor: RelationalDescriptor(model.Speaker --> [DatabaseTable(SPEAKER)])

Runtime Exceptions: 
---------------------------------------------------------

    at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.createDeployFailedPersistenceException(EntityManagerSetupImpl.java:816)
    at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.deploy(EntityManagerSetupImpl.java:756)
    at org.eclipse.persistence.internal.jpa.EntityManagerFactoryDelegate.getAbstractSession(EntityManagerFactoryDelegate.java:204)
    at org.eclipse.persistence.internal.jpa.EntityManagerFactoryDelegate.createEntityManagerImpl(EntityManagerFactoryDelegate.java:304)
    at org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManagerImpl(EntityManagerFactoryImpl.java:336)
    at org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:302)
    at Test.Tester.main(Tester.java:19)
Caused by: Exception [EclipseLink-28019] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.EntityManagerSetupException
Exception Description: Deployment of PersistenceUnit [test] failed. Close all factories for this PersistenceUnit.
Internal Exception: Exception [EclipseLink-0] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.IntegrityException
Descriptor Exceptions: 
---------------------------------------------------------

Exception [EclipseLink-93] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: The table [EVENT] is not present in this descriptor.
Descriptor: RelationalDescriptor(model.Speaker --> [DatabaseTable(SPEAKER)])

Exception [EclipseLink-41] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: A non-read-only mapping must be defined for the sequence number field.
Descriptor: RelationalDescriptor(model.Speaker --> [DatabaseTable(SPEAKER)])

Runtime Exceptions: 
---------------------------------------------------------

    at org.eclipse.persistence.exceptions.EntityManagerSetupException.deployFailed(EntityManagerSetupException.java:238)
    ... 7 more
Caused by: Exception [EclipseLink-0] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.IntegrityException
Descriptor Exceptions: 
---------------------------------------------------------

Exception [EclipseLink-93] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: The table [EVENT] is not present in this descriptor.
Descriptor: RelationalDescriptor(model.Speaker --> [DatabaseTable(SPEAKER)])

Exception [EclipseLink-41] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: A non-read-only mapping must be defined for the sequence number field.
Descriptor: RelationalDescriptor(model.Speaker --> [DatabaseTable(SPEAKER)])

Runtime Exceptions: 
---------------------------------------------------------

    at org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.initializeDescriptors(DatabaseSessionImpl.java:689)
    at org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.initializeDescriptors(DatabaseSessionImpl.java:625)
    at org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.initializeDescriptors(DatabaseSessionImpl.java:565)
    at org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.postConnectDatasource(DatabaseSessionImpl.java:792)
    at org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.loginAndDetectDatasource(DatabaseSessionImpl.java:736)
    at org.eclipse.persistence.internal.jpa.EntityManagerFactoryProvider.login(EntityManagerFactoryProvider.java:239)
    at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.deploy(EntityManagerSetupImpl.java:681)
    ... 5 more

我几乎没有这方面的经验，所以请提供尽可能详细的信息：）

这是会话实体人员

package model;

import java.io.Serializable;
import java.sql.Date;

import javax.persistence.*;
import javax.xml.bind.annotation.XmlRootElement;

@Entity
@Table (name="session")
@NamedQueries({
@NamedQuery (name="findAllSessionForEvent",query="select e from Session e where e.event.id= :id"),
@NamedQuery (name="findSessionsBySpeakerName",query="select e from Session e where e.speaker.name=':name'"),
@NamedQuery (name="findSpeakerOfSessionBySessionId",query="select e.speaker.name from Session e where e.id=:id")})
@XmlRootElement

public class Session implements Serializable {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    @Id @GeneratedValue(strategy=GenerationType.SEQUENCE)
    private int id;
    private Date date;
    @ManyToOne
    @JoinColumn (name="eventID")
    //@Column(name="eventID")
    private Event event;
    @ManyToOne
    @JoinColumn (name="speakerID")
    //@Column(name="speakerID")
    private Speaker speaker;
    /**
     * @return the date
     */
    public Date getDate() {
        return date;
    }
    /**
     * @param date the date to set
     */
    public void setDate(Date date) {
        this.date = date;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public Speaker getSpeaker() {
        return speaker;
    }
    public void setSpeaker(Speaker speaker) {
        this.speaker = speaker;
    }
    public Event getEvent() {
        return event;
    }
    public void setEvent(Event event) {
        this.event = event;
    }


}

Answer 1

如果你有Session.speaker，为什么Speaker.speakerSessions有 mappedBy = event ???它应该是“扬声器”。 MappedBy基本上说明了关系另一边的字段是什么

Answer 2

您必须在基础数据库中具有正确的架构结构，并且必须在JPA实体中具有正确的映射。

对于正确的架构，您可以从JPA供应商生成架构开始。您可以通过向persistence.xml文件添加一个属性来实现此目的：

如果您使用的是EclipseLink：

<property name="eclipselink.ddl-generation" value="create-tables" />
如果你正在使用Hibernate：

<property name="hibernate.hbm2ddl.auto" value="create" />

使用它们你应该摆脱A non-read-only mapping must be defined for the sequence number field.错误。此错误告诉您JPA提供程序没有从中生成ID的表。

您的第二个错误The table [EVENT] is not present in this descriptor.可能意味着@OneToMany映射到Session的问题。会话是一个实体，是否有正确的@ManyToOne映射回Speaker？

Answer 3

错误说 - ＆＃34;必须为序列号字段定义非只读映射。＆＃34;

尝试为您的＆＃39; Id＆＃39;添加setter。 Speaker.java中的字段

IE中。将此代码添加到Speaker.java -

public void setId(int id) {
    this.id = id;
}

Answer 4

异常说明：此描述符中不存在[EVENT]表。

添加

@Table(name="Schamaname.Tablename")

或

@Table(name = "Tablename", schema = "Schamaname")

为id添加getter和setter。如果你得到NullPointerException初始化id与构造函数

public Speaker (int id) {
    this.id = id
}

或将int更改为Integer，因为int不能是＆＃34; null＆＃34;在java中，但它是主键，它在数据库中永远不应为null。

您可能还需要@NamedQueries。

映射到实体时的JPA异常

4 个答案: