映射到實體時的JPA異常

Question

嗨，我正在編寫我的第一個JPA項目之一，我在這個領域有點新手，所以請盡可能地簡化一些東西:)這是其中一個實體

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
     */

}

這是被拋出的異常

   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

我幾乎沒有這方面的經驗，所以請提供盡可能詳細的信息:)

這是會話實體的人

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那么為什么Speaker.speakerSessions有mappedBy = event ??? 它應該是“ 發言者 ”。 MappedBy基本上說明了關系另一邊的字段是什么

Answer 2

您必須在底層數據庫中具有正確的架構結構，並且必須在JPA實體中具有正確的映射。

對於正確的模式，您可以從JPA供應商生成模式開始。 您可以通過向persistence.xml文件添加一個屬性來實現此目的：

• 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" />

使用它們你應該擺脫A non-read-only mapping must be defined for the sequence number field. 錯誤。 此錯誤告訴您JPA提供程序沒有從中生成ID的表。

您的第二個錯誤The table [EVENT] is not present in this descriptor. 可能意味着@OneToMany映射到Session的問題。 Session是一個實體，是否有正確的@ManyToOne映射回Speaker ？

Answer 3

錯誤說 - “必須為序列號字段定義非只讀映射。”

嘗試在Speaker.java中為“Id”字段添加setter

IE瀏覽器。 將此代碼添加到Speaker.java -

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

Answer 4

異常描述：此描述符中不存在表[EVENT]。

加

@Table(name="Schamaname.Tablename")

要么

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

為id添加getter和setter。 如果你得到NullPointerException初始化id與構造函數

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

或者將int更改為Integer，因為int在java中不能為“null”，但是至於它是主鍵，它在數據庫中永遠不應該為null。

您可能還需要@NamedQueries。