JPA异常:对象:...不是已知的实体类型 [英] JPA exception: Object: ... is not a known entity type
问题描述
我是JPA的新手，我在自动生成主键值时遇到问题.
I'm new to JPA and I'm having problems with the autogeneration of primary key values.
我有以下实体:
package jpatest.entities;
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
@Entity
public class MyEntity implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
private String someProperty;
public String getSomeProperty() {
return someProperty;
}
public void setSomeProperty(String someProperty) {
this.someProperty = someProperty;
}
public MyEntity() {
}
public MyEntity(String someProperty) {
this.someProperty = someProperty;
}
@Override
public String toString() {
return "jpatest.entities.MyEntity[id=" + id + "]";
}
}
以及其他类中的以下主要方法:
and the following main method in other class:
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("JPATestPU");
EntityManager em = emf.createEntityManager();
em.getTransaction().begin();
MyEntity e = new MyEntity("some value");
em.persist(e); /* (exception thrown here) */
em.getTransaction().commit();
em.close();
emf.close();
}
这是我的持久性单元:
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
<persistence-unit name="JPATestPU" transaction-type="RESOURCE_LOCAL">
<provider>oracle.toplink.essentials.PersistenceProvider</provider>
<class>jpatest.entities.MyEntity</class>
<properties>
<property name="toplink.jdbc.user" value="..."/>
<property name="toplink.jdbc.password" value="..."/>
<property name="toplink.jdbc.url" value="jdbc:mysql://localhost:3306/jpatest"/>
<property name="toplink.jdbc.driver" value="com.mysql.jdbc.Driver"/>
<property name="toplink.ddl-generation" value="create-tables"/>
</properties>
</persistence-unit>
</persistence>
执行程序时，在带有正确注释的行中得到以下异常:
When I execute the program I get the following exception in the line marked with the proper comment:
Exception in thread "main" java.lang.IllegalArgumentException: Object: jpatest.entities.MyEntity[id=null] is not a known entity type.
at oracle.toplink.essentials.internal.sessions.UnitOfWorkImpl.registerNewObjectForPersist(UnitOfWorkImpl.java:3212)
at oracle.toplink.essentials.internal.ejb.cmp3.base.EntityManagerImpl.persist(EntityManagerImpl.java:205)
at jpatest.Main.main(Main.java:...)
我想念什么?
推荐答案
TopLink曾经要求您为MySQL明确设置 GenerationType.IDENTITY ，因此请更改它并删除数据库.然后尝试再次运行样本.此外，您可能还想明确设置数据库平台:
TopLink used to require you to explicitly set GenerationType.IDENTITY for MySQL, so change this and drop the database. Then try running your sample again. Further you might also want to explcitly set the database platform:
<property name="toplink.platform.class.name"
value="oracle.toplink.platform.database.MySQL4Platform"/>
我也隐约记得您必须使用其Java代理运行Toplink，以使其能够与资源本地实体管理器一起正常运行.
Also I vaguely remember that you have to run Toplink using its Java agent in order to make it function properly with a resource local entitymanager.
但是，我确实使用EclipseLink成功运行了您的示例(由于Toplink已过时，应该使用该示例).唯一的缺点是我没有方便的MySQL服务器，因此我使用H2来运行它.我使用以下Maven pom.xml来解决依赖关系:
I did however successfully run your example using EclipseLink (which you should use since Toplink is outdated). Only cavat was that I did not have MySQL server handy, so I ran it using H2. I used the following Maven pom.xml to resolve the dependencies:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.randompage</groupId>
<artifactId>sandbox</artifactId>
<packaging>jar</packaging>
<version>1.0</version>
<name>sandbox</name>
<repositories>
<repository>
<id>EclipseLink Repo</id>
<url>http://www.eclipse.org/downloads/download.php?r=1&nf=1&file=/rt/eclipselink/maven.repo</url>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>javax.persistence</groupId>
<artifactId>javax.persistence</artifactId>
<version>2.0-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>org.eclipse.persistence</groupId>
<artifactId>eclipselink</artifactId>
<version>2.0.0</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<version>1.2.130</version>
</dependency>
</dependencies>
</project>
和这个persistence.xml:
and this persistence.xml:
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="JPATestPU" transaction-type="RESOURCE_LOCAL">
<provider>
org.eclipse.persistence.jpa.PersistenceProvider
</provider>
<class>org.randompage.MyEntity</class>
<properties>
<property name="javax.persistence.jdbc.user" value="johndoe"/>
<property name="javax.persistence.jdbc.password" value="secret"/>
<property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
<property name="javax.persistence.jdbc.url" value="jdbc:h2:~/.h2/testdb;FILE_LOCK=NO"/>
<property name="eclipselink.ddl-generation" value="create-tables"/>
<property name="eclipselink.logging.level" value="INFO"/>
</properties>
</persistence-unit>
</persistence>
使用这些设置，您的代码按预期运行.
With these settings your code ran as expected.
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