Develop Reference

what is gradle missing to map hibernate?

I have unittest to my java project.
My code uses hibernate.
When i run the test using junit - everything passes.
When I run the test using gradle - I get a mapping error:
Caused by: org.hibernate.MappingException: Unknown entity: linqmap.users.interfaces.model.UserRecord
and the class:
#Entity
#Table(name = "users")
public class UserRecord implements Serializable {
private static final long serialVersionUID = 1L;
public static short CLASS_VERSION = 3;
#Transient
public short objectVersion = CLASS_VERSION;
#Id #GeneratedValue(strategy=GenerationType.IDENTITY)
#Column(name = "id")
public long ID;
#Column(name = "user_name")
public String userName;
#Column(name = "email")
public String email;
#Column(name = "full_name") // will be deprecated in the future
public String fullName;
#Column(name = "password")
public String password;
and a config file:
<persistence 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"
version="1.0">
<persistence-unit name="UsersDB">
<!-- The provider only needs to be set if you use several JPA providers <provider>org.hibernate.ejb.HibernatePersistence</provider> -->
<properties>
<!-- Scan for annotated classes and Hibernate mapping XML files -->
<property name="hibernate.archive.autodetection" value="class, hbm" />
<!-- SQL stdout logging <property name="hibernate.show_sql" value="true"/> <property name="hibernate.format_sql" value="true"/>
<property name="use_sql_comments" value="true"/> -->
<property name="hibernate.connection.driver_class" value="org.postgresql.Driver" />
<property name="hibernate.connection.url" value="dbc:postgresql://localhost:9992/israel" />
what can be missing in gradle?

I think the problem is not really with gradle. It's with the fact that the JPA spec stupidly requires that the classes of the entities are in the same jar/directory as the persistence.xml file. And since Gradle doesn't store the "compiled" resources in the same output directory as the compiled classes, Hibernate doesn't find the mapped entities.
Add this line to your gradle build, and it will probably be fine
sourceSets.main.output.resourcesDir = sourceSets.main.output.classesDir

JPA: java.lang.IllegalArgumentException: Not an entity

I wrote a simple Java that uses POJOs, servlets, JSPs. I am using:
Tomcat 7.0.16
Oracle 11g
Oracle Java build 1.6.0_26-b03
I use ivy to resolve my dependencies:
<dependency org="oracle" name="ojdbc6" rev="11g" conf="default -> default" />
<dependency org="org.hibernate" name="hibernate-commons-annotations" rev="3.2.0.Final" conf="compile -> runtime" />
<dependency org="org.hibernate" name="hibernate-annotations" rev="3.5.6-Final" conf="default -> runtime" />
<dependency org="org.hibernate" name="hibernate-core" rev="3.6.5.Final" conf="default -> runtime" />
<dependency org="org.hibernate" name="hibernate-validator" rev="4.0.2.GA" conf="runtime -> runtime" />
<dependency org="org.hibernate.javax.persistence" name="hibernate-jpa-2.0-api" rev="1.0.1.Final" conf="compile -> default" />
<dependency org="org.hibernate" name="hibernate-entitymanager" rev="3.6.5.Final" conf="compile -> default" />
My POJO Vehicle contains the following annotations:
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Version;
#Entity
public class Vehicle implements Serializable{
/**
*
*/
private static final long serialVersionUID = 8560417193012227968L;
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
private Long identifier;
private String serialNumber;
private String model;
private String manufacturer;
private int year;
private String condition;
#Version
private long version;
public Vehicle(){
}
When I run my code, I get the following:
2013-10-28 11:40:50 ERROR SqlVehicleService:42 - java.lang.IllegalArgumentException: Not an entity: class com.foo.demos.car.model.Vehicle
java.lang.IllegalArgumentException: Not an entity: class com.foo.demos.car.model.Vehicle
at org.hibernate.ejb.metamodel.MetamodelImpl.entity(MetamodelImpl.java:160)
at org.hibernate.ejb.criteria.QueryStructure.from(QueryStructure.java:138)
at org.hibernate.ejb.criteria.CriteriaQueryImpl.from(CriteriaQueryImpl.java:179)
at com.foo.demos.car.impl.SqlVehicleService.getVehicles(SqlVehicleService.java:37)
at org.apache.jsp.secured.vehicles_jsp._jspService(vehicles_jsp.java:194)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:419)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:389)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:572)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:563)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:403)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:301)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:162)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:309)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
My persistence.xml does not contain any information about Vehicle. My understanding is that annotations are enough. Is that correct?
<?xml version="1.0" encoding="UTF-8"?>
<persistence 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"
version="1.0">
<persistence-unit name="cardemo">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<!-- the JNDI data source -->
<non-jta-data-source>java:comp/env/jdbc/cardemo</non-jta-data-source>
<properties>
<property name="javax.persistence.validation.mode" value="NONE" />
<!-- if this is true, hibernate will print (to stdout) the SQL it executes,
so you can check it to ensure it"s not doing anything crazy -->
<property name="hibernate.show_sql" value="true" />
<property name="hibernate.format_sql" value="true" />
<!-- since most database servers have slightly different versions of the
SQL, Hibernate needs you to choose a dialect so it knows the subtleties of
talking to that server -->
<property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect" />
<!-- this tell Hibernate to update the DDL when it starts, very useful
for development, dangerous in production -->
<property name="hibernate.hbm2ddl.auto" value="update" />
</properties>
</persistence-unit>
</persistence>
I obviously overlooked something. What's that? What am I missing?

My persistence.xml does not contain any information about Vehicle. My understanding is that annotations are enough. Is that correct?
No, it's not. The entities must be listed in the persistence.xml file, under the persistence-unit element:
<class>com.foo.demos.car.model.Vehicle</class>

You need to give a hint to where the persistent entities can be found. I normally configure via Spring so don't have the exact info required however look here for some further discussion.
Do I need <class> elements in persistence.xml?

you can specify your entity locations via <property name="packagesToScan" value="" /> in the persistence.xml

My problem was that I created a SessionFactory like this:
Configuration configuration = new Configuration();
configuration.configure();
serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
sessionFactory = configuration.buildSessionFactory(serviceRegistry);
instead of like this:
Configuration configuration = new Configuration();
configuration.configure();
sessionFactory = configuration.buildSessionFactory();
When I replaced the former with the later, it worked! So be careful when using SessionFactory's initialization from tutorials.

If you dynamically build your persistence and add properties, you can declare entity classes using 'org.reflections:reflections:0.9.11':
new HibernatePersistenceProvider()
.createContainerEntityManagerFactory(
new javax.persistence.spi.PersistenceUnitInfoImpl(persistenceUnitName),
ImmutableMap.<String, Object>builder()
.put(AvailableSettings.LOADED_CLASSES, getEntities())
.build());
...
private List<Class<?>> getEntities() {
Set<Class<?>> entitiesInPackage = new Reflections("rf.dom.model")
.getTypesAnnotatedWith(Entity.class); // Annotated #Entity
List entities = new ArrayList<>(entitiesInPackage);
return entities;
}

Add packages-to-scan entry in your yml file.
jpa:
default:
packages-to-scan:
- 'com.foo.demos.car.model'
- 'your.entity.package.name'

JPA Entities are not managed / relations not persisted

Setup
I'm Using JPA 1.0, Spring 3.0.6 and hibernate 3.2.1 on JBoss 4.3.2. There are some EJBs which at some point call a DAO which tries to persist two entities.
Problem
The result is quite unexpected: The entities are not managed after calling .persist(entity).
The Funny thing is: A quite similar test app, which uses the same jars containing DAOs, Beans persistence.xml as the server application, persists everything just fine. The beans are managed after calling .persist().
The entities
I have a class Subscriber that has a SubscriberState.
#Entity
#Table(name = "subscriber")
public class Subscriber implements java.io.Serializable {
// all the other stuff
#ManyToOne
#JoinColumn(name = "status")
private SubscriberState state;
}
For legacy reasons the SubscriberState has a relation Subscriber.
#Entity
#Table(name = "subscriber_state")
public class SubscriberState implements java.io.Serializable {
// ...blah
#ManyToOne
#JoinColumn(name = "subscriber", nullable = false)
private Subscriber subscriber;
}
what i do to persist
Now i try to persist a subscriber, it will be unmanaged afer persist():
final Subscriber subscriber = new Subscriber();
// set up...
entityManager.persist(subscriber);
entityManager.contaons(subscriber); //will yield FALSE
Adding a SubscriberState will work. But only one side of the relation will be stored to DB:
SubscriberState subscriberState = new SubscriberState();
subscriberState.setSubscriber(subscriber);
entityManager.persist(subscriberState);
entityManager.merge(subscriber);
where SubscriberState.setSubscriber looks like this:
public void setSubscriber(final Subscriber subscriber) {
this.subscriber = subscriber;
subscriber.setState(this);
}
A look at the database shows me, that the SubscriberState knows it's Subscriber, but the Subscriber does not know it's State.
the config
Here's the (now modified and stripped down) persistence.xml:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
org.hibernate.ejb.HibernatePersistence
java:jdbc/SODS
<properties>
<property name="hibernate.dialect" value="${db.hibernate.dialect}" />
<property name="hibernate.validator.apply_to_ddl" value="false" />
<property name="hibernate.validator.autoregister_listeners" value="false" />
<property name="hibernate.cache.provider_class" value="org.jboss.ejb3.entity.TreeCacheProviderHook" />
<property name="hibernate.treecache.mbean.object_name" value="jboss.cache:service=EJB3EntityTreeCache" />
<property name="jboss.entity.manager.jndi.name" value="java:/SOEntityManager-${app.version}" />
<property name="jboss.entity.manager.factory.jndi.name" value="java:/SOEntityManagerFactory-${app.version}" />
<property name="hibernate.transaction.factory_class" value="org.hibernate.transaction.JTATransactionFactory" />
<property name="hibernate.transaction.manager_lookup_class" value="org.hibernate.transaction.JBossTransactionManagerLookup" />
</properties>
<class>com.stackoverflow.some.classes.i.cant.show.Here</class>
and here are the relevant parts of my spring context:
<context:annotation-config />
<tx:annotation-driven transaction-manager="transactionManager" proxy-target-class="true" />
<jee:jndi-lookup id="entityManagerFactory" jndi-name="java:/SOEntityManagerFactory-${app.version}" />
<jee:jndi-lookup id="entityManager" jndi-name="java:/SOEntityManager-${app.version}" />
<jee:jndi-lookup id="soDataSource" jndi-name="java:jdbc/SODS" />
<bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager" />
<bean id="jdbcTemplate" class="org.springframework.jdbc.core.simple.SimpleJdbcTemplate">
<constructor-arg ref="soDataSource" />
</bean>
<context:component-scan base-package="blah - secret" />
<import resource="daoContext.xml" />
</beans>
Any ideas, why this config won't work?

I don't see use of #Transaction in your DAO or service layer
Adding a SubscriberState will work. But only one side of the relation will be stored to DB
You should use cascade option in
#ManyToOne(cascade = CascadeType.PERSIST)
#JoinColumn(name = "subscriber", nullable = false)
private Subscriber subscriber;
This will save both side of the relationship in persist operation
Also what I see is two unidirectional relationship, not one bidireccional, try to use mappedBy
#ManyToOne
#JoinColumn(name = "status")
private SubscriberState state;
Unless that is not what you want, but you should reconsider your design to made one side OneToMany and the other side ManyToOne, use mappedBy to define the source (owner) of the relationship

This happened to my application, JPA with MySQL. Load the appropriate database driver class in the property file.

JPA, Spring and ObjectDB not updating

I am quite a newbie to Spring JPA in cooperation with ObjectDB database, but I have encountered a problem that I cannot work out.
I have an application written with the mentioned technologies and it works OK, it persists new entities etc. (thus I think there is no problem with the configuration beans), except for updating even the simplest OneToMany/ManyToOne relations. Those updates are not persisted to the database and I cannot figure out why. Here's the snippet of my code:
Entity Team (1:N):
#Entity
public class Team implements Serializable {
...
List<Player> squad;
...
#OneToMany(mappedBy="team", cascade=CascadeType.PERSIST)
public List<Player> getSquad() {
return squad;
}
...
}
Entity Player (N:1)
#Entity
public class Player implements Serializable {
...
private Team team;
...
#ManyToOne
public Team getTeam() {
return team;
}
...
}
Here is a snippet from controller using both DAO objects and the problem:
public ModelAndView addPlayer(HttpServletRequest request, HttpServletResponse response) throws Exception {
...
Team t = teamDao.getTeamById(1); // retrieves an object with ID=1
Player p = playerDao.getPlayerById(1); // retrieves a player with ID=1
t.getSquad().add(p); // adds a player to the squad -> working fine but does not persist
System.out.println("Size of squad: " + t.getSquad().size()); // the player is there
...
return new ModelAndView("index.jsp", "team", t);
}
When I try to list all players in the team inside the index.jsp page or try to add another player the same way, the squad is always empty - nothing persisted to the database. Neither the team object, nor the player object. What do I do wrong?
Any help would be appreciated. Thanks.
EDIT: here is my 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="NewPU" transaction-type="RESOURCE_LOCAL">
<provider>com.objectdb.jpa.Provider</provider>
<properties>
<property name="javax.persistence.jdbc.url" value="C:/file.odb" />
<property name="javax.persistence.jdbc.user" value="admin"/>
<property name="javax.persistence.jdbc.password" value="admin"/>
</properties>
</persistence-unit>
P.S. The absolute path "C:/file.odb" is only for demonstration purposes.
and here is Spring configuration:
<mvc:annotation-driven />
<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="persistenceUnitName" value="NewPU" />
<property name="loadTimeWeaver">
<bean class="org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver" />
</property>
</bean>
<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="entityManagerFactory"/>
</bean>
<tx:annotation-driven transaction-manager="transactionManager" />

CascadeType.PERSIST cascades the persistens of a new object but you load a player from the database and attach the player to your team. If you want to cascade that you have to add the CascadeType.MERGE
cascade = {CascadeType.PERSIST, CascadeType.MERGE}
You may have a look at CascadeType.ALL.

JPA exception: Object: ... is not a known entity type

I'm new to JPA and I'm having problems with the autogeneration of primary key values.
I have the following entity:
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 + "]";
}
}
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();
}
This is my persistence unit:
<?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>
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:...)
What am I missing?

I ran into this same problem using NetBeans IDE 6.9.
Apparently, this is a known issue.
See
http://wiki.eclipse.org/EclipseLink/Development/JPA_2.0/metamodel_api#DI_101:_20100218:_Descriptor.javaClass_is_null_on_a_container_EM_for_a_specific_case.
Also see http://netbeans.org/bugzilla/show_bug.cgi?id=181068.
I added the last line below to persistence.xml and it fixed it for me.
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<!-- Add the following to work around exception issue -->
<exclude-unlisted-classes>false</exclude-unlisted-classes>

As Charles pointed out in his answer, the problem is not the id generation, but the persistence layer not finding the entity.
As you, I am also new to JPA. I have tried to write a "Hello World" JPA application using org.eclipse.persistence.jpa.PersistenceProvider when I got this error. The mentioned workaround also worked for me. Moreover, through trial-error I also found that to declare your entities, you must always anotate #entity in each entity and:
if you set exclude-unlisted-classes to true, you also have to list the entities within class elements in your persistence.xml
if you set exclude-unlisted-classes to false the persistence layer can find the entities regardles of the class element in your persistence.xml.

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"/>
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.
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>
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>
With these settings your code ran as expected.

I use this syntax rather than type AUTO
#javax.persistence.Id
#javax.persistence.GeneratedValue(strategy = GenerationType.IDENTITY)
Then, I use the simple type "long" for ID's with a lowercase l :
private long taskID;
This may be unrelated, but I also specify a different table name for my entities:
#javax.persistence.Entity(name = "Tasks")
public class Task implements Serializable

I ran into the same exception, when deploying web applications to GlassFish v3 (which uses EclipseLink as its JPA provider). I am not sure it's the same scenario as above - but the explanation for this bug in my case might help others :-) - turns out there's a bug in EclipseLink, when running under OSGi (which is the case in GlassFish), which leads EclipseLink to hold on to an "old" version of the entity class when re-deploying, resulting in this exception. The bug report is here.

As far as I know, whenever I get this error, I just re-start glassfish. Works everytime.

if you are only getting this error in junit
try adding this in persistence.xml
<jar-file>file:../classes</jar-file>

You could try and leave the definition out of the persistnce.xml The Persistence provider should than scan all classes in the classpath for #Entity annotations.

I also have to add one other item to my persistence.xml when changing class/table defs so that the EM knows to build/update tables:
<property name="openjpa.jdbc.SynchronizeMappings" value="buildSchema(SchemaAction=&apos;refresh&apos;)"/>
If I want a fresh start, I instead use:
<!--<property name="openjpa.jdbc.SynchronizeMappings"
value="buildSchema(SchemaAction='dropDB,add')"/>
-->
I noticed that in your persistence.xml schema management is only set to "create tables" as opposed to drop/create, or update

Check the class output folder of eclipse, sometimes you change the xml and it was not updated.

The combination of deployment from within NetBeans 8.2 on Glassfish 4.1 on a Maven project with the "Debug" function of a project can cause an outdated version to be re-deployed (unclear where the fault lies).
Stop GlassFish, delete [glassfish base]/glassfish/domains/[domain name]/generated/, restart and redeploy.