Excepion: mapping cannot have columns in this context(JPA/OpenJPA OneToMany using single table)

[ping zhang]

I want use JPA(provider:OpenJPA) to implement the funciton of category without level limit, and just using one table like the following, and use the annotation:
[b ]@OneToMany(fetch=FetchType.LAZY)
@JoinColumn(name="pid")[/b]

But there alaway exception when using "org.apache.openjpa.jdbc.meta.MappingTool" to generate schema or access data after created schema manually.
If I remove the two line of @OneToMany and @JoinColumn, things go well.

+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id | varchar(255) | NO | PRI | NULL | |
| name | varchar(255) | YES | | NULL | |
| pid | varchar(255) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+


The code:

package test;

import java.util.List;

import javax.persistence.Basic;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Column;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name = "category")
public class Category {
	@Id
	@GeneratedValue(strategy = GenerationType.AUTO, generator="uuid-hex")
	private String id;
	
	private String pid;
	
	private String name;

[b]	@OneToMany(fetch=FetchType.LAZY)
	@JoinColumn(name="pid")[/b]
	private List <Category> children;
	

	public String getId() {
		return id;
	}

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

	public String getPid() {
		return pid;
	}

	public void setPid(String pid) {
		this.pid = pid;
	}
	
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}


	public void setChildren(List<Category> children) {
		this.children = children;
	}

	public List<Category> getChildren() {
		return children;
	}
}
  

And the Exception:

 78  infosys  INFO   [main] openjpa.Runtime - Starting OpenJPA 1.2.0
Exception in thread "main" <openjpa-1.2.0-r422266:683325 fatal user error> org.apache.openjpa.persistence.ArgumentException:
[b] You have supplied columns for "test.Category.children", but this mapping cannot have columns in this context.[/b]
	at org.apache.openjpa.jdbc.meta.MappingInfo.assertNoSchemaComponents(MappingInfo.java:327)
	at org.apache.openjpa.jdbc.meta.strats.RelationToManyTableFieldStrategy.map(RelationToManyTableFieldStrategy.java:96)
	at org.apache.openjpa.jdbc.meta.strats.RelationCollectionTableFieldStrategy.map(RelationCollectionTableFieldStrategy.java:94)
	at org.apache.openjpa.jdbc.meta.FieldMapping.setStrategy(FieldMapping.java:121)
	at org.apache.openjpa.jdbc.meta.RuntimeStrategyInstaller.installStrategy(RuntimeStrategyInstaller.java:80)
	at org.apache.openjpa.jdbc.meta.FieldMapping.resolveMapping(FieldMapping.java:454)
	at org.apache.openjpa.jdbc.meta.FieldMapping.resolve(FieldMapping.java:419)
	at org.apache.openjpa.jdbc.meta.ClassMapping.resolveMapping(ClassMapping.java:816)
	at org.apache.openjpa.meta.ClassMetaData.resolve(ClassMetaData.java:1629)
	at org.apache.openjpa.meta.MetaDataRepository.processBuffer(MetaDataRepository.java:717)
	at org.apache.openjpa.meta.MetaDataRepository.resolveMapping(MetaDataRepository.java:677)
	at org.apache.openjpa.meta.MetaDataRepository.resolve(MetaDataRepository.java:555)
	at org.apache.openjpa.meta.MetaDataRepository.getMetaData(MetaDataRepository.java:308)
	at org.apache.openjpa.enhance.PCEnhancer.<init>(PCEnhancer.java:248)
	at org.apache.openjpa.enhance.PCEnhancer.<init>(PCEnhancer.java:219)
	at org.apache.openjpa.enhance.PCEnhancer.<init>(PCEnhancer.java:187)
	at org.apache.openjpa.enhance.ManagedClassSubclasser.prepareUnenhancedClasses(ManagedClassSubclasser.java:121)
	at org.apache.openjpa.kernel.AbstractBrokerFactory.loadPersistentTypes(AbstractBrokerFactory.java:310)
	at org.apache.openjpa.kernel.AbstractBrokerFactory.initializeBroker(AbstractBrokerFactory.java:228)
	at org.apache.openjpa.kernel.AbstractBrokerFactory.newBroker(AbstractBrokerFactory.java:190)
	at org.apache.openjpa.kernel.DelegatingBrokerFactory.newBroker(DelegatingBrokerFactory.java:142)
	at org.apache.openjpa.persistence.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:192)
	at org.apache.openjpa.persistence.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:145)
	at org.apache.openjpa.persistence.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:56)
	at test.TestAll.testCreate(TestAll.java:46)
	at test.TestAll.main(TestAll.java:18)
   

Anyone can give me some help? Thanks