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[英]difference of owned one-to-many relationship between GAE/J low level datastore API and DataNucleus JDO
[英]Gae Jdo persistance on one-to-many owned relationship with bidirectional navigation
我正在尝试使用JDO在GAE中保持一对多拥有双向导航的关系。
我手动添加Contact
to User
类,我希望最终Contact
将具有对父User
对象的引用。
org.datanucleus.store.appengine.DatastoreRelationFieldManager.checkForParentSwitch(DatastoreRelationFieldManager.java:204)
User
对象持久性之后,父引用不会更新。 Contact
对象后,不会更新父引用。 我不明白我的错误在哪里。
package test;
import java.util.ArrayList;
import java.util.List;
import javax.jdo.PersistenceManager;
import javax.jdo.PersistenceManagerFactory;
import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.IdentityType;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;
import org.junit.Assert;
import org.junit.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import com.google.appengine.api.datastore.Key;
public class DatastoreJdoTest extends LocalServiceTestCase {
@Autowired
@Qualifier("persistenceManagerFactory")
PersistenceManagerFactory pmf;
@Test
public void testBatchInsert() {
Key contactKey;
PersistenceManager pm = pmf.getPersistenceManager();
try {
pm.currentTransaction().begin();
User user = new User();
Contact contact = new Contact("contact1");
user.contacts.add(contact);
/*
* With this an exception is thrown
*
* Detected attempt to establish User(1)/Contact(2) as the parent of
* User(1) but the entity identified by User(1) has already been
* persisted without a parent. A parent cannot be established or
* changed once an object has been persisted.
* org.datanucleus.store.appengine.FatalNucleusUserException:
* Detected attempt to establish User(1)/Contact(2) as the parent of
* User(1) but the entity identified by User(1) has already been
* persisted without a parent. A parent cannot be established or
* changed once an object has been persisted. at
* org.datanucleus.store
* .appengine.DatastoreRelationFieldManager.checkForParentSwitch
* (DatastoreRelationFieldManager.java:204)
*/
//contact.user = user;
Assert.assertNull(contact.key);
pm.makePersistent(user);
Assert.assertNotNull(contact.key);
pm.currentTransaction().commit();
contactKey = contact.key;
//this assertion is broken. why ?
//Assert.assertNotNull(contact.user);
} finally {
if (pm.currentTransaction().isActive()) {
pm.currentTransaction().rollback();
}
}
Contact contact2 = pm.getObjectById(Contact.class, contactKey);
Assert.assertNotNull(contact2);
//this assertion is broken. why the contact don't store the parent user ?
Assert.assertNotNull(contact2.user);
}
}
@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
class User {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
public Key key;
@Persistent
public String name;
@Persistent
public List<Contact> contacts = new ArrayList<Contact>();
}
@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
class Contact {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
Key key;
@Persistent
public String contact;
@Persistent(mappedBy = "contacts", dependent = "true")
public User user;
public Contact(String contact) {
this.contact = contact;
}
}
根据App Engine文档 ,您应该在关系的所有者中指定“mappedBy”。
您可能还想阅读Max Ross的文章或查看我的代码 ,该代码从查询中获取的子对象(Message)访问父(Discussion)
只需发布带有修正的代码,Dmitry指出更容易阅读:
import java.util.ArrayList;
import java.util.List;
import javax.jdo.PersistenceManager;
import javax.jdo.PersistenceManagerFactory;
import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.IdentityType;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;
import org.junit.Assert;
import org.junit.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import com.google.appengine.api.datastore.Key;
public class DatastoreJdoTest extends LocalServiceTestCase {
@Autowired
@Qualifier("persistenceManagerFactory")
PersistenceManagerFactory pmf;
@Test
public void testBatchInsert() {
Key contactKey;
PersistenceManager pm = pmf.getPersistenceManager();
try {
pm.currentTransaction().begin();
User user = new User();
Contact contact = new Contact("contact1");
user.contacts.add(contact);
/*
* With this an exception is thrown
*
* Detected attempt to establish User(1)/Contact(2) as the parent of
* User(1) but the entity identified by User(1) has already been
* persisted without a parent. A parent cannot be established or
* changed once an object has been persisted.
* org.datanucleus.store.appengine.FatalNucleusUserException:
* Detected attempt to establish User(1)/Contact(2) as the parent of
* User(1) but the entity identified by User(1) has already been
* persisted without a parent. A parent cannot be established or
* changed once an object has been persisted. at
* org.datanucleus.store
* .appengine.DatastoreRelationFieldManager.checkForParentSwitch
* (DatastoreRelationFieldManager.java:204)
*/
//contact.user = user;
Assert.assertNull(contact.key);
pm.makePersistent(user);
Assert.assertNotNull(contact.key);
pm.currentTransaction().commit();
contactKey = contact.key;
//this assertion is broken. why ?
//Assert.assertNotNull(contact.user);
} finally {
if (pm.currentTransaction().isActive()) {
pm.currentTransaction().rollback();
}
}
Contact contact2 = pm.getObjectById(Contact.class, contactKey);
Assert.assertNotNull(contact2);
//this assertion is broken. why the contact don't store the parent user ?
Assert.assertNotNull(contact2.user);
}
}
@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
class User {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
public Key key;
@Persistent
public String name;
@Persistent(mappedBy = "user", dependent = "true")
public List<Contact> contacts = new ArrayList<Contact>();
}
@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
class Contact {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
Key key;
@Persistent
public String contact;
@Persistent
public User user;
public Contact(String contact) {
this.contact = contact;
}
}
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