Jdo坚持一对多拥有双向导航的关系

Jdo坚持一对多拥有双向导航的关系

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Gae Jdo坚持一对多拥有双向导航的关系

本文介绍了Gae Jdo坚持一对多拥有双向导航的关系的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述



我手动将添加到到 User class，我期望最后 Contact 将会有对父节点 User 对象的引用。




  • 如果我在坚持父对象之前手动配置它，我会得到一个
    异常： org。 datanucleus.store.appengine.DatastoreRelationFieldManager.checkForParentSwitch（DatastoreRelationFieldManager.java:204）

  • 在 User 对象持久性父引用不是
    更新。

  • 使用密钥从
    数据存储中检索 Contact 对象后，父引用不会更新。
    • >


我不明白我的错误所在。 

 包测试; 
 
 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 keyKey; 
 PersistenceManager pm = pmf.getPersistenceManager（）; 
 try {
 pm.currentTransaction（）。begin（）; 
 User user = new User（）; 
联系人联系人=新联系人（contact1）; 
 user.contacts.add（contact）; 
 $ b $ * * 
 *由此抛出异常
 * 
 *检测到建立User（1）/ Contact（2）作为$ b的父项的尝试$ b *用户（1），但由用户（1）标识的实体已经被
 *持久化，没有父母。一旦对象被保存，父代不能建立或者
 *改变。 
 * org.datanucleus.store.appengine.FatalNucleusUserException：
 *检测到建立User（1）/ Contact（2）作为
 * User（1）的父项的尝试，但确定的实体由用户（1）已经被
 *坚持没有父母。一旦对象被保存，父代不能建立或者
 *改变。 at 
 * org.datanucleus.store 
 * .appengine.DatastoreRelationFieldManager.checkForParentSwitch 
 *（DatastoreRelationFieldManager.java:204）
 * / 
 //contact.user =用户; 
 Assert.assertNull（contact.key）; 
 pm.makePersistent（user）; 
 Assert.assertNotNull（contact.key）; 
 
 pm.currentTransaction（）。commit（）; 
 
 contactKey = contact.key; 
 //这个断言被破坏了。为什么？ 
 //Assert.assertNotNull (contact.user）; 
} finally {
 if（pm.currentTransaction（）。isActive（））{
 pm.currentTransaction（）。rollback（）; 
} 
} 
联系contact2 = pm.getObjectById（Contact.class，contactKey）; 
 Assert.assertNotNull（contact2）; 
 //这个断言被破坏了。为什么联系人不存储父母用户？ 
 Assert.assertNotNull（contact2.user）; 
 
 
 
 @PersistenceCapable（identityType = IdentityType.APPLICATION，detachable =true）
 class User {
 @PrimaryKey 
 @Persistent（valueStrategy = IdGeneratorStrategy.IDENTITY）
公钥键; 
 @Persistent 
公共字符串名称; 
 @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用户用户; 
 
 public Contact（String contact）{
 this.contact = contact; 
 
 
 
 $ div $解析方案

要，您应指定mappedBy您的关系的所有者。



您可能还想阅读或查看从子对象（消息）访问父（讨论）它是从查询中获取的

I'm trying to persist a one-to-many owned relationship with bidirectional navigation in GAE using JDO.

I manually add the Contact to User class, and I would expect that in the end the Contact will have a reference to the parent User object.

  • If I configure this manually before I persist the parent, I get an exception: org.datanucleus.store.appengine.DatastoreRelationFieldManager.checkForParentSwitch(DatastoreRelationFieldManager.java:204)
  • After the User object persistence the parent reference is not updated.
  • After the Contact object is retrieved from the datastore using the key the parent reference is not updated.

I don't understand where my mistake is.

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;
    }
}
解决方案

According to App Engine docs, you should specify "mappedBy" in the owner of your relationship.

You may also want to read Max Ross's article or to have a look at my code which accesses parent (Discussion) from a child object (Message) which is fetched from a query

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09-05 01:17
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