[英]Gae Jdo persistance on one-to-many owned relationship with bidirectional navigation
[英]JDO GAE One-to-Many problem
嗨,我在从数据存储中检索数据时遇到了一些问题...
我有一些马戏团,有一定的吸引力。
马戏团:
@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class Circus implements Serializable
{
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
@Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value = "true")
private String key;
@Persistent
private String name;
@Persistent(mappedBy = "owningCircus")
@Element(dependent = "true")
public List<Attractions> attractions;
public Circus()
{
}
public Circus(String name)
{
this.name = name;
this.attractions = new ArrayList<Attractions>();
}
public void addAttraction(Attraction attr)
{
this.attractions.add(attr);
}
// Get/Set
}
景点:
@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class Attraction implements Serializable
{
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
@Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value = "true")
private String key;
@Persistent
private String name;
@Persistent
private Circus owningCircus;
//...
public Attraction()
{
}
public Attraction(Circus owning, String name)
{
this.name = name;
this.owningCircus = owning;
}
// Get/Set
}
这就是我得到马戏团的方式
public List<Circus> getCircuses()
{
PersistenceManager pm = PMF.get().getPersistenceManager();
Query query = pm.newQuery("select from " + Circus.class.getName());
List<Circus> circuses = (List<Circus>) query.execute();
for(Circus c : circuses)
{
//Poke the list of attractions so they are loaded.
//however, c.attractions==null => NullPointerException
c.attractions.size();
}
List<Circus> ret = (List<Circus>) pm.detachCopyAll(circuses);
pm.close();
return ret;
}
马戏团像这样坚持
public void addCircus(Circus circus)
{
PersistenceManager pm = PMF.get().getPersistenceManager();
pm.makePersistent(circus);
pm.close();
}
//...
Circus a =new Circus("Super Circus");
a.addAttraction(new Attraction(a,"George the clown"));
addCircus(a);
c.attractions由于某种原因为空。.如果我查看数据查看器,则有马戏团和景点。.:s
谢谢
编辑:添加了如何保留马戏团,以及owningCircus。
编辑2
我实际上正在收到此异常:
com.google.appengine.api.datastore.DatastoreNeedIndexException: no matching index found.. <datastore-index kind="Attraction" ancestor="true" source="manual">
<property name="attractions_INTEGER_IDX" direction="asc"/>
添加包含的datastore-indexes.xml
<?xml version="1.0" encoding="utf-8"?> <datastore-indexes autoGenerate="true">
<datastore-index kind="Attraction" ancestor="true" source="manual">
<property name="attractions_INTEGER_IDX" direction="asc"/>
</datastore-index>
</datastore-indexes>
war / WEB-INF /解决了这个问题。
在GAE上的JDO中,类型化引用表示拥有关系。 因此,要使其正常工作,请尝试添加
@Persistent(mappedBy="owningCircus")
马戏团和吸引力添加字段
@Persistent private Circus owningCircus;
这样,在创建新景点时,设置马戏团将隐式映射关系。 (请参阅下面的链接中的“实体组”)
如果您不希望拥有自己的关系,只需持有钥匙清单即可。 有关更多信息,请访问http://code.google.com/appengine/docs/java/datastore/jdo/relationships.html
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