![](/img/trans.png)
[英]Querying immediately for saved entity returns null sometimes - datastore
[英]key of child datastore entity returns as null
我有一個典型的Person-Address實體關系。 在查詢數據存儲區中的Person后,然后查詢Person以獲取地址密鑰。 鍵(即addrKey
,請參見下文)始終返回為null。 但是我看一下數據存儲區,看到Person和Address實體,以及它們的鍵。 因此,很明顯, Key addrKey = (Key) person.getProperty("address")
行Key addrKey = (Key) person.getProperty("address")
並沒有執行我認為應該做的事情。 任何想法如何解決這一問題?
DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
Map<Key, Entity> entities = datastore.get(keys);
List<Person> result = new ArrayList<Person>();
Iterator<Entry<Key, Entity>> it = entities.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<Key, Entity> ent = it.next();
final Entity person = ent.getValue();
Key key = person.getKey();
name = (Long) person.getProperty("name");
Address address = getAddress(datastore, person);
...
}
private Address getAddress(DatastoreService datastore, Entity person) {
Key addrKey = (Key) person.getProperty("address");
try {
Entity d = datastore.get(addrKey);
String street = (String) d.getProperty("street");
…
}
我的猜測是您同時保留住地址和個人。 但是,默認情況下,地址在保留之前具有不完整的密鑰(假設您依賴密鑰的自動ID生成)。 因此,您親自存儲了一個不完整的密鑰。 並且使用不完整密鑰進行的提取將不起作用。
我寫了一個快速測試用例:
import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.Key;
public class TempTest extends PersistenceTestHelper {
@Test
public void testStackOverflow() throws Exception {
Entity address = new Entity("address", 1);
address.setProperty("street", "my street");
Entity person = new Entity("person", 1);
person.setProperty("addressKey", address.getKey());
System.out.println(person);
DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
datastore.put(person);
datastore.put(address);
Entity personFromDatastore = datastore.get(person.getKey());
Key addressKey = (Key) personFromDatastore.getProperty("addressKey");
Entity addressFromDatastore = datastore.get(addressKey);
System.out.println("fetched street: " + addressFromDatastore.getProperty("street"));
address = new Entity("address");
System.out.println("Address with incomplete key: " + address.getKey());
try {
addressFromDatastore = datastore.get(address.getKey());
} catch (IllegalArgumentException e) {
System.out.println(e);
}
}
}
這是輸出:
<Entity [person(1)]:
addressKey = address(1)
>
fetched street: my street
Address with incomplete key: address(no-id-yet)
java.lang.IllegalArgumentException: address(no-id-yet) is incomplete.
如果我錯了,那么很高興理解為什么您的示例中有一個try catch。 而且,在投入前和事后獲取時,Person實體和Address實體的打印輸出也會很好。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.