子数据存储实体的键返回为 null

Question

我有一个典型的 Person-Address 实体关系。在查询数据存储中的 Person 之后，我会查询 Person 以获取地址键。密钥（即addrKey，见下文）始终返回为空。但是我查看数据存储区，我看到了 Person 和 Address 实体，以及它们的键。很明显，Key addrKey = (Key) person.getProperty("address") 这条线并没有做我认为应该做的事情。任何想法如何解决这个问题？

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");
…
}

Answer 1

我的猜测是您同时保留了地址和人员。但是，默认情况下，地址在持久化之前具有不完整的键（假设您依赖于键的自动 id 生成）。因此，您亲自存储了不完整的密钥。并且使用不完整的键获取将不起作用。

我写了一个快速测试用例：

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);
    }
  }

}

这是输出：

<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.

如果我错了，很高兴能理解为什么你的示例中有一个 try catch。在 pre-put 时间和 pos-get 时间打印出 Person 实体和 Address 实体也很好。