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我有一个具有 ChildEntities ArrayList 的 TestEntity。他们加入了一个拥有的关系。我想从数据存储中获取实体，更新子实体中的 int 字段，然后交换两个子实体的位置。但是，一旦我交换实体，似乎对 int 字段的更新就被删除了。我是否不允许将 JDO 持久对象存储在临时变量中以进行交换？这是我的测试代码，后面是实体本身的定义。当我在调试器中单步执行代码时，只要我将第二个值复制到列表中的位置 0，我的 ChildEntity 就会被覆盖或重置或其他任何东西。恐怕我缺少一些关于 JDO 工作原理的东西。

@Test
public void testSwap() {
    PersistenceManager pm = PMF.get().getPersistenceManager();

    TestEntity te = new TestEntity();
    pm.makePersistent(te);
    te.getChildEntities().add(new TestChildEntity("a"));
    te.getChildEntities().add(new TestChildEntity("b"));
    long id = te.getId();
    pm.close();
    pm = PMF.get().getPersistenceManager();
    te = pm.getObjectById(TestEntity.class, id);

    List<TestChildEntity> children = te.getChildEntities();
    for (TestChildEntity tce : children) {
        tce.setFoo(3);
    }

    TestChildEntity temp = children.get(0);
    children.set(0, children.get(1));   

        // after the above line executes, the object referred to by temp is overwritten/reset when i watch in debugger.

    children.set(1, temp);
    assertEquals(3, children.get(0).getFoo());  // these asserts will both fail.
    assertEquals(3, children.get(1).getFoo());

}

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class TestEntity {
        @PrimaryKey
        @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
        private Long id;

        @Persistent(mappedBy = "parent")
        private List<TestChildEntity> childEntities;

        public List<TestChildEntity> getChildEntities() {
                return childEntities;
        }

        public Long getId() {
                return id;
        }

        public static void demonstrateProblemWithRemove() {
                PersistenceManager pm = PMF.get().getPersistenceManager();
                TestEntity te = new TestEntity();
                pm.makePersistent(te);
                te.getChildEntities().add(new TestChildEntity("a"));
                te.getChildEntities().remove(0);
                pm.close();
        }

}

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class TestChildEntity {
        @PrimaryKey
        @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
        @Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value
= "true")
        private String encodedKey;

        @Persistent
        @Extension(vendorName = "datanucleus", key = "gae.pk-name", value =
"true")
        private String keyName;

        @Persistent
        private int foo;

        @Persistent
        private TestEntity parent;

        public TestChildEntity(String k) {
                this.keyName = k;
                this.foo = 1;
        }

        public int getFoo() {
                return foo;
        }

        public void setFoo(int foo) {
                this.foo = foo;
        }
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1 回答 1

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Try adding defaultFetchGroup = "true" to @Persistent annotation above TestEntity.childEntities

By default, childEntities aren't fetched from datastore (it is JDO behavior, as far as I know, nothing specific to AppEngine). In your case, I suppose, they are even not written because you call makePersistent before you add children.

于 2009-11-17T22:16:46.633 回答