如何使用祖先（）正确存储和查询 Objectify 实体？ [关闭]

Question

存储和查询 Objectify 实体的正确方法是什么，该实体涉及标有 Objectify 的 @Parent 注释的字段？请提供使用ancestor() 查询的示例。

Answer 1

有几个要求：

1. 索引 - 确保查询的字段已编入索引

2. 祖先 - 确保使用ancestor(parent)

3. 提交 - 确保已提交保存

4. 附件 - 确保将子项附加到父项并保存

5. 验证 id 是否匹配，而不是 Java 对象实例 - 当您读回它时，它将是一个不同的 Java 对象。但是标有Objectify的@Id的字段应该是一样的

6. 使用 .now() 保存并使用 .now() 回读 - 请参阅 Why .now()? (Objectify) 和 Objectify error "You cannot create a Key for an object with a null @Id" in JUnit

7. 不要尝试将标记为@Parent 的字段用作您要过滤的字段；改为复制该字段

8. datastore-indexes.xml - 如果您要查询实体并过滤多个字段，那么 Objectify 的 @Index 注释是不够的。您还必须在[datastore-indexes.xml](https://cloud.google.com/appengine/docs/java/config/indexconfig) 中输入一个条目。感谢 Patrice 在 cmets 中提到这一点。

这是我正在编写的一些代码的草图，我让它在单元测试中工作。

RepositoryTest

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.equalTo;
import com.googlecode.objectify.ObjectifyService;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

public class RepositoryTest {
    // Tests under worst case of replication https://stackoverflow.com/questions/27727338/which-is-better-setdefaulthighrepjobpolicyunappliedjobpercentage100-vs-custo
    private final LocalServiceTestHelper helper =
            new LocalServiceTestHelper(new LocalDatastoreServiceTestConfig()
                .setDefaultHighRepJobPolicyUnappliedJobPercentage(100)); 

    private Closeable closeable;
    private Repository repository;

    @Before
    public void setup() {
        helper.setUp();
        repository = new Repository();
        ObjectifyService.register(MyCategory.class);
        ObjectifyService.register(MyItem.class);
        closeable = ObjectifyService.begin(); // https://stackoverflow.com/questions/27726961/how-to-resolve-you-have-not-started-an-objectify-context-in-junit
    }

    @After
    public void tearDown() {
        closeable.close();
        helper.tearDown();
    }

    @Test
    public void testLookupMyItemShouldSucceed() {
        MyCategory myCategory = repository.createMyCategory();

        int zero = 0;
        int one = 1;
        int two = 2;

        addMyItem(myCategory, zero, "a");
        MyItem expectedMyItem = addMyItem(myCategory, one, "b");
        addMyItem(myCategory, two, "c");

        MyItem actualMyItem = repository.lookupMyItem(myCategory, one);

        assertThat(actualMyItem, Matchers.notNullValue());
        assertThat(actualMyItem.id, equalTo(expectedMyItem.id));
    }

    private MyItem addMyItem(MyCategory myCategory, long index, String label) {
        MyItem myItem = repository.createMyItem();
        myItem.setParent(myCategory);
        myItem.setGroup(myCategory);
        myItem.index = index;
        myItem.label = label;
        repository.updateMyItem(myItem);
    }
}

存储库

import static com.googlecode.objectify.ObjectifyService.begin;
import static com.googlecode.objectify.ObjectifyService.ofy;
import com.googlecode.objectify.util.Closeable;

public class Repository {
    public Topic createMyCategory() {
        Topic entity = topicProvider.get();
        updateTopic(entity);
        return entity;
    }   

    public MyItem lookupMyItem(MyCategory myCategory, long i) {
        return ofy().load().type(MyItem.class).ancestor(myCategory).filter(MyItem.MyCategoryField, myCategory).filter(MyItem.IndexField, i).first().now();
    }
}

我的物品

import com.googlecode.objectify.Ref;
import com.googlecode.objectify.annotation.Entity;
import com.googlecode.objectify.annotation.Id;
import com.googlecode.objectify.annotation.Index;
import com.googlecode.objectify.annotation.Parent;

@Entity
public class MyItem {
    @Id public Long id;
    @Parent private Ref<MyCategory> parent;

    @Index private Ref<MyCategory> myCategory; public static final String MyCategoryField = "myCategory";   
    @Index public Long index; public static final String IndexField = "index"; 

    public String label;
    public long weight;

    public MyCategory getGroup() {
        return group.get();
    }

    public void setGroup(MyCategory group) {
        this.group = Ref.create(group);
    }

    public MyCategory getParent() {
        return parent.get();
    }

    public void setParent(MyCategory group) {
        this.parent = Ref.create(group);
    }
}

我的类别

import com.googlecode.objectify.annotation.Entity;
import com.googlecode.objectify.annotation.Id;

@Entity
public class MyCategory {
    @Id public Long id;
}

datastore-indexes.xml

<?xml version="1.0" encoding="utf-8"?>
<datastore-indexes autoGenerate="true">
    <datastore-index kind="MyItem" ancestor="true">
        <property name="myCategory" direction="asc" />
        <property name="index" direction="asc" />
    </datastore-index>
</datastore-indexes>

上面的代码中可能存在语法错误或拼写错误，因为为了清楚起见，我对原始代码进行了修改。单元测试确实通过并且始终通过（即它有时不会因为 eventual consistency 而失败）。