java - 事务中的祖先查询(objectify)返回数据 "frozen in time"

Question

直接举例:

@Entity
public class Parentt {
    @Id
    String id;
}

@Entity
public class Child {
    @Parent 
    Ref<Parentt> parenttRef;
    @Id
    String id;
}

public void test() {
final Parentt parentt = new Parentt();
        ofy().transact(new VoidWork() {
            @Override
            public void vrun() {

                parentt.setId(UUID.randomUUID().toString());
                ofy().save().entity(parentt).now();
                Child child = new Child();
                child.setId(UUID.randomUUID().toString());
                child.setParentt(parentt.getId());
                ofy().save().entity(child).now();

                LOG.info("query result size: " + ofy().load().type(Child.class).ancestor(parentt).list().size());
                ofy().flush();
                LOG.info("query result size: " + ofy().load().type(Child.class).ancestor(parentt).list().size());

            }
        });

        LOG.info("query result size(outside of transaction): " + ofy().load().type(Child.class).ancestor(parentt).list().size());
}

test()方法内的代码生成的结果:

query result size: 0

query result size: 0

query result size(outside of transaction): 1

我在 Objectify 文档中找到了:

There are some quirks at the low-level API: For example, get()s and query()s will see the datastore "frozen in time" and will not reflect updates even within the transaction. Objectify hides this behavior from you; subsequent fetches will see the same data seen (or updated) previously. Note that since queries are always run inside of GAE, indexes (ie, filtering operations) always appear to be frozen in time - Objectify can't hide this.

祖先查询是否基于内部索引，这就是查询在事务内部不返回结果的原因(这里除了父级之外没有其他过滤)？

Answer 1

查询本质上是基于索引的 - 它们通过到 GAE 的往返来提供服务。因此 GAE 的行为定义了返回值。 Objectify 在这里确实无能为力。