使用游标对象化分页 [英] Objectify paging with Cursors
问题描述
我在我的RPC服务中有这个方法:
I have this method in my RPC service:
@Override
public Entrata[] getEntrate(int from, int to) {
List<Entrata> data = entrateDao.list();
return data.toArray(new Entrata[0]);
}
正如你所看到的,我不使用这两个参数,一个SQL世界,我将使用LIMIT和OFFSET。
As you can see, I am not using the two parameters, which, in a SQL world, I would use as LIMIT and OFFSET.
现在还不清楚我要做什么,我开始阅读:
http://code.google.com/p/objectify-appengine/wiki/IntroductionToObjectify#Cursors
It's not completely clear what I have to do now, I started reading this: http://code.google.com/p/objectify-appengine/wiki/IntroductionToObjectify#Cursors
我想我必须做一个query.startCursor()
I think I have to do a query.startCursor()
然后迭代TO页面大小。
Then iterate for "TO" times, the page size.
好吧?你能帮我一些片段吗? :)
All right? Can you help me with some snippets? :)
推荐答案
游标让您在查询结果集中使用检查点,存储检查点
From docs: Cursors let you take a "checkpoint" in a query result set, store the checkpoint elsewhere, and then resume from where you left off late
由于您只需要限制/抵消,您必须使用 limit )
和 offset()
的方法。喜欢:
As you need just limit/offset, you have to use limit()
and offset()
method of Objectify Query. Like:
ob.query(Entrata.class).limit(to - from).offset(from)
或者,当您有游标时:
String cursor = // get it from request
Query<Entrata> query = ob.query(Entrata.class);
Query q = query.startCursor(Cursor.fromWebSafeString(cursor));
q.limit(x);
QueryResultIterator<Entrate> iterator = query.iterator()
List<Entrate> data = // fetch data
String newCursor = iterrator.getStartCursor().toWebSafeString()
return new EntrataListWithCursor(data, cursor);
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