使用Java在Google App Engine中进行分页 [英] Pagination in Google App Engine with Java

问题描述

我需要创建简单的对象分页，但是当我阅读手册时，我发现query.setRange（5，10）;将获取10个对象，即使只需要5个对象。

有没有办法获取刚才需要的对象？

<编辑：我开始赏金，所以你可以告诉我简单的示例代码在Java中的作品，然后我会接受你的答案。

这个如何：

  List< Employee> results =（List< Employee>）query.execute（）; 
 //使用前20个结果... 
 
 Cursor cursor = JPACursorHelper.getCursor（results）; 
字符串cursorString = cursor.toWebSafeString（）; 
 //存储cursorString ... 
 
 // ... 
 
 //查询查询=产生光标的相同查询
 / / String cursorString =存储的字符串
 Cursor cursor = Cursor.fromWebSafeString（cursorString）; 
 query.setHint（JPACursorHelper.CURSOR_HINT，cursor）; 
 query.setRange（0，20）; 
 
列表<员工> results =（List< Employee>）query.execute（）; 
 //使用下面的20个结果... 
  

发件人：

如何使用数据存储在GAE上使用jpa游标

另外：

http://groups.google.com/group/google-appengine-java/browse_thread/thread / 5223215ff24c3b3e / d22297d1d76a9c8b

或者没有JPA请参阅：

http://code.google.com/appengine/docs /java/javadoc/com/google/appengine/api/datastore/Cursor.html

I need to create simple pagination of objects, but when I read manual I found out that query.setRange(5, 10); will fetch 10 objects, even when only 5 objects are needed.

Is there anyway to fetch just needed objects?

EDIT: I started bounty, so fi you can show me simple example code in Java that works, then I will accept you answer.

解决方案

How about this:

List<Employee> results = (List<Employee>) query.execute();
// Use the first 20 results...

Cursor cursor = JPACursorHelper.getCursor(results);
String cursorString = cursor.toWebSafeString();
// Store the cursorString...

// ...

// Query query = the same query that produced the cursor
// String cursorString = the string from storage
Cursor cursor = Cursor.fromWebSafeString(cursorString);
query.setHint(JPACursorHelper.CURSOR_HINT, cursor);
query.setRange(0, 20);

List<Employee> results = (List<Employee>) query.execute();
// Use the next 20 results...

From:

How to use datastore cursors with jpa on GAE

Also:

http://groups.google.com/group/google-appengine-java/browse_thread/thread/5223215ff24c3b3e/d22297d1d76a9c8b

Or without JPA see:

http://code.google.com/appengine/docs/java/javadoc/com/google/appengine/api/datastore/Cursor.html

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