插件发布到市场后，后续版本迭代的过程中，可能会对ao实体类的字段作添加或删除，或者要将某一字段的值映射解析到另一字段上。
本来这个工作，可以在插件启动的时候，在实现了com.atlassian.sal.api.lifecycle.LifecycleAware 接口的类onStart方法类完成。
但是历史版本更新了哪些字段不好维护，以前查看其它插件的代码时有看到版本更新任务的代码，但是因为实际工作中用的很少，就没去细看。
这几天查看atlassian的文档时，发现有一篇专门介绍如何处理upgradTask的文档。其实这篇文档是在一个系列中的，话说回来，atlassian插件开发的文档虽然挺全的，但是总体的文档结构还是有点乱的。
官网链接：处理AO升级任务
下文是对文档上的一些内容的截取
比如说我们之前有一个Todo类，它继承了Entity
1 @Preload
2 public interface Todo extend Entity {
3 void setUserName （String userName ）;
4
5 String getUserName （）;
6
7 String getDescription （）;
8
9 void setDescription （String description ）;
10
11 boolean isComplete （）;
12
13 void setComplete （boolean complete ）;
14 }
Todo类中维护了一个userName字段，但是在后续的开发中，用户需要维护的信息很多，不止是用户名这么简单了。此时我们需要重新建一个User表，用来存放用户信息。
1 public interface User extends Entity
2 {
3 String getName();
4 void setName(String name);
5 }
Todo类也得做修改
1 package com.atlassian.tutorial.ao.todo;
2
3 import net.java.ao.Entity;
4 import net.java.ao.Preload;
5 import net.java.ao.schema.NotNull;
6
7 @Preload
8 public interface Todo extends Entity
9 {
10 @NotNull
11 void setUser(User user);
12
13 @NotNull
14 User getUser();
15
16 String getDescription();
17
18 void setDescription(String description);
19
20 boolean isComplete();
21
22 void setComplete(boolean complete);
23 }
24
之前service里的方法当然得修改，但这不是我们这里讨论的重点，接下来我们看，如何使用upgradetask更新数据库数据。
首先在ao包下面新建一个pacakge，名为upgrade.v2(官网上还建了v1包，但是那个升级改动较小，这里就不详述了)。
每次版本更新都要新建一个（v版本号）的包，包内存放需要更新的数据库实体类(从ao.entity包内复制过来，并做相应的改动。它不会在数据库内重新建一张表，只是用来记录更新信息)和更新任务类
1 package com.atlassian.tutorial.ao.todo.upgrade.v2;
2
3 import net.java.ao.Entity;
4 import net.java.ao.Preload;
5 // 保留了需要更新掉的字段user_name和需要新增的user_id字段（即getUser）
6 @Preload
7 public interface Todo extends Entity
8 {
9 void setUserName(String userName);
10
11 String getUserName();
12
13 void setUser(User user);
14
15 User getUser();
16
17 String getDescription();
18
19 void setDescription(String description);
20
21 boolean isComplete();
22
23 void setComplete(boolean complete);
24 }
user表是新增的，没有改动，直接复制过来
接下来就是更新的代码类了
1 package com.atlassian.tutorial.ao.todo.upgrade.v2; // (1) 引用upgrade.v2包下的类
2
3 import com.atlassian.activeobjects.external.ActiveObjects;
4 import com.atlassian.activeobjects.external.ActiveObjectsUpgradeTask;
5 import com.atlassian.activeobjects.external.ModelVersion;
6 import com.google.common.collect.ImmutableMap;
7 import net.java.ao.Query;
8
9 public final class TodoUpgradeTask002 implements ActiveObjectsUpgradeTask
10 {
11 @Override
12 public ModelVersion getModelVersion()
13 {
14 return ModelVersion.valueOf("2"); // (2) 版本设置为2
15 }
16
17 @Override
18 public void upgrade(ModelVersion currentVersion, ActiveObjects ao)
19 {
20 ao.migrate(Todo.class, User.class); // (3) 声明需要操作的类
21
22 Todo[] todos = ao.find(Todo.class); // (4) 实际升级，设置User对应的userName。
23 for (Todo todo : todos)
24 {
25 todo.setUser(getOrCreateUser(ao, todo.getUserName()));
26 todo.save();
27 }
28 }
29
30 private User getOrCreateUser(ActiveObjects ao, String userName)
31 {
32 User[] users = ao.find(User.class, Query.select().where("NAME = ?", userName));
33 if (users.length == 0) {
34 return createUser(ao, userName);
35 } else if (users.length == 1) {
36 return users[0];
37 } else {
38 throw new IllegalStateException("There shouldn't be 2 users with the same username! " + userName);
39 }
40 }
41
42 private User createUser(ActiveObjects ao, String userName)
43 {
44 return ao.create(User.class, ImmutableMap.<String, Object>of("NAME", userName));
45 }
46 }
最后，需要在atlassian-plugin.xml中配置
1 <ao key="ao-module"> 2 <description>The module configuring the Active Objects service used by this plugin</description> 3 <entity>com.atlassian.tutorial.ao.todo.Todo</entity> 4 <entity>com.atlassian.tutorial.ao.todo.User</entity> 5 <upgradeTask>com.atlassian.tutorial.ao.todo.upgrade.v1.TodoUpgradeTask001</upgradeTask> 6 <upgradeTask>com.atlassian.tutorial.ao.todo.upgrade.v2.TodoUpgradeTask002</upgradeTask> 7 </ao>
执行，下面是官网给出的执行日志，
1 [INFO] [talledLocalContainer] INFO - assian.activeobjects.internal.ActiveObjectUpgradeManagerImpl - Starting upgrade of data model, current version is 1 2 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - CREATE TABLE AO_3F7D93_USER ( 3 [INFO] [talledLocalContainer] ID INTEGER GENERATED BY DEFAULT AS IDENTITY (START WITH 1) NOT NULL, 4 [INFO] [talledLocalContainer] NAME VARCHAR(255), 5 [INFO] [talledLocalContainer] PRIMARY KEY(ID) 6 [INFO] [talledLocalContainer] ) 7 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - ALTER TABLE AO_3F7D93_TODO ADD COLUMN USER_ID INTEGER 8 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - ALTER TABLE AO_3F7D93_TODO ADD CONSTRAINT fk_ao_3f7d93_todo_user_id FOREIGN KEY (USER_ID) REFERENCES AO_3F7D93_USER(ID) 9 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - CREATE INDEX index_ao_3f7d93_todo_user_id ON AO_3F7D93_TODO(USER_ID) 10 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - SELECT * FROM AO_3F7D93_TODO 11 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - SELECT ID FROM AO_3F7D93_USER WHERE NAME = ? 12 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - INSERT INTO AO_3F7D93_USER (NAME) VALUES (?) 13 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - UPDATE AO_3F7D93_TODO SET USER_ID = ? WHERE ID = ? 14 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - SELECT ID FROM AO_3F7D93_USER WHERE NAME = ? 15 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - UPDATE AO_3F7D93_TODO SET USER_ID = ? WHERE ID = ? 16 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - SELECT ID FROM AO_3F7D93_USER WHERE NAME = ? 17 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - INSERT INTO AO_3F7D93_USER (NAME) VALUES (?) 18 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - UPDATE AO_3F7D93_TODO SET USER_ID = ? WHERE ID = ? 19 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - SELECT ID FROM AO_3F7D93_USER WHERE NAME = ? 20 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - UPDATE AO_3F7D93_TODO SET USER_ID = ? WHERE ID = ? 21 [INFO] [talledLocalContainer] INFO - assian.activeobjects.internal.ActiveObjectUpgradeManagerImpl - Finished upgrading, model is up to date at version 2 22 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - ALTER TABLE AO_3F7D93_TODO DROP COLUMN USER_NAME 23 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - ALTER TABLE AO_3F7D93_TODO DROP CONSTRAINT fk_ao_3f7d93_todo_user_id 24 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - ALTER TABLE AO_3F7D93_TODO ALTER COLUMN USER_ID INTEGER NOT NULL 25 [INFO] [talledLocalContainer] DEBUG - net.java.ao.sql - ALTER TABLE AO_3F7D93_TODO ADD CONSTRAINT fk_ao_3f7d93_todo_user_id FOREIGN KEY (USER_ID) REFERENCES AO_3F7D93_USER(ID)
最后几行可以看出，在完成升级任务之后，数据库的表结构也变了，user_name字段被移除