由于是练习，故只做了感兴趣的一部分测试。
测试类容
XML配置转注解方式
实体类
为了测试请忽略设计是否合理…
User.java
@Alias("User")
public class User {
private Integer id;
private String username;
private String password;
private Timestamp birthday;
private Boolean sex;
}
1
2
3
4
5
6
7
8
UserInfo.java
@Alias("UserInfo")
public class UserInfo {
private Integer id;
private User user;
private String name;
}
1
2
3
4
5
6
UserMessage.java
@Alias("UserMessage")
public class UserMessage {
private Integer userId;
private UserInfo userInfo;
private List<Message> messages;
}
1
2
3
4
5
6
Message.java
@Alias("Message")
public class Message {
private Integer id;
private Integer userId;
private String content;
private Timestamp time;
}
1
2
3
4
5
6
7
三表之间的关联为 userId
XML配置方式
XML配置
<select id="selectUserInfoAndMessages" resultMap="UserMessages">
select
ui.id as uiid,
ui.name as name,
ui.user_id as info_user_id,
u.id as user_id,
u.username
as username,
u.password as password,
u.birthday as birthday,
u.sex as
sex,
um.id as umid,
um.user_id as um_user_id,
um.content as content,
um.time as um_time
from user_info ui
left outer join user u on u.id = ui.user_id
left outer join user_message um
on u.id = um.user_id
where u.id = #{id}
</select>
<resultMap type="UserMessage" id="UserMessages">
<id property="userId" column="user_id" />
<association property="userInfo" column="info_user_id"
javaType="UserInfo">
<id property="id" column="uiid" />
<result property="name" column="name" />
<association property="user" column="user_id" javaType="User">
<id property="id" column="user_id" />
<result property="username" column="username" />
<result property="password" column="password" />
<result property="birthday" column="birthday" />
<result property="sex" column="sex" />
</association>
</association>
<collection property="messages" javaType="ArrayList"
ofType="Message">
<id property="id" column="umid" />
<result property="userId" column="user_id" />
<result property="content" column="content" />
<result property="time" column="um_time" />
</collection>
</resultMap>
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
查询方法
public List<UserMessage> testSelectUserInfoAndMessages(Integer userId) {
try (SqlSession session = sessionFactory.openSession()) {
//映射器方式调用
//return session.getMapper(UserMapper.class).selectUserInfoAndMessage(userId);
return session.selectList("mybatis.dao.mappers.UserMapper.selectUserInfoAndMessages", userId);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
1
2
3
4
5
6
7
8
9
10
执行过程
==> Preparing: select ui.id as uiid, ui.name as name, ui.user_id as info_user_id, u.id as user_id, u.username as username, u.password as password, u.birthday as birthday, u.sex as sex, um.id as umid, um.user_id as um_user_id, um.content as content, um.time as um_time from user_info ui left outer join user u on u.id = ui.user_id left outer join user_message um on u.id = um.user_id where u.id = ?
==> Parameters: 9(Integer)
<== Columns: uiid, name, info_user_id, user_id, username, password, birthday, sex, umid, um_user_id, content, um_time
<== Row: 5, 江流, 9, 9, test中文2, 1234567, 2018-07-17 17:04:09.0, 0, 1, 9, 信息1, 2018-07-18 11:36:58.0
<== Row: 5, 江流, 9, 9, test中文2, 1234567, 2018-07-17 17:04:09.0, 0, 2, 9, 信息2, 2018-07-18 11:37:05.0
<== Total: 2
1
2
3
4
5
6
结果
[UserMessage [userId=9, userInfo=UserInfo [id=5, user=User [id=9, username=test中文2, password=1234567, birthday=2018-07-17 17:04:09.0, sex=false], name=江流], messages=[Message [id=1, userId=9, content=信息1, time=2018-07-18 11:36:58.0], Message [id=2, userId=9, content=信息2, time=2018-07-18 11:37:05.0]]]]
1
此种方式只查询了一次，结果集被过滤了重复项目，最终集合中只有一个UserMessage对象。
注解方式
注解方法
@Select("select * from user where id = #{userId}")
@Results(value = {
@Result(property="userId" , column="id"),
@Result(property="userInfo" , column="id", one = @One(select="mybatis.dao.mappers.UserMapper.getUserInfoByAnnotation")),
@Result(property="messages" , column = "id" , many= @Many(select="mybatis.dao.mappers.UserMapper.getUserMessagesByAnnotation"))
})
public List<UserMessage> selectUserInfoAndMessagesByAnnotation(Integer userId);//查询用户信息和用户消息
@Select("select * from user_info where user_id = #{userId}")
@Results(value={
@Result(property="id" , column="id"),
@Result(property="name" , column = "name"),
@Result(property="user" , column = "user_id" , one = @One(select="mybatis.dao.mappers.UserMapper.getUserByAnnotation"))
})
public UserInfo getUserInfoByAnnotation(Integer userId);//查询用户信息
@Select("select * from user where id = #{userId}")
public User getUserByAnnotation(Integer userId);//查询用户
@Select("select * from user_message where user_id = #{userId}")
public List<Message> getUserMessagesByAnnotation(Integer userId);//查询用户消息集合
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
查询方法
public List<UserMessage> testSelectUserMessagesByAnnotation(Integer userId) {
try (SqlSession session = sessionFactory.openSession()) {
return session.getMapper(UserMapper.class).selectUserInfoAndMessagesByAnnotation(userId);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
1
2
3
4
5
6
7
8
执行过程
==> Preparing: select * from user where id = ?
==> Parameters: 9(Integer)
<== Columns: id, username, password, sex, birthday
<== Row: 9, test中文2, 1234567, 0, 2018-07-17 17:04:09.0
====> Preparing: select * from user_info where user_id = ?
====> Parameters: 9(Integer)
<==== Columns: id, user_id, name
<==== Row: 5, 9, 江流
======> Preparing: select * from user where id = ?
======> Parameters: 9(Integer)
<====== Columns: id, username, password, sex, birthday
<====== Row: 9, test中文2, 1234567, 0, 2018-07-17 17:04:09.0
<====== Total: 1
<==== Total: 1
====> Preparing: select * from user_message where user_id = ?
====> Parameters: 9(Integer)
<==== Columns: id, user_id, content, time
<==== Row: 1, 9, 信息1, 2018-07-18 11:36:58.0
<==== Row: 2, 9, 信息2, 2018-07-18 11:37:05.0
<==== Total: 2
<== Total: 1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
可以看出执行了几次查询语句。
结果
[UserMessage [userId=9, userInfo=UserInfo [id=5, user=User [id=9, username=test中文2, password=1234567, birthday=2018-07-17 17:04:09.0, sex=false], name=江流], messages=[Message [id=1, userId=9, content=信息1, time=2018-07-18 11:36:58.0], Message [id=2, userId=9, content=信息2, time=2018-07-18 11:37:05.0]]]]
1
总结
XML执行联合查询效率是要高一些的
注解方式方法倒是可以独立使用，虽然XML也可以用select属性
混合使用更好
套用官方的话
1
因为最初设计时，MyBatis 是一个 XML 驱动的框架。配置信息是基于 XML 的，而且映射语句也是定义在 XML 中的。而到了 MyBatis 3，就有新选择了。MyBatis 3 构建在全面且强大的基于 Java 语言的配置 API 之上。这个配置 API 是基于 XML 的 MyBatis 配置的基础，也是新的基于注解配置的基础。注解提供了一种简单的方式来实现简单映射语句，而不会引入大量的开销。
2
注意 不幸的是，Java 注解的的表达力和灵活性十分有限。尽管很多时间都花在调查、设计和试验上，最强大的 MyBatis 映射并不能用注解来构建——并不是在开玩笑，的确是这样。比方说，C#属性就没有这些限制，因此 MyBatis.NET 将会比 XML 有更丰富的选择。也就是说，基于 Java 注解的配置离不开它的特性。
END
附 数据表SQL
CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(25) DEFAULT NULL,
`password` varchar(25) DEFAULT NULL,
`sex` bit(1) DEFAULT b'1',
`birthday` datetime DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=16 DEFAULT CHARSET=utf8;
CREATE TABLE `user_info` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`user_id` int(11) DEFAULT NULL,
`name` varchar(25) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `user_id` (`user_id`),
CONSTRAINT `user_info_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
CREATE TABLE `user_message` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`user_id` int(11) DEFAULT NULL,
`content` varchar(255) DEFAULT NULL,
`time` datetime DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `message_ibfk_1` (`user_id`),
CONSTRAINT `user_message_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
---------------------
作者：很倔也很天真
来源：CSDN
原文：https://blog.csdn.net/wang845252276/article/details/81120504
版权声明：本文为博主原创文章，转载请附上博文链接！