Mybatis 联合查询XML与注解对比

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;
}
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UserInfo.java

@Alias("UserInfo")
public class UserInfo {
    private Integer id;
    private User user;
    private String name;
}
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UserMessage.java

@Alias("UserMessage")
public class UserMessage {
    private Integer userId;
    private UserInfo userInfo;
    private List<Message> messages;
}
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Message.java

@Alias("Message")
public class Message {
    private Integer id;
    private Integer userId;
    private String content;
    private Timestamp time;
}
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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>
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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;
}
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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
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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]]]]
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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
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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;
}
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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
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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]]]]
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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
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