Mybatis联合查询XML与注解对比分析

@Alias("User")
public class User {
    private Integer id;
    private String username;
    private String password;
    private Timestamp birthday;
    private Boolean sex;
}

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

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

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

<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>

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;
}

@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

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;
}

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;