MyBatis高级查询 一对一映射

drop database if exists simple;
create database simple;

use simple;
drop table if exists sys_user;
create table sys_user
(
    id bigint not null auto_increment comment ‘用户ID‘,
    user_name varchar(50) comment ‘用户名‘,
    user_password varchar(50) comment ‘密码‘,
    user_email varchar(50) comment ‘邮箱‘,
    user_info text comment ‘简介‘,
    head_img blob comment ‘头像‘,
    create_time datetime comment ‘创建时间‘,
    primary key (id)
);
alter table sys_user comment ‘用户表‘;

drop table if exists sys_role;
create table sys_role(
    id bigint not null auto_increment comment ‘角色ID‘,
    role_name varchar(50) comment ‘角色名‘,
    enabled int comment ‘有效标志‘,
    create_by bigint comment ‘创建人‘,
    create_time datetime comment ‘创建时间‘,
    primary key (id)
);
alter table sys_role comment ‘角色表‘;

drop table if exists sys_privilege;
create table sys_privilege
(
    id bigint not null auto_increment comment ‘权限ID‘,
    privilege_name varchar(50) comment ‘权限名称‘,
    privilege_url varchar(50) comment ‘权限URL‘,
    primary key (id)
);
alter table sys_privilege comment ‘权限表‘;

drop table if exists sys_user_role;
create table sys_user_role
(
    user_id bigint comment ‘用户ID‘,
    role_id bigint comment ‘角色ID‘
);
alter table sys_user_role comment ‘用户角色关联表‘;

drop table if exists sys_role_privilege;
create table sys_role_privilege
(
    role_id bigint comment ‘用户ID‘,
    privilege_id bigint comment ‘角色ID‘
);
alter table sys_role_privilege comment ‘角色权限关联表‘;

假如1个用户只能有1种角色sys_user和sys_role是通过sys_user_role一对一关联；

1.使用自动映射处理一对一关系；优点：当一定会使用到嵌套结果时使用。

　　1.在SysUser.class model中增加SysRole的对象。

private SysRole role;

　　2.在查询的xml Mapper文件中对查询出的role属性写出对应的属性名称。

 <select id="selectUserAndById" resultType="test.model.SysUser">
          select
              u.id,
              u.user_name userName,
              u.user_password userPassword,
              u.user_email userEmail,
              u.create_time createTime,
              u.user_info userInfo,
              u.head_img  headImg,
              r.id "role.id",
              r.role_name "role.roleName",
              r.enabled "role.enabled",
              r.create_by "role.createBy",
              r.create_time "role.createTime"
              from sys_user u inner join sys_user_role ur on u.id=ur.user_id
              inner join sys_role r on ur.user_id=r.id where u.id=#{id}
  </select>

2.使用resultMap配置一对一映射

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="test.dao.SysUserMapper">
  <resultMap id="BaseResultMap" type="test.model.SysUser">
    <!--
      WARNING - @mbggenerated
      This element is automatically generated by MyBatis Generator, do not modify.
    -->
    <id column="id" jdbcType="BIGINT" property="id" />
    <result column="user_name" jdbcType="VARCHAR" property="userName" />
    <result column="user_password" jdbcType="VARCHAR" property="userPassword" />
    <result column="user_email" jdbcType="VARCHAR" property="userEmail" />
    <result column="create_time" jdbcType="TIMESTAMP" property="createTime" />
    <result column="user_info" jdbcType="LONGVARCHAR" property="userInfo" />
    <result column="head_img" jdbcType="LONGVARBINARY" property="headImg" />

  </resultMap>

  <resultMap type="test.model.SysUser" id="userRoleResultMap" extends="BaseResultMap">
      <!-- role相关属性 -->
    <result column="role_id" jdbcType="BIGINT" property="role.id" />
    <result column="role_name" jdbcType="VARCHAR" property="role.roleName" />
    <result column="enabled" jdbcType="INTEGER" property="role.enabled" />
    <result column="create_by" jdbcType="BIGINT" property="role.createBy" />
    <result column="role_create_time" jdbcType="TIMESTAMP" property="role.createTime" />
  </resultMap>
  <!-- 注意返回 resultMap="userRoleResultMap"-->
  <select id="selectUserAndById" resultMap="userRoleResultMap">
          select
              u.id,
              u.user_name userName,
              u.user_password userPassword,
              u.user_email userEmail,
              u.create_time createTime,
              u.user_info userInfo,
              u.head_img  headImg,
              r.id role_id,
              r.role_name role_name,
              r.enabled enabled,
              r.create_by create_by,
              r.create_time role_create_time
              from sys_user u inner join sys_user_role ur on u.id=ur.user_id
              inner join sys_role r on ur.user_id=r.id where u.id=#{id}
  </select>
</mapper>

3.使用resultMap的associaction标签配置一对一映射

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="test.dao.SysUserMapper">
  <resultMap id="BaseResultMap" type="test.model.SysUser">
    <!--
      WARNING - @mbggenerated
      This element is automatically generated by MyBatis Generator, do not modify.
    -->
    <id column="id" jdbcType="BIGINT" property="id" />
    <result column="user_name" jdbcType="VARCHAR" property="userName" />
    <result column="user_password" jdbcType="VARCHAR" property="userPassword" />
    <result column="user_email" jdbcType="VARCHAR" property="userEmail" />
    <result column="create_time" jdbcType="TIMESTAMP" property="createTime" />
    <result column="user_info" jdbcType="LONGVARCHAR" property="userInfo" />
    <result column="head_img" jdbcType="LONGVARBINARY" property="headImg" />

  </resultMap>

  <!-- 继承上面的UserResultMap -->
  <resultMap type="test.model.SysUser" id="userRoleResultMap" extends="BaseResultMap">
      <!-- role相关属性 -->
      <!-- 对应的ResultMap在test.dao.SysRoleMapper这个命名控件中-->
    <association property="role" columnPrefix="role_" resultMap="test.dao.SysRoleMapper.BaseResultMap"></association>
  </resultMap>

  <select id="selectUserAndById" resultMap="userRoleResultMap">
          select
              u.id,
              u.user_name userName,
              u.user_password userPassword,
              u.user_email userEmail,
              u.create_time createTime,
              u.user_info userInfo,
              u.head_img  headImg,
              r.id role_id,
              r.role_name role_role_name,
              r.enabled role_enabled,
              r.create_by role_create_by,
              r.create_time role_create_time
              from sys_user u inner join sys_user_role ur on u.id=ur.user_id
              inner join sys_role r on ur.user_id=r.id where u.id=#{id}
  </select>
<mapper/>

<mapper namespace="test.dao.SysRoleMapper">
  <resultMap id="BaseResultMap" type="test.model.SysRole">
    <!--
      WARNING - @mbggenerated
      This element is automatically generated by MyBatis Generator, do not modify.
    -->
    <id column="id" jdbcType="BIGINT" property="id" />
    <result column="role_name" jdbcType="VARCHAR" property="roleName" />
    <result column="enabled" jdbcType="INTEGER" property="enabled" />
    <result column="create_by" jdbcType="BIGINT" property="createBy" />
    <result column="create_time" jdbcType="TIMESTAMP" property="createTime" />
  </resultMap>
</mapper>

4.association标签的嵌套查询 （子查询）