在Mybatis @Select注解中实现拼写动态sql

现在随着mybatis plus的应用，越来越多的弱化了sql语句，对于单表操作可以说几乎不需要进行自己编写sql语句了，但对于多表查询操作目前mybatis plus还没有很好的支持，还需要自己编写sql语句，如：

import java.util.list; 
import org.apache.ibatis.annotations.mapper;
import org.apache.ibatis.annotations.param;
import org.apache.ibatis.annotations.select;
 
import com.baomidou.mybatisplus.mapper.basemapper;
import com.shield.base.model.domain.menudo;
import com.shield.base.model.param.menutreeparam;
 
/**
 * 基础数据操作对象
 *
 * @author xxx
 * @date 2018/5/18
 */
@mapper
public interface menudao extends basemapper<menudo> {
 
 /**
  * 根据菜单编码获得所有下级菜单列表(包括本级)
  * @param menuid 菜单编码
  * @return 该菜单下的所有菜单列表(包括本级)
  */
 @select("with menutree"
  + " as"
  + "("
  + " select menu1.father_rowid as id,menu1.son_rowid as parentid,menu1.system_name as menuname,"
  + "menu1.system_full_rowid as menutreeflat,menu1.level_value as menulevel,menu1.homepage_status as homestatus,"
  + "menu1.menu_status as menutype,menu1.sort as sort,menu1.duty_name as createname,"
  + "menu1.duty_datetime as createdate,menu1.update_datetime as updatedate,menu1.stop_status as status"
  + " from system_menu_setup menu1 where menu1.father_rowid = #{menuid}"
  + " union all"
  + " select menu2.father_rowid as id,menu2.son_rowid as parentid,menu2.system_name as menuname,"
  + "menu2.system_full_rowid as menutreeflat,menu2.level_value as menulevel,menu2.homepage_status as homestatus,"
  + "menu2.menu_status as menutype,menu2.sort as sort,menu2.duty_name as createname,"
  + "menu2.duty_datetime as createdate,menu2.update_datetime as updatedate,menu2.stop_status as status"
  + " from system_menu_setup menu2"
  + " inner join menutree t on menu2.son_rowid = t.id"
  + ")"
  + " select id,parentid,menuname,menutreeflat,menulevel,homestatus,menutype,sort,createname,"
  + "createdate,updatedate,status from menutree")
 list<menudo> selectmenutreelist(@param(value = "menuid") long menuid); 
}

这样整个语句基本上都是写死的,没有办法通过参数动态拼接sql语句，在对于相同语句不同参数来拼接sql语句是十分不便的,而如果使用xml来配置的话可以用

<where>
 <if test="stopstatus != null">
 and menu.stop_status=#{stopstatus} and rolemenu.stop_status=#{stopstatus}
 </if>
 <if test="menusource != null">
 and menusource.menu_source=#{menusource}
 </if>
 <if test="userid != null">
 and roleuser.operator_rowid=#{userid}
 </if>
</where>

但是现在很多公司可能会采用@select注解方式来编写sql语句，而非通过xml 的sql mapper，那对于@select这种该如何做呢？其实很简单，只是需要用<script>标签包围，然后像xml语法一样书写即可，无须任何其他类或自定义注解类来完成，具体事例如下：

package com.szss.shield.base.dao; 
import java.util.list; 
import org.apache.ibatis.annotations.mapper;
import org.apache.ibatis.annotations.param;
import org.apache.ibatis.annotations.select;
 
import com.baomidou.mybatisplus.mapper.basemapper;
import com.shield.base.model.domain.menudo;
import com.shield.base.model.param.menutreeparam;
 
/**
 * 基础数据操作对象
 *
 * @author xxxx
 * @date 2018/5/18
 */
@mapper
public interface menudao extends basemapper<menudo> { 
 
 /**
  * 根据当前用户权限获取所有权限内的菜单列表（不分页）
  * @param menutreeparam 菜单参数
  * @return 当前用户权限获取所有权限内的菜单列表
  */
 @select("<script>"
  + " with menutree"
  + " as"
  + " ("
  + " select menu.father_rowid as id,menu.son_rowid as parentid,menu.system_name as menuname,\n"
  + " menu.level_value as menulevel,menu.homepage_status as homestatus,\n"
  + " menu.menu_status as menutype,menu.sort as sort,menu.stop_status as status,cast(max(menusource.menu_path_url) as varchar) as menuurl \n"
  + "from system_menu_setup menu \n"
  + " left join system_menu_source_setup menusource\n"
  + " on menu.father_rowid=menusource.system_menu_rowid \n"
  + " left join system_role_custom_menu_setup rolemenu \n"
  + " on menu.father_rowid=rolemenu.system_menu_rowid \n"
  + " left join system_role_operator_setup roleuser \n"
  + " on roleuser.system_role_setup_rowid=rolemenu.system_role_rowid \n"
  + " left join system_role_setup role \n"
  + " on roleuser.system_role_setup_rowid=role.rowid\n"
  + " left join system_department_menu_setup depmenu\n"
  + " on menu.father_rowid=depmenu.system_menu_rowid\n"
  + "<where>"
  + "<if test='stopstatus != null'>"
  + " and menu.stop_status=#{stopstatus} and rolemenu.stop_status=#{stopstatus}\n"
  +"</if>"
  + "<if test='menusource != null'>"
  + " and menusource.menu_source=#{menusource}"
  +"</if>"
  + "<if test='userid != null'>"
  + " and roleuser.operator_rowid=#{userid}\n"
  +"</if>"
  +"</where>"
  + " group by menu.father_rowid ,menu.son_rowid ,menu.system_name,menu.level_value,menu.homepage_status,\n"
  + " menu.menu_status,menu.sort,menu.duty_name,menu.duty_datetime,menu.update_datetime,menu.stop_status\n"
  + " union all\n"
  + " select menu2.father_rowid as id,menu2.son_rowid as parentid,menu2.system_name as menuname,\n"
  + " menu2.level_value as menulevel,menu2.homepage_status as homestatus,\n"
  + " menu2.menu_status as menutype,menu2.sort as sort,menu2.stop_status as status,cast('' as varchar) as menuurl\n"
  + " from system_menu_setup menu2\n"
  + " inner join menutree t on menu2.father_rowid= t.parentid\n"
  + " )\n"
  + " select id,parentid,menuname,menulevel,homestatus,menutype,sort,status,max(menuurl) as menuurl from menutree\n"
  + " group by id,parentid,menuname,menulevel,homestatus,menutype,sort,status\n"
  + " order by menulevel,sort"
  + " </script>")
 list<menudo> selectmenutreelistbyuserid(menutreeparam menutreeparam);
}

至此我们就可以像在xml文件里面一样愉快的动态拼接你想要的sql语句了！

注意：

在@select注解中采用<script>标签包围拼接sql语句时不能在标签里有>大于或<小于符号出现，否则会报caused by: org.xml.sax.saxparseexception: 元素内容必须由格式正确的字符数据或标记组成。需要对这样的标签符号进行转义即可。

补充知识：mybatis + mybatis plus + mysql——查询语句中字段名为mysql关键字问题解决方案

问题描述

### cause: com.mysql.jdbc.exceptions.jdbc4.mysqlsyntaxerrorexception: you have an error in your sql syntax; check the manual that corresponds to your mysql server version for the right syntax to use near 'desc,username,create_time,update_time from test where id=1' at line 1 ; bad sql grammar []; nested exception is com.mysql.jdbc.exceptions.jdbc4.mysqlsyntaxerrorexception: you have an error in your sql syntax; check the manual that corresponds to your mysql server version for the right syntax to use near 'desc,username,create_time,update_time from test where id=1' at line 1] with root cause

com.mysql.jdbc.exceptions.jdbc4.mysqlsyntaxerrorexception: you have an error in your sql syntax; check the manual that corresponds to your mysql server version for the right syntax to use near 'desc,username,create_time,update_time from test where id=1' at line 1

问题分析

数据库表中将sql关键字作为字段名时，在查询的时候mysql无法进行正常查询。

maven
    <dependency>
      <groupid>org.mybatis.spring.boot</groupid>
      <artifactid>mybatis-spring-boot-starter</artifactid>
      <version>2.1.2</version>
    </dependency>
    <!--mybatis-plus-->
    <dependency>
      <groupid>com.baomidou</groupid>
      <artifactid>mybatis-plus-boot-starter</artifactid>
      <version>3.3.1.tmp</version>
    </dependency>

解决方案

xml

错误：delete = #{delete}

正确：`delete` = #{delete}

注解

在@tablefield注解中加入反引号“ ` ”