在Mybatis @Select注解中實現(xiàn)拼寫動態(tài)sql

更新時間：2020年11月30日 14:50:44 作者：apicescn

這篇文章主要介紹了在Mybatis @Select注解中實現(xiàn)拼寫動態(tài)sql，具有很好的參考價值，希望對大家有所幫助。一起跟隨小編過來看看吧

現(xiàn)在隨著mybatis plus的應用，越來越多的弱化了SQL語句，對于單表操作可以說幾乎不需要進行自己編寫SQL語句了，但對于多表查詢操作目前mybatis plus還沒有很好的支持，還需要自己編寫SQL語句，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;
 
/**
 * 基礎數(shù)據(jù)操作對象
 *
 * @author xxx
 * @date 2018/5/18
 */
@Mapper
public interface MenuDAO extends BaseMapper<MenuDO> {
 
 /**
  * 根據(jù)菜單編碼獲得所有下級菜單列表(包括本級)
  * @param menuId 菜單編碼
  * @return 該菜單下的所有菜單列表(包括本級)
  */
 @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); 
}

這樣整個語句基本上都是寫死的,沒有辦法通過參數(shù)動態(tài)拼接SQL語句，在對于相同語句不同參數(shù)來拼接SQL語句是十分不便的,而如果使用xml來配置的話可以用

<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>

但是現(xiàn)在很多公司可能會采用@Select注解方式來編寫SQL語句，而非通過xml 的SQL Mapper，那對于@Select這種該如何做呢？其實很簡單，只是需要用<script>標簽包圍，然后像xml語法一樣書寫即可，無須任何其他類或自定義注解類來完成，具體事例如下：

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;
 
/**
 * 基礎數(shù)據(jù)操作對象
 *
 * @author xxxx
 * @date 2018/5/18
 */
@Mapper
public interface MenuDAO extends BaseMapper<MenuDO> { 
 
 /**
  * 根據(jù)當前用戶權限獲取所有權限內(nèi)的菜單列表（不分頁）
  * @param menuTreeParam 菜單參數(shù)
  * @return 當前用戶權限獲取所有權限內(nèi)的菜單列表
  */
 @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);
}

至此我們就可以像在xml文件里面一樣愉快的動態(tài)拼接你想要的SQL語句了！

注意：

在@Select注解中采用<script>標簽包圍拼接SQL語句時不能在標簽里有>大于或<小于符號出現(xiàn)，否則會報Caused by: org.xml.sax.SAXParseException: 元素內(nèi)容必須由格式正確的字符數(shù)據(jù)或標記組成。需要對這樣的標簽符號進行轉(zhuǎn)義即可。

補充知識：MyBatis + MyBatis Plus + MySQL——查詢語句中字段名為MySQL關鍵字問題解決方案

問題描述

### 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

問題分析

數(shù)據(jù)庫表中將SQL關鍵字作為字段名時，在查詢的時候MySQL無法進行正常查詢。

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>

解決方案

XML

錯誤：DELETE = #{delete}

正確：`DELETE` = #{delete}

注解

在@TableField注解中加入反引號“ ` ”