mybatis plus的3种查询方式(小结)

本文是基于springboot框架下的查询。

一：基本配置：

1.仓库依赖

<repositories> <repository> <id>alimaven</id> <name>aliyun maven</name> <url>http://maven.aliyun.com/nexus/content/groups/public/</url> <releases> <enabled>true</enabled> </releases> <snapshots> <enabled>false</enabled> </snapshots> </repository></repositories><pluginRepositories> <pluginRepository> <id>alimaven</id> <name>aliyun maven</name> <url>http://maven.aliyun.com/nexus/content/groups/public/</url> <releases> <enabled>true</enabled> </releases> <snapshots> <enabled>false</enabled> </snapshots> </pluginRepository></pluginRepositories>

2.springboot框架依赖

<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <!--添加thymeleaf依赖--> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-thymeleaf</artifactId> </dependency> <!--mybatis持久层org映射框架--> <dependency> <groupId>com.baomidou</groupId> <artifactId>mybatis-plus-boot-starter</artifactId> <version>3.3.1.tmp</version> </dependency>

3.数据库依赖

<dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> </dependency>

二. 三种查询方式

1.like对象查询 (Dept为数据库表,return index为返回的前端页面)

public String index( String name, Model model) { QueryWrapper<Dept> queryWrapper= new QueryWrapper<>();if (name!=null && name.trim().length()>0){ queryWrapper.like('name', name.trim()); } List<Dept> list = deptService.list(queryWrapper); model.addAttribute('list',list); model.addAttribute('name',name); return 'index'; }

1.1 Dao层注解控制台输出sql语句

@Select('select * from dept where name like #{name}')；

2.mybatis注解查询

public String index( String name, Model model) { List<Dept> depts=null; if (name!=null && name.trim().length()>0){ depts = deptService.list2like('%' + name + '%'); }else{ depts=deptService.list(); } model.addAttribute('list', depts); model.addAttribute('name', name); return 'index';}

3.mybatis xml查询

3.1 配置扫描xml文件

mybatis-plus: mapper-locations: classpath:/mapper/*.xml

3.2定义mapper模板

<?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='包对应的Dao类'> <!-- list2likeXml 方法名 resultType 返回结果的类型 --> <select resultType='com.kede.springbootdemo4dept.entity.Dept'> select * from dept <where> <if test='name !=null and name != ’’'>and name like concat(’%’,#{name},’%’) </if> </where> </select></mapper>

3.3controller层代码

public String index( String name, Model model) { List<Dept> depts= deptService.list2likeXml(name); model.addAttribute('list', depts); model.addAttribute('name', name); return 'index';}

4.Dao层的方法

public interface DeptDao extends BaseMapper<Dept> { //org.apache.ibatis.annotations.Param 类似于springmvc里面的@RequestParam //#{name} 和@Param('name') 对应 @Select('select * from dept where name like #{name}')//sql语句，从部门表搜素相关 List<Dept> list2like(@Param('name') String name); List<Dept> list2likeXml(String name);}

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