MyBatis-Plus怎么实现多表联查
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建库建表
DROP DATABASE IF EXISTS mp; CREATE DATABASE mp DEFAULT CHARACTER SET utf8; USE mp; DROP TABLE IF EXISTS `t_user`; DROP TABLE IF EXISTS `t_blog`; SET NAMES utf8mb4; CREATE TABLE `t_user` ( `id` BIGINT(0) NOT NULL AUTO_INCREMENT, `user_name` VARCHAR(64) NOT NULL COMMENT '用户名（不能重复）', `nick_name` VARCHAR(64) NOT NULL COMMENT '昵称（可以重复）', `email` VARCHAR(64) COMMENT '邮箱', `create_time` DATETIME(0) NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间', `update_time` DATETIME(0) NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '修改时间', `deleted_flag` BIGINT(0) NOT NULL DEFAULT 0 COMMENT '0：未删除 其他：已删除', PRIMARY KEY (`id`) USING BTREE, UNIQUE KEY `index_user_name_deleted_flag`(`user_name`, `deleted_flag`), KEY `index_create_time`(`create_time`) ) ENGINE = InnoDB COMMENT = '用户'; CREATE TABLE `t_blog` `id` BIGINT(0) NOT NULL AUTO_INCREMENT, `user_id` BIGINT(0) NOT NULL, `user_name` VARCHAR(64) NOT NULL, `title` VARCHAR(256) CHARACTER SET utf8mb4 NOT NULL COMMENT '标题', `description` VARCHAR(256) CHARACTER SET utf8mb4 NOT NULL COMMENT '摘要', `content` LONGTEXT CHARACTER SET utf8mb4 NOT NULL COMMENT '内容', KEY `index_user_id`(`user_id`), ) ENGINE = InnoDB CHARACTER SET = utf8mb4 COMMENT = '博客'; INSERT INTO `t_user` VALUES (1, 'knife', '刀刃', 'abc@qq.com', '2021-01-23 09:33:36', '2021-01-23 09:33:36', 0); INSERT INTO `t_user` VALUES (2, 'sky', '天蓝', '123@qq.com', '2021-01-24 18:12:21', '2021-01-24 18:12:21', 0); INSERT INTO `t_blog` VALUES (1, 1, 'knife', 'Java中枚举的用法', '本文介绍Java的枚举类的使用', '2021-01-23 11:33:36', '2021-01-23 11:33:36', 0); INSERT INTO `t_blog` VALUES (2, 1, 'knife', 'Java中泛型的用法', '本文介绍Java的泛型的使用。', '2021-01-28 23:37:37', '2021-01-28 23:37:37', 0); INSERT INTO `t_blog` VALUES (3, 1, 'knife', 'Java的HashMap的原理', '本文介绍Java的HashMap的原理。', '2021-05-28 09:06:06', '2021-05-28 09:06:06', 0); INSERT INTO `t_blog` VALUES (4, 1, 'knife', 'Java中BigDecimal的用法', '本文介绍Java的BigDecimal的使用。', '2021-06-24 20:36:54', '2021-06-24 20:36:54', 0); INSERT INTO `t_blog` VALUES (5, 1, 'knife', 'Java中反射的用法', '本文介绍Java的反射的使用。', '2021-10-28 22:24:18', '2021-10-28 22:24:18', 0); INSERT INTO `t_blog` VALUES (6, 2, 'sky', 'Vue-cli的使用', 'Vue-cli是Vue的一个脚手架工具', 'Vue-cli可以用来创建vue项目', '2021-02-23 11:34:36', '2021-02-25 14:33:36', 0); INSERT INTO `t_blog` VALUES (7, 2, 'sky', 'Vuex的用法', 'Vuex是vue用于共享变量的插件', '一般使用vuex来共享变量', '2021-03-28 23:37:37', '2021-03-28 23:37:37', 0);
依赖
pom.xml
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.example</groupId> <artifactId>MyBatis-Plus_Multiple</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>MyBatis-Plus_Multiple</name> <description>Demo project for Spring Boot</description> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.3.12.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>1.8</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <scope>runtime</scope> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> <groupId>com.baomidou</groupId> <artifactId>mybatis-plus-boot-starter</artifactId> <version>3.5.1</version> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <groupId>com.github.xiaoymin</groupId> <artifactId>knife4j-spring-boot-starter</artifactId> <version>3.0.3</version> </dependencies> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <!-- 指定maven编译的jdk版本。若不指定,maven3默认用jdk 1.5 maven2默认用jdk1.3 --> <configuration> <source>8</source> <target>8</target> </configuration> </plugin> </plugins> </build> </project>
配置
application.yml
spring: datasource: driver-class-name: com.mysql.cj.jdbc.Driver url: jdbc:mysql://127.0.0.1:3306/mp?serverTimezone=Asia/Shanghai&useUnicode=true&characterEncoding=utf8&useSSL=false password: 222333 username: root #mybatis-plus配置控制台打印完整带参数SQL语句 mybatis-plus: configuration: log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
MyBatis-Plus分页插件配置
package com.example.demo.config;
import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
@Configuration
public class MyBatisPlusConfig {
/**
* 分页插件
*/
@Bean
public MybatisPlusInterceptor mybatisPlusInterceptor() {
MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
return interceptor;
}
}
代码
VO
package com.example.demo.business.blog.vo;
import lombok.Data;
import java.time.LocalDateTime;
@Data
public class BlogVO {
private Long id;
private Long userId;
private String userName;
/**
* 标题
*/
private String title;
* 摘要
private String description;
* 内容
private String content;
* 创建时间
private LocalDateTime createTime;
* 修改时间
private LocalDateTime updateTime;
* 昵称（这个是t_user的字段）
private String nickName;
}
Mapper
package com.example.demo.business.blog.mapper;
import com.baomidou.mybatisplus.core.conditions.Wrapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.example.demo.business.blog.entity.Blog;
import com.example.demo.business.blog.vo.BlogVO;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import org.springframework.stereotype.Repository;
import java.util.List;
@Repository
public interface BlogMapper extends BaseMapper<Blog> {
/**
* 静态查询
*/
@Select("SELECT t_user.user_name " +
" FROM t_blog, t_user " +
" WHERE t_blog.id = #{id} " +
" AND t_blog.user_id = t_user.id")
String findUserNameByBlogId(@Param("id") Long id);
* 动态查询
@Select("SELECT * " +
" ${ew.customSqlSegment} ")
IPage<BlogVO> findBlog(IPage<BlogVO> page, @Param("ew") Wrapper wrapper);
}
Controller
package com.example.demo.business.blog.controller;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.example.demo.business.blog.mapper.BlogMapper;
import com.example.demo.business.blog.vo.BlogVO;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@Api(tags = "自定义SQL")
@RestController
@RequestMapping("/blog")
public class BlogController {
@Autowired
private BlogMapper blogMapper;
@ApiOperation("静态查询")
@GetMapping("staticQuery")
public String staticQuery() {
return blogMapper.findUserNameByBlogId(1L);
}
@ApiOperation("动态查询")
@GetMapping("dynamicQuery")
public IPage<BlogVO> dynamicQuery(Page<BlogVO> page, String nickName, String title) {
QueryWrapper<BlogVO> queryWrapper = new QueryWrapper<>();
queryWrapper.like(StringUtils.hasText(nickName), "t_user.nick_name", nickName);
queryWrapper.like(StringUtils.hasText(title), "t_blog.title", title);
queryWrapper.eq("t_blog.deleted_flag", 0);
queryWrapper.eq("t_user.deleted_flag", 0);
queryWrapper.apply("t_blog.user_id = t_user.id");
return blogMapper.findBlog(page, queryWrapper);
}
测试
访问knife4j页面：http://localhost:8080/doc.html
1.静态查询
2.动态查询
1.不传条件
结果：（可以查到所有数据）
后端输出
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@60bbb9ec] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@1853643659 wrapping com.mysql.cj.jdbc.ConnectionImpl@6a43d29c] will not be managed by Spring
==> Preparing: SELECT COUNT(*) AS total FROM t_blog, t_user WHERE (t_blog.deleted_flag = ? AND t_user.deleted_flag = ? AND t_blog.user_id = t_user.id)
==> Parameters: 0(Integer), 0(Integer)
<== Columns: total
<== Row: 7
<== Total: 1
==> Preparing: SELECT * FROM t_blog, t_user WHERE (t_blog.deleted_flag = ? AND t_user.deleted_flag = ? AND t_blog.user_id = t_user.id) LIMIT ?
==> Parameters: 0(Integer), 0(Integer), 10(Long)
<== Columns: id, user_id, user_name, title, description, content, create_time, update_time, deleted_flag, id, user_name, nick_name, email, create_time, update_time, deleted_flag
<== Row: 1, 1, knife, Java中枚举的用法, 本文介绍Java的枚举类的使用, <<BLOB>>, 2021-01-23 11:33:36, 2021-01-23 11:33:36, 0, 1, knife, 刀刃, abc@qq.com, 2021-01-23 09:33:36, 2021-01-23 09:33:36, 0
<== Row: 2, 1, knife, Java中泛型的用法, 本文介绍Java的泛型的使用。, <<BLOB>>, 2021-01-28 23:37:37, 2021-01-28 23:37:37, 0, 1, knife, 刀刃, abc@qq.com, 2021-01-23 09:33:36, 2021-01-23 09:33:36, 0
<== Row: 3, 1, knife, Java的HashMap的原理, 本文介绍Java的HashMap的原理。, <<BLOB>>, 2021-05-28 09:06:06, 2021-05-28 09:06:06, 0, 1, knife, 刀刃, abc@qq.com, 2021-01-23 09:33:36, 2021-01-23 09:33:36, 0
<== Row: 4, 1, knife, Java中BigDecimal的用法, 本文介绍Java的BigDecimal的使用。, <<BLOB>>, 2021-06-24 20:36:54, 2021-06-24 20:36:54, 0, 1, knife, 刀刃, abc@qq.com, 2021-01-23 09:33:36, 2021-01-23 09:33:36, 0
<== Row: 5, 1, knife, Java中反射的用法, 本文介绍Java的反射的使用。, <<BLOB>>, 2021-10-28 22:24:18, 2021-10-28 22:24:18, 0, 1, knife, 刀刃, abc@qq.com, 2021-01-23 09:33:36, 2021-01-23 09:33:36, 0
<== Row: 6, 2, sky, Vue-cli的使用, Vue-cli是Vue的一个脚手架工具, <<BLOB>>, 2021-02-23 11:34:36, 2021-02-25 14:33:36, 0, 2, sky, 天蓝, 123@qq.com, 2021-01-24 18:12:21, 2021-01-24 18:12:21, 0
<== Row: 7, 2, sky, Vuex的用法, Vuex是vue用于共享变量的插件, <<BLOB>>, 2021-03-28 23:37:37, 2021-03-28 23:37:37, 0, 2, sky, 天蓝, 123@qq.com, 2021-01-24 18:12:21, 2021-01-24 18:12:21, 0
<== Total: 7
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@60bbb9ec]
2.传条件
只传：nickName：刀
结果
后端结果
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@30026aab] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@2127441980 wrapping com.mysql.cj.jdbc.ConnectionImpl@6a43d29c] will not be managed by Spring
==> Preparing: SELECT COUNT(*) AS total FROM t_blog, t_user WHERE (t_user.nick_name LIKE ? AND t_blog.deleted_flag = ? AND t_user.deleted_flag = ? AND t_blog.user_id = t_user.id)
==> Parameters: %刀%(String), 0(Integer), 0(Integer)
<== Columns: total
<== Row: 5
<== Total: 1
==> Preparing: SELECT * FROM t_blog, t_user WHERE (t_user.nick_name LIKE ? AND t_blog.deleted_flag = ? AND t_user.deleted_flag = ? AND t_blog.user_id = t_user.id) LIMIT ?
==> Parameters: %刀%(String), 0(Integer), 0(Integer), 10(Long)
<== Columns: id, user_id, user_name, title, description, content, create_time, update_time, deleted_flag, id, user_name, nick_name, email, create_time, update_time, deleted_flag
<== Row: 1, 1, knife, Java中枚举的用法, 本文介绍Java的枚举类的使用, <<BLOB>>, 2021-01-23 11:33:36, 2021-01-23 11:33:36, 0, 1, knife, 刀刃, abc@qq.com, 2021-01-23 09:33:36, 2021-01-23 09:33:36, 0
<== Row: 2, 1, knife, Java中泛型的用法, 本文介绍Java的泛型的使用。, <<BLOB>>, 2021-01-28 23:37:37, 2021-01-28 23:37:37, 0, 1, knife, 刀刃, abc@qq.com, 2021-01-23 09:33:36, 2021-01-23 09:33:36, 0
<== Row: 3, 1, knife, Java的HashMap的原理, 本文介绍Java的HashMap的原理。, <<BLOB>>, 2021-05-28 09:06:06, 2021-05-28 09:06:06, 0, 1, knife, 刀刃, abc@qq.com, 2021-01-23 09:33:36, 2021-01-23 09:33:36, 0
<== Row: 4, 1, knife, Java中BigDecimal的用法, 本文介绍Java的BigDecimal的使用。, <<BLOB>>, 2021-06-24 20:36:54, 2021-06-24 20:36:54, 0, 1, knife, 刀刃, abc@qq.com, 2021-01-23 09:33:36, 2021-01-23 09:33:36, 0
<== Row: 5, 1, knife, Java中反射的用法, 本文介绍Java的反射的使用。, <<BLOB>>, 2021-10-28 22:24:18, 2021-10-28 22:24:18, 0, 1, knife, 刀刃, abc@qq.com, 2021-01-23 09:33:36, 2021-01-23 09:33:36, 0
<== Total: 5
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@30026aab]
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