MyBatis-Plus--多表联查(动态查询)--方法/教程/实例

企业开发 2022-04-20 14:42:05 阅读次数: 0

原文网址：MyBatis-Plus--多表联查(动态查询)--方法/教程/实例_IT利刃出鞘的博客-CSDN博客

简介

本文用示例介绍使用MyBatis-Plus进行多表查询的方法，包括静态查询和动态查询。

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',
    `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,
    KEY `index_user_id`(`user_id`),
    KEY `index_create_time`(`create_time`)
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COMMENT = '博客';

INSERT INTO `t_user` VALUES (1, 'knife', '刀刃', '[email protected]', '2021-01-23 09:33:36', '2021-01-23 09:33:36', 0);
INSERT INTO `t_user` VALUES (2, 'sky', '天蓝', '[email protected]', '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',
                             '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。',
                             '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。',
                             '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。',
                             '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。',
                             '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>

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

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.1</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>

        <dependency>
            <groupId>com.github.xiaoymin</groupId>
            <artifactId>knife4j-spring-boot-starter</artifactId>
            <version>3.0.3</version>
        </dependency>
    </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 * " +
            " FROM t_blog, t_user " +
            " ${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, [email protected], 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, [email protected], 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, [email protected], 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, [email protected], 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, [email protected], 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, [email protected], 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, [email protected], 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, [email protected], 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, [email protected], 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, [email protected], 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, [email protected], 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, [email protected], 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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