Mybatis-plus实现数据库的增删改查操作

目录

1、MybatisPlus简介

2、MybatisPlus注解介绍

3、常用方法

4、SpringBoot整合MybatisPlus实现增删改查的一个简单Demo

5、参考资料

---

1、MybatisPlus简介

Mybatis和MybatisPlus都是非常流行的持久层框架。mybatis可以直接在xml或注解中通过SQL语句操作数据库，很是灵活。但是其操作都要通过SQL语句进行，就必须写大量的xml文件或者注解sql语句，很是麻烦。而mybatis-plus就很好的解决了这个问题。

Mybatis-Plus（简称MP）是 Mybatis 的增强工具，在 Mybatis 的基础上只做增强不做改变，为简化开发、提高效率而生。关于mybatis-plus的更多介绍及特性，可以参考mybatis-plus官网。

mybatis-plus已经封装好了一些crud方法，我们不需要再写SQL语句了，直接调用这些方法就行

2、MybatisPlus注解介绍

• @TableId 关联主键，可以通过type属性指定是否自增
• @TableName 通过value属性关联表名，当类名与表名一致时，value属性可省写
• @TableField 关联表字段，如果属性名称与字段名称一致则此注解可以省写（包含驼峰规则）

3、常用方法

MybatisPlus常用方法可以去看BaseMapper这个接口。BaseMapper这个接口里面封装了一些常用的sql。

public interface BaseMapper<T> extends Mapper<T> {
    int insert(T entity);

    int deleteById(Serializable id);

    int deleteByMap(@Param("cm") Map<String, Object> columnMap);

    int delete(@Param("ew") Wrapper<T> wrapper);

    int deleteBatchIds(@Param("coll") Collection<? extends Serializable> idList);

    int updateById(@Param("et") T entity);

    int update(@Param("et") T entity, @Param("ew") Wrapper<T> updateWrapper);

    T selectById(Serializable id);

    List<T> selectBatchIds(@Param("coll") Collection<? extends Serializable> idList);

    List<T> selectByMap(@Param("cm") Map<String, Object> columnMap);

    T selectOne(@Param("ew") Wrapper<T> queryWrapper);

    Integer selectCount(@Param("ew") Wrapper<T> queryWrapper);

    List<T> selectList(@Param("ew") Wrapper<T> queryWrapper);

    List<Map<String, Object>> selectMaps(@Param("ew") Wrapper<T> queryWrapper);

    List<Object> selectObjs(@Param("ew") Wrapper<T> queryWrapper);

    <E extends IPage<T>> E selectPage(E page, @Param("ew") Wrapper<T> queryWrapper);

    <E extends IPage<Map<String, Object>>> E selectMapsPage(E page, @Param("ew") Wrapper<T> queryWrapper);
}

Wrapper为条件查询构造器，QueryWrapper为Wrapper的一个实现方法。主要是用来进行多个where条件的拼接。

例如：

QueryWrapper<Student> queryWrapper = new QueryWrapper<>();
queryWrapper.gt("age", 10).eq("sex", "女"); //年龄大于10且性别为“女"

Wrapper中的方法	含义
ge	大于等于
gt	表示大于
le	小于等于
lt	小于
eq	等于
ne	不等于
between	范围 between("age",20,30); 年龄范围[20,30]

4、SpringBoot整合MybatisPlus实现增删改查的一个简单Demo

源码：https://gitee.com/wulinchun/mybatis-plus.git   (dev分支)

4.1、目录结构

4.2、代码

4.2.1、xml&yml配置

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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.2.RELEASE</version>
        <relativePath/>
    </parent>
    <groupId>org.example</groupId>
    <artifactId>mybatis-plus</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!--Mybatis-Plus -->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.4.0</version>
        </dependency>
        <!--mybatis-plus 代码生成器-->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-generator</artifactId>
            <version>3.4.0</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.20</version>
            <scope>provided</scope>
        </dependency>
        <!--sqlserver依赖-->
        <dependency>
            <groupId>com.microsoft.sqlserver</groupId>
            <artifactId>mssql-jdbc</artifactId>
        </dependency>
        <!--mysql依赖-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.26</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <fork>true</fork>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

application.yml

server:
  port: 8080

spring:
  profiles:
    active: dev  #使用application-dev.yml里面的配置

application-dev.yml

server:
  port: 8080
spring:
  datasource:
    name: mybatis_plus
    url: jdbc:mysql://localhost:3306/mydb?serverTimezone=UTC&characterEncoding=utf8
    username: root
    password: 123456
    driver-class-name: com.mysql.jdbc.Driver
mybatis:
  mapper-locations: classpath:mapper/*.xml #注意：一定要对应mapper映射xml文件的所在路径
  type-aliases-package: com.mybatisplus.entity # 注意：对应实体类的路径

mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl #打印mybatis-plus的sql语句

ScoreMapper.xml

<?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="com.mybatisplus.mapper.IScoreMapper">

</mapper>

StudentMapper.xml

<?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="com.mybatisplus.mapper.IStudentMapper">

</mapper>

 

4.2.2、实体类

Score.java

package com.mybatisplus.entity;

import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * @author: wu linchun
 * @time: 2021/6/6 11:34
 * @description:
 */
@Data
@TableName("t_score")
@NoArgsConstructor
@AllArgsConstructor
public class Score {
    @TableField("sno")
    private int sno;
    @TableField("subject")
    private String subject;
    @TableField("score")
    private int score;
}

Student.java

package com.mybatisplus.entity;

import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.io.Serializable;

/**
 * @author: Wu Linchun
 * @date: 2021/06/04/10:25
 * @Description:
 **/
@Data
@TableName("t_student")
@NoArgsConstructor
@AllArgsConstructor
public class Student implements Serializable {
    @TableId
    @TableField("sno")
    private int sno;
    @TableField("sname")
    private String sname;
    @TableField("age")
    private int age;
    @TableField("sex")
    private String sex;
    @TableField("sclass")
    private String sclass;
}

StudentScoreVO.java 注:该实体类为映射t_student表和t_score表联合查询的结果

package com.mybatisplus.entity.vo;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.io.Serializable;

/**
 * @author: wu linchun
 * @time: 2021/6/6 11:42
 * @description:
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
public class StudentScoreVO implements Serializable {
    @TableField("sno")
    private int sno;
    @TableField("sname")
    private String sname;
    @TableField("subject")
    private String subject;
    @TableField("score")
    private int score;
}

 

4.2.3、接口&实现类

IScoreMapper.java

package com.mybatisplus.mapper;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.mybatisplus.entity.Student;
import com.mybatisplus.entity.vo.StudentScoreVO;
import javafx.scene.control.Pagination;
import org.apache.ibatis.annotations.Select;
import org.springframework.stereotype.Component;

import java.util.List;

/**
 * @description:
 * @author: wu linchun
 * @time: 2021/6/6 11:49
 */
@Component("iScoreMapper")
public interface IScoreMapper extends BaseMapper<StudentScoreVO> {
    /**
     * 获取学生成绩并分页显示
     * @return
     */
    @Select("select tst.sno,tst.sname,tsc.subject,tsc.score from t_student tst,t_score tsc where tst.sno=tsc.sno")
    List<StudentScoreVO> getScore();


    /**
     * 分页显示学生成绩
     * @param
     * @return
     */
    @Select("select tst.sno,tst.sname,tsc.subject,tsc.score from t_student tst,t_score tsc where tst.sno=tsc.sno")
    IPage<StudentScoreVO> getByPage(Page<StudentScoreVO> studentScoreVOPage,QueryWrapper<StudentScoreVO> queryWrapper);


    @Select("select count(*) from t_student tst,t_score tsc where tst.sno=tsc.sno")
    int getCount();
}

IStudentMapper.java

package com.mybatisplus.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.mybatisplus.entity.Student;
import org.apache.ibatis.annotations.Mapper;
import org.springframework.stereotype.Component;

/**
 * @author: Wu Linchun
 * @date: 2021/06/04/14:48
 * @Description:
 **/
@Component("iStudentMapper")
public interface IStudentMapper extends BaseMapper<Student> {
}

IScoreService.java

package com.mybatisplus.service;

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.mybatisplus.entity.vo.StudentScoreVO;
import javafx.scene.control.Pagination;

import java.util.List;

/**
 * @description:
 * @author: wu linchun
 * @time: 2021/6/6 11:55
 */

public interface IScoreService {
    /**
     *
     * @return
     */
    List<StudentScoreVO> getScore();

    /**
     *分页显示
     * @param
     * @return
     */
    IPage<StudentScoreVO> getByPage(Page<StudentScoreVO> studentScoreVOPage, QueryWrapper<StudentScoreVO> queryWrapper);

    /**
     *
     * @return
     */
    int getCount();
}

IStudentService.java

package com.mybatisplus.service;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.mybatisplus.entity.Student;
import org.apache.ibatis.annotations.Mapper;
import org.springframework.stereotype.Repository;

import java.util.List;

/**
 * @author: Wu Linchun
 * @date: 2021/06/04/14:02
 * @Description:
 **/

public interface IStudentService {
    /**
     * 根据唯一性主键进行查询  sno是唯一性主键
     *
     * @param sno
     * @return
     */
    Student getBySno(int sno);

    /**
     * 查询全部
     *
     * @return
     */
    List<Student> getAll();

    /**
     * 根据性别和年龄查询
     *
     * @param sex
     * @param age
     * @return
     */
    List<Student> getBySexAge(String sex, int age);

    /**
     * 范围&多条件查询
     *
     * @param age
     * @return
     */
    List<Student> getStudentsByScope(int age);

    /**
     * 添加学生
     *
     * @param student
     * @return
     */
    int insertStudent(Student student);

    /**
     * 根据指定条件删除
     *
     * @param sno
     * @return
     */
    int deleteBySno(int sno);

    /**
     * 根据多个指定条件删除
     *
     * @param sclass
     * @param sex
     * @return
     */
    int deleteBySclass_sex(String sclass, String sex);

    /**
     * 更新
     *
     * @param student
     * @return
     */
    int updateStudent(Student student);

    /**
     * 获取表中总记录数
     * @return
     */
    int getCount();

}

ScoreServiceImpl.java

package com.mybatisplus.service.impl;

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.mybatisplus.entity.vo.StudentScoreVO;
import com.mybatisplus.mapper.IScoreMapper;
import com.mybatisplus.service.IScoreService;
import javafx.scene.control.Pagination;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;

import java.util.List;

/**
 * @author: wu linchun
 * @time: 2021/6/6 11:56
 * @description:
 */
@Service
public class ScoreServiceImpl implements IScoreService {
    @Autowired
    @Qualifier("iScoreMapper")
    private IScoreMapper iScoreMapper;


    @Override
    public List<StudentScoreVO> getScore() {
        return iScoreMapper.getScore();
    }

    @Override
    public IPage<StudentScoreVO> getByPage(Page<StudentScoreVO> studentScoreVOPage, QueryWrapper<StudentScoreVO> queryWrapper) {
        return iScoreMapper.getByPage(studentScoreVOPage, queryWrapper);
    }


    @Override
    public int getCount() {
        return iScoreMapper.getCount();
    }
}

StudentServiceImpl.java

package com.mybatisplus.service.impl;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.mybatisplus.entity.Student;
import com.mybatisplus.mapper.IStudentMapper;
import com.mybatisplus.service.IStudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @author: Wu Linchun
 * @date: 2021/06/04/14:55
 * @Description:
 **/
@Service
public class StudentServiceImpl implements IStudentService {

    @Autowired
    @Qualifier("iStudentMapper")
    private IStudentMapper iStudentMapper;


    @Override
    public Student getBySno(int sno) {
        return iStudentMapper.selectById(sno);
    }

    @Override
    public List<Student> getAll() {
        return iStudentMapper.selectList(null);
    }


    @Override
    public List<Student> getBySexAge(String sex, int age) {
        Map<String, Object> map = new HashMap<>();
        map.put("sex", sex);
        map.put("age", age);
        return iStudentMapper.selectByMap(map);
    }

    @Override
    public List<Student> getStudentsByScope(int age) {
        QueryWrapper<Student> queryWrapper = new QueryWrapper<>();
        //ge表示大于等于、gt表示大于、le表示小于等于、lt表示小于
        //eq等于、ne不等于
        //between范围 between("age",20,30); 年龄范围20~30
        //查询年龄20-30范围 1.代表字段  2.代表开始值  3.代表结束值
       /* queryWrapper.gt("age",age);

        queryWrapper.gt("age",10); //年龄大于10
        queryWrapper.ge("age",10); //年龄大于等于10
        queryWrapper.le("age",10); //年龄小于等于10
        queryWrapper.lt("age",10); //年龄小于10
        queryWrapper.eq("age",10); //年龄等于10
        queryWrapper.ne("age",10); //年龄不等于10
        queryWrapper.between("age",20,30); //年龄介于20~30之间*/
        queryWrapper.gt("age", 10).eq("sex", "女"); //年龄大于10且性别为“女"
        return iStudentMapper.selectList(queryWrapper);

    }

    @Override
    public int insertStudent(Student student) {
        return iStudentMapper.insert(student);
    }


    @Override
    public int deleteBySno(int sno) {
        QueryWrapper<Student> queryWrapper = new QueryWrapper<>();
        queryWrapper.eq("sno", sno);
        return iStudentMapper.delete(queryWrapper);
    }

    /**
     * 根据班级和性别删除
     *
     * @param sclass
     * @param sex
     * @return
     */
    @Override
    public int deleteBySclass_sex(String sclass, String sex) {
        Map<String, Object> map = new HashMap<>();
        map.put("sclass", sclass);
        map.put("sex", sex);
        return iStudentMapper.deleteByMap(map);
    }

    @Override
    public int updateStudent(Student student) {
        QueryWrapper<Student> queryWrapper = new QueryWrapper<>();
        queryWrapper.eq("sno", student.getSno());
        return iStudentMapper.update(student, queryWrapper);
    }

    @Override
    public int getCount() {
        QueryWrapper<Student> queryWrapper=new QueryWrapper<>();
        queryWrapper.eq("sex","男");
       // return iStudentMapper.selectCount(null);  //null为获取表中总记录数
        return iStudentMapper.selectCount(queryWrapper);  //获取指定条件的记录数
    }
}

 

4.2.4、配置类

MybatisPlusConfig.java

package com.mybatisplus.config;

import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * @author: wu linchun
 * @time: 2021/6/6 12:13
 * @description: mybatis-plus分页插件配置
 */
@Configuration
public class MybatisPlusConfig {
    @Bean
    public PaginationInterceptor paginationInterceptor() {
        return new PaginationInterceptor();
    }

}

 

4.2.5、测试类

MyControllerTest.java

package com.mybatisplus.test;

import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.mybatisplus.entity.Student;
import com.mybatisplus.entity.vo.StudentScoreVO;
import com.mybatisplus.service.IStudentService;
import com.mybatisplus.service.impl.ScoreServiceImpl;
import com.mybatisplus.service.impl.StudentServiceImpl;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.context.web.WebAppConfiguration;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 * @author: wu linchun
 * @time: 2021/6/5 20:31
 * @description:
 */
@RunWith(SpringRunner.class)
@SpringBootTest
//由于是Web项目，Junit需要模拟ServletContext，因此我们需要给我们的测试类加上@WebAppConfiguration。
@WebAppConfiguration
public class MyControllerTest {
    @Autowired
    @Qualifier("studentServiceImpl")
    private StudentServiceImpl studentServiceImpl;

    @Autowired
    @Qualifier("scoreServiceImpl")
    private ScoreServiceImpl scoreServiceImpl;

    @Test
    public void testAdd() {
        int sno = 20160001;
        for (int i = 0; i < 10; i++) {
            Student student = new Student(sno++, "张三", 20, "男", "2016222");
            if (studentServiceImpl.insertStudent(student) == 1) {
                System.out.println("添加成功");
            } else {
                System.out.println("添加失败");
            }
        }
    }

    @Test
    public void testDeleteBySno() {
        if (studentServiceImpl.deleteBySno(20160009) == 1) {
            System.out.println("删除成功");
        } else {
            System.out.println("删除失败");
        }
    }

    @Test
    public void testDeleteBySclass_sex() {
        if (studentServiceImpl.deleteBySclass_sex("2016221", "男") == 1) {
            System.out.println("删除成功");
        } else {
            System.out.println("删除失败");
        }
    }

    @Test
    public void testGetAll() {
        List<Student> studentList = new ArrayList<Student>();
        studentList = studentServiceImpl.getAll();
        for (Student student : studentList) {
            System.out.println(studentList.toString());
        }
    }

    @Test
    public void testGetStudentsByScope() {
        List<Student> studentList = studentServiceImpl.getStudentsByScope(10);
        for (Student student : studentList) {
            System.out.println(studentList.toString());
        }
    }

    @Test
    public void testUpdateStudent() {
        Student student = new Student(20160010, "HHH", 20, "男", "2016222");
        if (studentServiceImpl.updateStudent(student) == 1) {
            System.out.println("更新成功");
        } else {
            System.out.println("更新失败");
        }
    }

    @Test
    public void testGetBySno() {
        Student student = studentServiceImpl.getBySno(20160003);
        System.out.println(student.toString());
    }

    @Test
    public void testGetCount() {
        System.out.println(studentServiceImpl.getCount());
    }

    @Test
    public void testGetScore() {
        List<StudentScoreVO> studentScoreVOList = scoreServiceImpl.getScore();
        for (StudentScoreVO studentScoreVO : studentScoreVOList) {
            System.out.println(studentScoreVO.toString());
        }
    }

    @Test
    public void testGetByPage() {
        int curr = 0, size = 3;
        while (curr <= scoreServiceImpl.getCount() / 3 + 1) {
            Page<StudentScoreVO> page = new Page<>(curr, size);
            System.out.println(curr + " " + size);
            scoreServiceImpl.getByPage(page, null).getRecords().forEach(System.out::println);
            curr++;
            System.out.println("------------------------------------------------");
        }
    }

}

由于在yml中增加了打印MybatisPlus的sql配置，因此执行时可以在控制台看到输出的MybatisPlus封装的sql语句。

 

5、参考资料

MyBatis Plus 简单介绍 - 知乎 (zhihu.com)

mybatis plus实现某种条件查询 - 谢世林 - 博客园 (cnblogs.com)

mybatis-plus的sql语句打印问题_猿,码的博客-CSDN博客_mybatisplus打印sql语句

mybatis-plus实现多表联查 - 白衣风云 - 博客园 (cnblogs.com)

MyBatis-Plus_分页查询_Gblfy_Blog-CSDN博客_mybatis-plus分页查询

Mybatis-plus中sql语句LT、LE、EQ、NE、GE、GT的意思 - 潘向福 - 博客园 (cnblogs.com)