MyBatis-Plus的入门

MyBatis-Plus的入门

Pom依赖

<?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">
    <!-- pom模型版本 -->
    <modelVersion>4.0.0</modelVersion>

    <!-- 项目信息 -->
    <groupId>com.mad</groupId>              <!-- 项目唯一标识 -->
    <artifactId>mybatis-plus</artifactId>   <!-- 项目名 -->
    <version>1.0-SNAPSHOT</version>         <!-- 版本 -->
    <packaging>jar</packaging>              <!-- 打包方式 （pom,war,jar） -->

    <!-- 定义父目录继承关系 -->
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.2.RELEASE</version>
    </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>
        <!--mybatis-plus-->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.3.0</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>2.0.2.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.1.9</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.8</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <!-- maven插件 -->
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>2.0.2.RELEASE</version>
            </plugin>
        </plugins>
    </build>
</project>

项目结构

配置文件

application.properties

#定义服务器端口
server.port=8080
#定义tomcat语言编码
server.tomcat.uri-encoding=utf-8

spring.datasource.driverClassName=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=root
spring.datasource.password=root

SpringBoot启动类

在 Spring Boot 启动类中添加 @MapperScan 注解，扫描 Mapper 文件夹

package com.mad;


import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@MapperScan(value = "com.mad.mapper")
public class MyBatisPlusApplication {

    public static void main(String[] args) {
        SpringApplication.run(MyBatisPlusApplication.class,args);
    }
}

实体类Student

// 由于此处类名与表名一致，未使用注解指定表名
// @TableName(value = "tb_name")
@Data
public class Student {
    // value与数据库主键列名一致，若实体类属性名与表主键列名一致可省略value
    @TableId(value = "sid",type = IdType.AUTO)  //指定自增策略
    private Integer sid;

    private String sname;

    private Integer age;

    private String sex;

    private String department;

    private String address;

    private String birthplace;
}

Mapper文件

package com.mad.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.mad.entity.Student;

public interface StudentMapper extends BaseMapper<Student> {

}

测试类（单表操作）

实际测试时直接使用注解 @SpringBootTest ，studentMapper会注入失败，需要指定classes = MyBatisPlusApplication.class
其中 students.forEach(System.out::println); 是JDK8新增的语法，类似 lambda的语法糖
此版本的条件查询使用的是QueryWrapper，之前的版本是EntityMapper

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.conditions.update.UpdateWrapper;
import com.baomidou.mybatisplus.core.metadata.OrderItem;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.mad.MyBatisPlusApplication;
import com.mad.entity.Student;
import com.mad.mapper.StudentMapper;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

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


@RunWith(SpringRunner.class)
@SpringBootTest(classes = MyBatisPlusApplication.class)
public class SampleTest {
    @Autowired
    StudentMapper studentMapper;

    // mybatis-plus的单表操作
    @Test
    public void test(){
        // 根据id查询时需要给实体类的对应主键的属性添加注解 @TableId
        // 1、根据id查询单条
        Student student = studentMapper.selectById(1);
        System.out.println(student);
        
        // 2、根据id批量查询
        List<Integer> idList = new ArrayList<>();
        idList.add(2);
        idList.add(3);
        List<Student> ids = studentMapper.selectBatchIds(idList);
        ids.forEach(i -> System.out.println("根据id批量查询:"+i));
        
        // 3、无条件查询所有数据
        List<Student> students = studentMapper.selectList(null);
//        students.forEach(System.out::println);
        students.forEach(i -> System.out.println("无条件查询所有数据:"+i));
        
        // 4、使用Map封装条件参数查询
        Map<String,Object> map = new HashMap<>();
        map.put("sname","小王");
        map.put("age",18);
        List<Student> mapList = studentMapper.selectByMap(map);
        mapList.forEach(i -> System.out.println("使用Map封装条件参数查询:"+i));
        
        // 5、无条件分页查询
        Page<Student> studentPage = studentMapper.selectPage(new Page<>(1, 3), null);
        List<Student> records = studentPage.getRecords();
        List<OrderItem> orders = studentPage.getOrders();
        records.forEach(i -> System.out.println("无条件分页查询:"+i));
        orders.forEach(i -> System.out.println("无条件分页查询orders:"+i));
        
        // 6、条件查询单条数据(若查询结果为多条则报错：TooManyResultsException: Expected one result (or null) to be returned by selectOne(), but found: 2)
        Student wrapper01 = studentMapper.selectOne(new QueryWrapper<Student>()
                .eq("sname", "小王")
                .like("department", "信息")
                .eq("sid",1));
        System.out.println("条件查询单条数据:"+wrapper01);
        
        // 7、条件查询多条数据 且 指定结果集
        List<Student> wrapper02 = studentMapper.selectList(new QueryWrapper<Student>()
                .select("sname", "address")
                .between("age", 20, 25)
                .ne("sex", "女"));
        wrapper02.forEach(i -> System.out.println("条件查询多条数据-指定结果集:"+i));
        
        // 8、根据id更新
        Student update01 = new Student();
        update01.setSid(1);
        update01.setDepartment("信息工程");
        studentMapper.updateById(update01);
        
        // 9、根据条件更新
        Student update02 = new Student();
        update02.setAddress("四川");
        studentMapper.update(update02 , new UpdateWrapper<Student>()
                .eq("address","重庆"));
        // delete 和 insert 同理，可根据方法名直接理解如何使用
    }
}