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Mybatis-plus+通用mapper(tk.mybatis)的使用

作者：向岸看

本文主要介绍了Mybatis-plus+通用mapper(tk.mybatis)的使用，文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值，需要的朋友们下面随着小编来一起学习学习吧<BR>

01 引言

常规的MyBatis操作MySQL步骤

1>创建数据库，创建表

2>创建项目，导入逆向工程相对应的依赖与配置

3>逆向工程创建实体/mapper接口/mapper.xml映射文件

4>导入mybatis依赖，mysql依赖

5>编写测试类，测试mapper接口实现CRUD操作

问题：复杂项目Mybatis太过冗余。项目中，每张表对应一个实体类，对应一个mapper.java接口，也对应一个mapper.xml配置文件。每个mapper，java接口都有重复的增、删、改、查4个基础方法，每一个Mapper.xml都有重复的增、删、改、查4个基础sql语句。使用逆向工程可以解决，但是存在很致命的问题，如果列发生变动，对应的sql改动那就是灾难啦。另外，如果一个项目很复杂，那这些文件就膨胀起来，对项目的加载与维护带来很大挑战。此时不禁想，有没有某种方法可以不写crud方法，不写crud sql语句也能完成crud操作呢?

1）MyBatis与MyBatis-Plus区别

MyBatis：

优点：

缺点：

MyBatis-Plus 是在Mybatis的基础上进行二次开发的具有MyBatis所有功能，也添加了不少好用的功能。

比如 :

2）Mybatis-plus入门案例

 案例一：spring容器版本的案例

1> sql导入：

CREATE TABLE `employee` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `password` varchar(255) DEFAULT NULL,
  `email` varchar(255) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `admin` bit(1) DEFAULT NULL,
  `dept_id` bigint(20) DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC;
INSERT INTO `employee` VALUES (1, 'admin', '1', 'admin@abc.com', 40, b'1', 6);
INSERT INTO `employee` VALUES (2, '赵总', '1', 'zhaoz@langfeiyes.com', 35, b'0', 1);
INSERT INTO `employee` VALUES (3, '赵一明', '1', 'zhaoym@langfeiyes.com', 25, b'0', 1);
INSERT INTO `employee` VALUES (4, '钱总', '1', 'qianz@langfeiyes.com', 31, b'0', 2);
INSERT INTO `employee` VALUES (5, '钱二明', '1', 'qianem@langfeiyes.com', 25, b'0', 2);
INSERT INTO `employee` VALUES (6, '孙总', '1', 'sunz@langfeiyes.com', 35, b'0', 3);
INSERT INTO `employee` VALUES (7, '孙三明', '1', 'sunsm@langfeiyes.com', 25, b'0', 3);
INSERT INTO `employee` VALUES (8, '李总', '1', 'liz@langfeiyes.com', 35, b'0', 4);
INSERT INTO `employee` VALUES (9, '李四明', '1', 'lism@langfeiyes.com', 25, b'0', 4);
INSERT INTO `employee` VALUES (10, '周总', '1', 'zhouz@langfeiyes.com', 19, b'0', 5);
INSERT INTO `employee` VALUES (11, '周五明', '1', 'zhouwm@langfeiyes.com', 25, b'0', 5);
INSERT INTO `employee` VALUES (12, '吴总', '1', 'wuz@langfeiyes.com', 41, b'0', 5);
INSERT INTO `employee` VALUES (13, '吴六明', '1', 'wulm@langfeiyes.com', 33, b'0', 5);
INSERT INTO `employee` VALUES (14, '郑总', '1', 'zhengz@langfeiyes.com', 35, b'0', 3);
INSERT INTO `employee` VALUES (15, '郑七明', '1', 'zhengqm@langfeiyes.com', 25, b'0', 2);
INSERT INTO `employee` VALUES (16, '孙四明', '1', 'sunsim@langfeiyes.com', 25, b'0', 3);
INSERT INTO `employee` VALUES (17, '孙五明', '1', 'sunwm@langfeiyes.com', 25, b'0', 3);
INSERT INTO `employee` VALUES (18, '李五明', '1', 'liwm@langfeiyes.com', 25, b'0', 4);
INSERT INTO `employee` VALUES (19, '李六明', '1', 'lilm@langfeiyes.com', 25, b'0', 4);
INSERT INTO `employee` VALUES (20, '叶子', '1', 'yezi@langfeiyes.com', 0, b'0', 1);

2> 依赖引入：

<properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
    </properties>


    <dependencies>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus</artifactId>
            <version>3.4.3.4</version>
        </dependency>

        <!--数据连接池依赖-->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.2.8</version>
        </dependency>

        <!--mysql驱动依赖-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.22</version>
        </dependency>
        <!--自动生成getter/setter方法依赖-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.16</version>
            <scope>provided</scope>
        </dependency>
        <!--单元测试-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <!--spring测试-->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>5.2.16.RELEASE</version>
        </dependency>

        <!--spring环境依赖包-->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.2.16.RELEASE</version>
        </dependency>
        <!--spring事务依赖包-->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-tx</artifactId>
            <version>5.2.16.RELEASE</version>
        </dependency>
        <!--spring jdbc依赖包-->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
            <version>5.2.16.RELEASE</version>
        </dependency>
        <!--spring 日志依赖包-->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.25</version>
        </dependency>
    </dependencies>

3> 配置数据db.properties、日志文件log4j.properties、spring容器文件spring-context-mybatis.xml

jdbc.url=jdbc:mysql://localhost:3306/mybatis-plus?useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2B8
jdbc.username=root
jdbc.password=123456
jdbc.driverClassName=com.mysql.cj.jdbc.Driver
# Global logging configuration
log4j.rootLogger=ERROR, stdout

# 设置 com.langfeiyes.mp.mapper 包下的日志级别为 TRACE，表示输出该包下所有类的 TRACE 级别的日志信息
log4j.logger.com.example.demo.mapper=TRACE
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:p="http://www.springframework.org/schema/p"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
       xmlns:util="http://www.springframework.org/schema/util"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-3.0.xsd
    http://www.springframework.org/schema/util
    http://www.springframework.org/schema/util/spring-util-3.0.xsd">

    <!-- 加载配置属性文件 -->
    <context:property-placeholder location="classpath:db.properties" ignore-unresolvable="true" />
    <!-- 配置数据源 -->
    <bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close">
        <property name="driverClassName" value="${jdbc.driverClassName}"></property>
        <property name="username" value="${jdbc.username}"></property>
        <property name="password" value="${jdbc.password}"></property>
        <property name="url" value="${jdbc.url}"></property>
    </bean>
    <!-- 配置SessionFactory -->
    <bean id="sqlSessionFactory" class="com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"/>
    </bean>
    <!-- MyBatis 动态扫描  -->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.langfeiyes.mp.mapper"/>
    </bean>
</beans>

 3> 编写Employee实体类与mapper接口

Employee.java 

package com.example.demo.domain;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Setter
@Getter
@ToString
public class Employee {
    private Long id;
    private String name;
    private String password;
    private String email;
    private int age;
    private int admin;
    private Long deptId;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public int getAdmin() {
        return admin;
    }

    public void setAdmin(int admin) {
        this.admin = admin;
    }

    public Long getDeptId() {
        return deptId;
    }

    public void setDeptId(Long deptId) {
        this.deptId = deptId;
    }
}

 EmployeeMapper.java

package com.example.demo.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.demo.domain.Employee;

/**
 *
 * 持久层映射接口：mybatis-plus
 * mybatis-plus mapper接口自定义
 * 1：自定义一个接口， 继承BaseMapper
 * BaseMapper接口通常定义了对数据库表的基本 CRUD（Create, Read, Update, Delete）操作，以及其他常用的查询方法
 * 2：指定接口泛型：当前接口操作实体对象：Employee
 *
 */

public interface EmployeeMapper extends BaseMapper<Employee> {

}

4> 编写测试类

package com.example.demo;

import com.example.demo.domain.Employee;
import com.example.demo.mapper.EmployeeMapper;
import org.junit.jupiter.api.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;


@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration({"classpath:spring-context-mybatis.xml"})
public class MapperTest {
	@Autowired
	private EmployeeMapper employeeMapper;

	@Test
	public void testSave(){
		Employee employee = new Employee();
		employee.setAdmin(1);
		employee.setAge(18);
		employee.setDeptId(1L);
		employee.setEmail("yezi@langfeiyes.com");
		employee.setName("yezi");
		employee.setPassword("111");
		employeeMapper.insert(employee);
	}
	@Test
	public void testUpdate(){
		Employee employee = new Employee();
		employee.setId(1L);
		employee.setAdmin(1);
		employee.setAge(18);
		employee.setDeptId(1L);
		employee.setEmail("yezi@langfeiyes.com");
		employee.setName("yezi");
		employee.setPassword("111");
		employeeMapper.updateById(employee);
	}
	@Test
	public void testDelete(){
		employeeMapper.deleteById(1L);
	}
	@Test
	public void testGet(){
		System.out.println(employeeMapper.selectById(1L));
	}

	@Test
	public void testList(){
		System.out.println(employeeMapper.selectList(null));
	}
}

案例二：springboot 版本的案例

1> 导入依赖

<?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 https://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>3.2.4</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>mybatis-plus-demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>mybatis-plus-demo</name>
	<description>mybatis-plus-demo</description>
	<properties>
		<java.version>21</java.version>
	</properties>


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

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

		<dependency>
			<groupId>org.mybatis.spring.boot</groupId>
			<artifactId>mybatis-spring-boot-starter</artifactId>
			<version>3.0.3</version>
		</dependency>

		<!--mybatis-plus依赖-->
		<dependency>
			<groupId>com.baomidou</groupId>
			<artifactId>mybatis-plus-boot-starter</artifactId>
			<version>3.5.5</version>
		</dependency>

		<!--数据连接池依赖-->
		<dependency>
			<groupId>com.alibaba</groupId>
			<artifactId>druid-spring-boot-starter</artifactId>
			<version>1.1.17</version>
		</dependency>
		<!--mysql驱动依赖-->
		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<version>8.0.22</version>
		</dependency>
		<!--测试依赖-->
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
		</dependency>
		<!--自动生成getter/setter方法依赖-->
		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
			<version>1.18.30</version>
			<scope>provided</scope>
		</dependency>

	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

 2>  在application.properties文件中配置数据库连接四要素与日志

#mysql
spring.datasource.url=jdbc:mysql://localhost:3306/mybatis-plus?useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2B8
spring.datasource.username=root
spring.datasource.password=admin
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
 
# 配置sql打印日志
mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl

3> 编写Employee实体类与mapper接口（与上个案例一致）

4> 运行testList方法

（不知道，为什么出现中文乱码）

02 原理解析

两个问题： 

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