<set> tag of MyBatis dynamic SQL

Introduction

In Mybatis, the update statement can use the set label to dynamically update columns. The set tag can dynamically add the set keyword to the SQL statement, and remove the redundant comma appended to the end of the condition.
Function:
automatically add the SET keyword before the first field to be modified
Remove the connector (,) before the first field to be modified

grammar

<set>
</set>

Network case

    <!--使用set元素动态修改一个网站记录 -->
    <update id="updateWebsite"
        parameterType="net.biancheng.po.Website">
        UPDATE website
        <set>
            <if test="name!=null">name=#{name}，</if>
            <if test="url!=null">url=#{url}，</if>
        </set>
        WHERE id=#{id}
    </update>

basic environment

1. Database preparation

# 创建一个名称为t_customer的表
CREATE TABLE t_customer (
    id int(32) PRIMARY KEY AUTO_INCREMENT,
    username varchar(50),
    jobs varchar(50),
    phone varchar(16)
);
# 插入3条数据
INSERT INTO t_customer VALUES ('1', 'joy', 'teacher', '13733333333');
INSERT INTO t_customer VALUES ('2', 'jack', 'teacher', '13522222222');
INSERT INTO t_customer VALUES ('3', 'tom', 'worker', '15111111111');

2. Create a new project or Module

3 Add in 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">
    <parent>
        <artifactId>mybatis</artifactId>
        <groupId>com.example</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.biem</groupId>
    <artifactId>dynamaicSql</artifactId>

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

    <dependencies>
        <!--1.引入mybatis包-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.6</version>
        </dependency>
        <!--2.单元测试-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>

        <!--3.mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.18</version>
            <scope>runtime</scope>
        </dependency>

        <!--4.log4j日志-->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.16</version>
        </dependency>
    </dependencies>
</project>

4. Create package and folder

Create package com.biem.pojo under src/main/java/
com.biem.mapper
com.biem.util
Create folder
com/ biem/mapper under src/main/resources/
Create package
com.biem under src/test/java .test

5 Framework configuration files

5.1 mybatis core configuration file mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!--引入properties文件-->
    <properties resource="jdbc.properties"></properties>

    <!--将下划线映射为驼峰-->
    <settings>
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>

    <!--设置类型别名-->
    <typeAliases>
        <!--
            以包为单位，将包下所有的类型设置设置默认的类型别名，即类名且不区分大小写
        -->
        <package name="com.biem.pojo"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>

    </environments>

    <!-- 引入映射文件 -->
    <mappers>
        <!--
            以包为单位引入映射文件
            要求：
            1. mapper接口所在的包要和映射文件所在的包一致
            2. mapper接口要和映射文件的名字一致
        -->
        <package name="com.biem.mapper"/>
    </mappers>


</configuration>

5.2 mybatis property file jdbc.properties

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC
jdbc.username=root
jdbc.password=root

5.3 log4j.xml file

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

    <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
        <param name="Encoding" value="UTF-8"/>
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) \n"/>
        </layout>
    </appender>
    <logger name="java.sql">
        <level value="debug"/>
    </logger>
    <logger name="org.apache.ibatis">
        <level value="info"/>
    </logger>
    <root>
        <level value="debug"/>
        <appender-ref ref="STDOUT"/>
    </root>
</log4j:configuration>

6 User Profiles

6.1 Entity class

package com.biem.pojo;

import lombok.*;

/**
 * ClassName: Customer
 * Package: com.biem.pojo
 * Description:
 *
 * @Create 2023/4/5 22:17
 * @Version 1.0
 */
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Builder
@ToString
public class Customer {
    
    
    private Integer id;
    private String username;
    private String jobs;
    private String phone;
}

It is necessary to introduce lombok in pom.xml to simplify the code of the original entity class

6.2 mybatis interface class

package com.biem.mapper;

/**
 * ClassName: CustomerMapper
 * Package: com.biem.mapper
 * Description:
 *
 * @Create 2023/4/5 22:19
 * @Version 1.0
 */
public interface CustomerMapper {
    
    
}

6.3 mybatis user configuration file

<?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.biem.mapper.CustomerMapper">
    <!-- namespace要和mapper接口的全类名保持一致，例如com.biem.mybatis.mapper.xxxMapper -->

    <!-- sql语句要和接口的方法名保持一致 -->

</mapper>

6.4 mybatis tool class

package com.biem.util;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;

/**
 * ClassName: MybatisUtil
 * Package: com.biem.utils
 * Description:
 *
 * @Create 2023/4/5 22:23
 * @Version 1.0
 */
public class MybatisUtil {
    
    
    //利用static(静态)属于类不属于对象,且全局唯一
    private static SqlSessionFactory sqlSessionFactory = null;
    //利用静态块在初始化类时实例化sqlSessionFactory
    static {
    
    
        InputStream is= null;
        try {
    
    
            is = Resources.getResourceAsStream("mybatis-config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
        } catch (IOException e) {
    
    
            e.printStackTrace();
            throw new ExceptionInInitializerError(e);
        }
    }

    /**
     * openSession 创建一个新的SqlSession对象
     * @return SqlSession对象
     */
    public static SqlSession openSession(boolean autoCommit){
    
    
        return sqlSessionFactory.openSession(autoCommit);
    }

    public static SqlSession openSession(){
    
    
        return sqlSessionFactory.openSession();
    }
    /**
     * 释放一个有效的SqlSession对象
     * @param session 准备释放SqlSession对象
     */
    public static void closeSession(SqlSession session){
    
    
        if(session != null){
    
    
            session.close();
        }
    }
}

6.5 Test class

package com.biem.test;

import com.biem.mapper.CustomerMapper;
import com.biem.pojo.Customer;
import com.biem.util.MybatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

/**
 * ClassName: TestCustomer
 * Package: com.biem.test
 * Description:
 *
 * @Create 2023/4/5 22:32
 * @Version 1.0
 */
public class TestCustomer {
    
    
}

7 The project structure is as follows

Update records using the set tag

1 Add in com.biem.mapper.CustomerMapper.class

public int updateCustomerBySet(Customer customer);

2 Add in com/biem/mapper/CustomerMapper.xml

    <!--public int updateCustomerBySet(Customer customer);-->
    <update id="updateCustomerBySet" parameterType="customer">
        update t_customer
        <set>
            <if test="username != null and username != ''">
                username=#{username}
            </if>
            <if test="jobs != null and jobs != ''">
                jobs=#{jobs}
            </if>
            <if test="phone != null and phone != ''">
                phone=#{phone}
            </if>
        </set>
        where id = #{id}
    </update>

3. Function test com.biem.test.TestMybatis.java add test method

    @Test
    public void testUpdateCustomerBySet(){
    
    
        // 通过工具类获取SqlSession对象
        SqlSession session = MybatisUtil.openSession();
        // 创建Customer对象，封装需要组合查询的条件
        Customer customer = new Customer();
        customer.setId(3);
        customer.setPhone("15111001100");
        CustomerMapper mapper = session.getMapper(CustomerMapper.class);
        int rows = mapper.updateCustomerBySet(customer);
        if(rows>0){
    
    
            System.out.println("您成功的更新了"+rows+"条记录");
        }else{
    
    
            System.out.println("更新失败");
        }
        // 关闭SqlSession
        session.close();
    }