<dependency>
? ? <groupId>org.postgresql</groupId>
? ? <artifactId>postgresql</artifactId>
</dependency>
<dependency>
? ? <groupId>org.springframework.boot</groupId>
? ? <artifactId>spring-boot-starter-jdbc</artifactId>
? ? <version>3.0.4</version>
</dependency>
<dependency>
? ? <groupId>org.projectlombok</groupId>
? ? <artifactId>lombok</artifactId>
? ? <version>1.18.26</version>
</dependency>

spring:
  datasource:
    driver-class-name: org.postgresql.Driver
    username: postgres
    password: root
    url: jdbc:postgresql://127.0.0.1:5432/postgres

@Slf4j
@SpringBootTest
class MypgApplicationTests {
? ? @Autowired
? ? JdbcTemplate jdbcTemplate;
? ? @Test
? ? void contextLoads() {
? ? ? ? Long count = jdbcTemplate.queryForObject("select count(*) from test", Long.class);
? ? ? ? log.info("記錄總數(shù)：{}",count);
? ? }
}

<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.3.0</version>
</dependency>

mybatis:
  mapper-locations: classpath:mapper/*.xml
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl 

@Data
public class Test {
? ? private Long id;
}

public interface TestMapper {
? ? Long queryForMybatis(Test testDO);
}

<?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.vainycos.dao.TestMapper">
? ? <select id="queryForMybatis" parameterType="com.vainycos.domain.Test" resultType="java.lang.Long">
? ? ? ? select count(*) from test
? ? ? ? <where>
? ? ? ? ? ? <if test="id != null and id != ''">
? ? ? ? ? ? ? ? and id = #{id}
? ? ? ? ? ? </if>
? ? ? ? </where>
? ? </select>
</mapper>

@Service
public class TestService {
? ? @Resource
? ? private TestMapper testMapper;
? ? public Long queryForMybatis(Test testDO){
? ? ? ? return testMapper.queryForMybatis(testDO);
? ? }
}

@MapperScan("com.vainycos.dao")
@SpringBootApplication
public class MypgApplication {
? ? public static void main(String[] args) {
? ? ? ? SpringApplication.run(MypgApplication.class, args);
? ? }
}

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.4.3</version>
</dependency>

public interface TestMapper extends BaseMapper<Test> {
? ? Long queryForMybatis(Test testDO);
}

public Long queryForMybatisPlus(Test testDO){
    Integer resultCount = testMapper.selectCount(new LambdaQueryWrapper<Test>()
            .eq(testDO.getId() != null, Test::getId, testDO.getId())
    );
    return resultCount.longValue();
}

@GetMapping("/queryForMybatisPlus")
public Long queryForMybatisPlus(Test testDO){
    return testService.queryForMybatisPlus(testDO);
}