MyBatisPlus中條件查詢怎么用Wrapper來構(gòu)建?

增刪改查四個操作中，查詢是非常重要的也是非常復(fù)雜的操作，MyBatisPlus將書寫復(fù)雜的SQL查詢條件進(jìn)行了封裝，使用編程的形式完成查詢條件的組合。 在查詢所有和分頁查詢的時候，都能看到過一個Wrapper類，這個類就是用來構(gòu)建查詢條件的，如下圖所示:

環(huán)境構(gòu)建

在構(gòu)建條件查詢之前，我們先來準(zhǔn)備下環(huán)境： 創(chuàng)建一個SpringBoot項目和pom.xml中添加對應(yīng)的依賴。

<?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>2.5.0</version>
    </parent>
    <groupId>com.itheima</groupId>
    <artifactId>mybatisplus_02_dql</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <properties>
        <java.version>1.8</java.version>
    </properties>
        <dependencies>

        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.4.1</version>
        </dependency>

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

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.16</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

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

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>

        </dependencies>

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

編寫UserDao接口

@Mapper   
public  interface UserDao  extends  BaseMapper<User>  {   
}

編寫模型類

@Data
public class User {
    private Long id;
    private String name;
    private String password;
    private Integer age;
    private String tel;
 }

編寫引導(dǎo)類

@SpringBootApplication
public class Mybatisplus02DqlApplication {

    public static void main(String[] args) {
        SpringApplication.run(Mybatisplus02DqlApplication.class, args);
    }

}

編寫配置文件

# dataSource
spring:
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/mybatisplus_db?serverTimezone=UTC
    username: root
    password: root
# mp日志
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

編寫測試類

@SpringBootTest
class Mybatisplus02DqlApplicationTests {

    @Autowired
    private UserDao userDao;

    @Test
    void testGetAll(){
         List<User> userList = userDao.selectList(null);
         System.out.println(userList);
     }
 }

最終創(chuàng)建的項目結(jié)構(gòu)為:

測試的時候，控制臺打印的日志比較多，速度有點(diǎn)慢而且不利于查看運(yùn)行結(jié)果，所以接下來我們把 這個日志處理下:

取消初始化spring日志打印，resources目錄下添加logback.xml，名稱固定，內(nèi)容如下:

<?xml version="1.0" encoding="UTF-8"?> 
<configuration> 
</configuration>

application.yml添加如下內(nèi)容

# mybatis-plus日志控制臺輸出
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  global-config:
    banner: off # 關(guān)閉mybatisplus啟動圖標(biāo)

取消SpringBoot的log打印

application.yml添加如下內(nèi)容:

spring:
  main:
    banner-mode: off # 關(guān)閉SpringBoot啟動圖標(biāo)(banner)