3.1 select

select(String... sqlSelect)
select(Predicate<TableFieldInfo> predicate)
select(Class<T> entityClass, Predicate<TableFieldInfo> predicate)

设置查询字段
说明:

以上方法分为两类. 第二类方法为:过滤查询字段(主键除外),入参不包含 class 的调用前需要wrapper内的entity属性有值!
这两类方法重复调用以最后一次为准

• 例: select("id", "name", "age")
• 例: select(i -> i.getProperty().startsWith("test"))

4、UpdateWrapper

说明： 继承自 AbstractWrapper ,自身的内部属性 entity 也用于生成 where 条件LambdaUpdateWrapper, 可以通过 new UpdateWrapper().lambda() 方法获取!

4.1 set

set(String column, Object val)
set(boolean condition, String column, Object val)

• SQL SET 字段
• 例: set("name", "老李头")
• 例: set("name", "")—>数据库字段值变为空字符串
• 例: set("name", null)—>数据库字段值变为null

4.2 setSql

setSql(String sql)

• 设置 SET 部分 SQL
• 例: setSql("name = '老李头'")

4.3 lambda

获取 LambdaWrapper
在QueryWrapper中是获取LambdaQueryWrapper
在UpdateWrapper中是获取LambdaUpdateWrapper

5、实例

先创建一个SpringBoot工程

5.1 引入依赖：

<?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>2.5.1</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.baomidou.mybatisplus</groupId>
    <artifactId>mybatisplus01</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>mybatisplus01</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

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

        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.4.3.1</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.alibaba/druid-spring-boot-starter -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.2.6</version>
        </dependency>



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

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

5.2 application.yml

# DataSource Config
spring:
  datasource:
    url: jdbc:mysql://localhost:3306/mp?&useSSL=false&serverTimezone=UTC&allowPublicKeyRetrieval=true
    username: root
    password: 123456
    driver-class-name: com.mysql.cj.jdbc.Driver
    type: com.alibaba.druid.pool.DruidDataSource
# mybatis-plus配置控制台打印sql语句:
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

5.3 Mybatis-plus分页拦截器

@MapperScan注解我加在了SpringBoot的启动类上面，所以这个配置类并没有写

package com.baomidou.mybatisplus.config;

import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MybatisPlusConfig {

    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor(){
        MybatisPlusInterceptor interceptor=new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }
}

5.4 Employee.java

package com.baomidou.mybatisplus.bean;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;

/**
 * @TableName
 *  value:指定当前实体类所对应的表名
 */
@Data
@TableName(value = "tbl_employee")
public class Employee {
    /**
     * @TableId:
     *  value:指定表中的主键列的列名，如果实体属性名和列名一致，可以省略不指定
     *  type:指定主键策略
     */
    @TableId(value = "id",type = IdType.AUTO)
    private Integer id;         //int

    @TableField(value = "last_name")
    private String lastName;

    @TableField(value = "email")
    private String email;

    @TableField(value = "gender")
    private Integer gender;

    @TableField(value = "age")
    private Integer age;

//    @TableField(exist = false)
//    private Double salary;
}

5.5 条件构造器：查询操作

我们需要分页查询tbl_employee表中，年龄在18~50之间且性别为男且姓名为Tom的所有用户

   Page<Employee> employeePage = employeeMapper.selectPage(new Page<Employee>(1, 2),
                new QueryWrapper<Employee>()
                        .between("age", 18, 50)
                        .eq("gender", 1)
                        .eq("last_name", "Tom")
        );
        List<Employee> employeeList=employeePage.getRecords();
        employeeList.forEach(System.out::println);

查询tbl_employee表中性别为女，且名字中带有“老师”或者邮箱中带有‘a’

 List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>()
                .eq("gender", 0)
                .like("last_name", "老师")
                .or()
                .like("email", "a")
        );
        employeeList.forEach(System.out::println);

查询性别为女的，根据age进行排序(asc/desc)

        List<Employee> employeeList = employeeMapper.selectList(
                new QueryWrapper<Employee>()
                        .eq("gender", 0)
//                        .orderBy(true,true,"age")
//                        .orderByDesc("age")
                        .orderByAsc("age")
        );
        employeeList.forEach(System.out::println);

5.6 条件构造器 修改操作

 @Test
    public void testWrapperUpdate(){
        Employee employee=new Employee();
        employee.setLastName("苍老师");
        employee.setEmail("cls@sina.com");
        employee.setGender(0);

        Integer result = employeeMapper.update(employee,
                new UpdateWrapper<Employee>()
                .eq("last_name","Tom")
                .eq("age",45)
        );
        System.out.println("result="+result);
    }

5.7 条件构造器 删除操作

 /**
     * 条件构造器  删除操作
     */
    @Test
    public void testWrapperDelete(){

        Integer result = employeeMapper.delete(new QueryWrapper<Employee>()
                .eq("last_name", "Tom")
                .eq("age", 33)
        );
        System.out.println("result="+result);
    }