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前置配置文章

一、wapper介绍

        wrapper的继承体系：

• Wrapper ： 条件构造抽象类，最顶端父类
  • AbstractWrapper ： 用于查询条件封装，生成 sql 的 where 条件
    • QueryWrapper ： 查询条件封装
    • UpdateWrapper ： Update条件封装
  • AbstractLambdaWrapper ： 使用Lambda语法
    • LambdaQueryWrapper ：用于Lambda语法使用的查询Wrapper
    • LambdaUpdateWrapper ： Lambda更新封装Wrapper

二、QueryWrapper

        1.常用方法

        2.关于QueryWrapper的一些测试案例

package com.qcby;import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.qcby.SpringBoot.mapper.UserMapper;
import com.qcby.SpringBoot.pojo.User;
import com.qcby.SpringBoot.service.UserService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;import java.util.*;@SpringBootTestpublic class MybatisPlusTest {@Autowired    private UserMapper userMapper;//测试条件构造器    @Test    public void test01(){//查询用户名包含a，年龄在20到30之间，并且邮箱不为null的用户信息        //SELECT id,username AS name,age,email,is_deleted FROM t_user WHERE is_deleted=0 AND (username LIKE ? AND age BETWEEN ? AND ? AND email IS NOT NULL)        QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.like("name", "a").between("age", 20, 30).isNotNull("email");List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}@Test    public void test02(){//按年龄降序查询用户，如果年龄相同则按id升序排列        //SELECT id,username AS name,age,email,is_deleted FROM t_user WHERE is_deleted=0 ORDER BY age DESC,id ASC        QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.orderByDesc("age").orderByAsc("id");List<User> users = userMapper.selectList(queryWrapper);users.forEach(System.out::println);}@Test    public void test03(){//删除email为空的用户，并非真正的删除，而是逻辑删除        //DELETE FROM t_user WHERE (email IS NULL)        QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.isNull("email");//条件构造器也可以构建删除语句的条件        int result = userMapper.delete(queryWrapper);System.out.println("受影响的行数：" + result);}@Test    public void test04() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();//将（年龄大于20并且用户名中包含有a）或邮箱为null的用户信息修改        //UPDATE t_user SET age=?, email=? WHERE (username LIKE ? AND age > ? OR email IS NULL)        queryWrapper                .like("name", "a").gt("age", 20).or().isNull("email");User user = new User();user.setAge(18);user.setEmail("user@atguigu.com");int result = userMapper.update(user, queryWrapper);System.out.println("受影响的行数：" + result);}@Test    public void test05() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();//将用户名中包含有a并且（年龄大于20或邮箱为null）的用户信息修改        //UPDATE t_user SET age=?, email=? WHERE (username LIKE ? AND (age > ? OR email IS NULL))        //lambda表达式内的逻辑优先运算        //lambda中的i仍然表示该wrapper对象        queryWrapper.like("name", "a").and(i -> i.gt("age", 20).or().isNull("email"));User user = new User();user.setAge(18);user.setEmail("user@atguigu.com");int result = userMapper.update(user, queryWrapper);System.out.println("受影响的行数：" + result);}@Testpublic void test06() {//查询用户信息的username和age字段    //SELECT username,age FROM t_user    QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.select("name", "age");//selectMaps()返回Map集合列表，通常配合select()使用，避免User对象中没有被查询到的列值 为null    List<Map<String, Object>> maps = userMapper.selectMaps(queryWrapper); maps.forEach(System.out::println);}@Testpublic void test07() {//查询id小于等于3的用户信息    //SELECT id,username AS name,age,email,is_deleted FROM t_user WHERE (id IN (select id from t_user where id <= 3))    QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.inSql("id", "select id from t_user where id <= 3");List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}
}

        3.UpdateWrapper

@Testpublic 
void test08() {//将（年龄大于20或邮箱为null）并且用户名中包含有a的用户信息修改    //组装set子句以及修改条件    UpdateWrapper<User> updateWrapper = new UpdateWrapper<>();//lambda表达式内的逻辑优先运算    updateWrapper            .set("age", 18).set("email", "user@atguigu.com").like("name", "a").and(i -> i.gt("age", 20).or().isNull("email"));//这里必须要创建User对象，否则无法应用自动填充。如果没有自动填充，可以设置为null    //UPDATE t_user SET username=?, age=?,email=? WHERE (username LIKE ? AND (age > ? OR email IS NULL))    //User user = new User();    //user.setName("张三");    //int result = userMapper.update(user, updateWrapper);    //UPDATE t_user SET age=?,email=? WHERE (username LIKE ? AND (age > ? OR email IS NULL))    int result = userMapper.update(null, updateWrapper);System.out.println(result);
}

        4.condition

        条件判断的两种格式：

@Test
public void test09() {//定义查询条件，有可能为null（用户未输入或未选择）    String username = null;Integer ageBegin = 10;Integer ageEnd = 24;QueryWrapper<User> queryWrapper = new QueryWrapper<>();//StringUtils.isNotBlank()判断某字符串是否不为空且长度不为0且不由空白符(whitespace) 构成    if(StringUtils.isNotBlank(username)){queryWrapper.like("name","a");}if(ageBegin != null){queryWrapper.ge("age", ageBegin);}if(ageEnd != null){queryWrapper.le("age", ageEnd);}//SELECT id,username AS name,age,email,is_deleted FROM t_user WHERE (age >= ? AND age <= ?)    List<User> users = userMapper.selectList(queryWrapper);users.forEach(System.out::println);
}
@Test
public void test08UseCondition() {//定义查询条件，有可能为null（用户未输入或未选择）    String username = null;Integer ageBegin = 10;Integer ageEnd = 24;QueryWrapper<User> queryWrapper = new QueryWrapper<>();//StringUtils.isNotBlank()判断某字符串是否不为空且长度不为0且不由空白符(whitespace) 构成    queryWrapper            .like(StringUtils.isNotBlank(username), "name", "a").ge(ageBegin != null, "age", ageBegin).le(ageEnd != null, "age", ageEnd);//SELECT id,username AS name,age,email,is_deleted FROM t_user WHERE (age >= ? AND age <= ?)    List<User> users = userMapper.selectList(queryWrapper);users.forEach(System.out::println);
}

        5.LambdaQueryWrapper和LambdaUpdateWrapper

@Testpublic 
void test11() {//组装set子句    LambdaUpdateWrapper<User> updateWrapper = new LambdaUpdateWrapper<>();updateWrapper            .set(User::getAge, 18).set(User::getEmail, "user@atguigu.com").like(User::getName, "a").and(i -> i.lt(User::getAge, 24).or().isNull(User::getEmail)); //lambda 表达式内的逻辑优先运算    User user = new User();int result = userMapper.update(user, updateWrapper);System.out.println("受影响的行数：" + result);
}