09- 条件查询器 Wrapper

@Test

public void testWrapper2() {

//查询 name=Tom 的用户

QueryWrapper<User> wrapper = new QueryWrapper<>();

wrapper.eq("name","Tom");

//查询一个数据 selectOne，若查询出多个会报错

//Expected one result (or null) to be returned by selectOne(), but found: *

//若出现多个结果使用 list 或 map

User user = userMapper.selectOne(wrapper);//查询一个数据，若出现多个结果使用 list 或 map

System.out.println(user);

}

测试三

@Test

public void testWrapper3() {

//查询 age 在 10-20 之间的用户

QueryWrapper<User> wrapper = new QueryWrapper<>();

wrapper.between("age", 10, 25);//区间

Integer count = userMapper.selectCount(wrapper);//输出查询的数量 selectCount

System.out.p 《一线大厂 Java 面试题解析+后端开发学习笔记+最新架构讲解视频+实战项目源码讲义》无偿开源 威信搜索公众号【编程进阶路】 rintln(count);

}

测试四

@Test

public void testWrapper4() {

//模糊查询

QueryWrapper<User> wrapper = new QueryWrapper<>();

wrapper

.notLike("name","e") //不包含

.likeRight("email","t");//t%

List<Map<String, Object>> maps = userMapper.selectMaps(wrapper);

maps.forEach(System.out::println);

}

测试五

@Test

public void testWrapper5() {

//模糊查询

// SELECT id,name,age,email,version,deleted,create_time,update_time

//FROM user

//WHERE deleted=0 AND id IN

//(select id from user where id<5)

QueryWrapper<User> wrapper = new QueryWrapper<>();

//id 在子查询中查出来

wrapper.inSql("id","select id from user where id<5");

List<Object> objects = userMapper.selectObjs(wrapper);

objects.forEach(System.out::println);