03 条件构造器

条件构造器

十分重要：Wrapper 记住查看输出的SQL进行分析

1、测试一

@Test
public void testWrapper1() {
    //参数是一个wrapper ，条件构造器，和刚才的map对比学习！
    //查询name不为空，email不为空，age大于18的用户
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper
        .isNotNull("name")
        .isNotNull("email")
        .ge("age",18);
    List<User> userList = userMapper.selectList(wrapper);
    userList.forEach(System.out::println);
}

测试二

@Test
public void testWrapper2() {
    //查询name=wsk的用户
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.eq("name","wsk");
    //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, 20);//区间
    Integer count = userMapper.selectCount(wrapper);//输出查询的数量selectCount
    System.out.println(count);
}

测试四

@Test
public void testWrapper4() {
    //模糊查询
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper
        .notLike("name","s")
        .likeRight("email","t");//qq%  左和右？
    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);
}

测试六

@Test
public void testWrapper6() {
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    //通过id进行降序排序
    wrapper.orderByDesc("id");
    List<User> userList = userMapper.selectList(wrapper);
    userList.forEach(System.out::println);
}