Mybatis-Plus——条件构造器和常用接口

1、Wrapper介绍

• Wrapper:条件构造类，是父类
  • AbstractWrapper : 用于查询条件的封装，生成sql的where条件
    • QueryWrapper : 查询条件封装
    • UpdateWrapper : Update条件的封装
    • AbstractLambdaWrapper : 使用Lambda语法
      • LambdaQueryWrapper：用于Lambda语法使用的查询Wrapper
      • LambdaUpdateWrapper: 更新封装的Wrapper(Lambda)

2、QueryWrapper使用

①组装查询条件

 @Test
    public void test01(){
    //查询用户名包含a 年龄18-25之间 邮箱信息不为Null的用户信息
    QueryWrapper<User> queryWrapper = new QueryWrapper<User>();
    queryWrapper.like("user_name","a")
                    .between("age",18,25)
                            .isNotNull("email");
        List<User> users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);
    }

②组装排序条件

@Test
public void test02(){
    //将age字段按照降序排序 id字段升序排序
    QueryWrapper<User> queryWrapper = new QueryWrapper<User>();
    queryWrapper.orderByDesc("age").orderByAsc("id");

    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);
}

③组装删除条件

@Test
public void test03(){
    //将email为null的字段进行删除
    QueryWrapper<User> queryWrapper = new QueryWrapper<User>();
    queryWrapper.isNull("email");

    //UPDATE t_user SET ready_delete=1 WHERE ready_delete=0 AND (email IS NULL)
    //因为我们有逻辑删除 所以执行删除操作时 实际上执行的是修改
    int result = userMapper.delete(queryWrapper);
    System.out.println("受影响的行数： " + result);
}

④条件的优先级

@Test
public void test04(){
    //将年龄大于18并且用户名中含有a 或 邮箱为Null的用户进行修改
    //UPDATE t_user SET age=?, email=?
    //WHERE ready_delete=0 AND (user_name LIKE ? AND age > ? OR email IS NULL)
    QueryWrapper<User> queryWrapper = new QueryWrapper<User>();
    queryWrapper.like("user_name","a")
            .gt("age",18).or().isNull("email");

    User user = new User();
    user.setAge(18);
    user.setEmail("test@qq.com");
    int update = userMapper.update(user, queryWrapper);
    System.out.println("受影响的行数:" + update);


}
@Test
public void test05(){
    //UPDATE t_user SET age=?, email=?
    // WHERE ready_delete=0 AND (user_name LIKE ? AND (age > ?) OR email IS NULL)
    QueryWrapper<User> queryWrapper = new QueryWrapper<User>();
    //lambda表达式内的逻辑 优先运算
    queryWrapper.like("user_name","a").and(i -> i.gt("age",18))
            .or().isNull("email");
    User user = new User();
    user.setAge(18);
    user.setEmail("test2@qq.com");
    int update2 = userMapper.update(user, queryWrapper);
    System.out.println("受影响的行数:" + update2);
}

⑤组装select子句

@Test
public void test06(){
    //查询用户信息username,age的字段
    //SELECT user_name,age FROM t_user WHERE ready_delete=0
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.select("user_name","age");
    //selectMaps() 返回map集合 通常配合select()使用
    //这样做的目的是避免没有被查询到的列值为null
    List<Map<String, Object>> lists = userMapper.selectMaps(queryWrapper);
    lists.forEach(System.out::println);
}

⑥子查询

@Test
public void test07(){
    //查询id小于等于5的用户  信息 (子查询实现)
    //SELECT uid AS id,user_name AS name,age,email,ready_delete FROM t_user
    // WHERE ready_delete=0 AND (uid IN (select uid from t_user where uid <=5))
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.inSql("uid","select uid from t_user where uid <=5");
    List<User> lists = userMapper.selectList(queryWrapper);
    lists.forEach(System.out::println);
}

3、UpdateWrapper使用

@Test
public void test08(){
    //将年龄大于15或邮箱为null 并且 用户名中含有a的用户信息修改
    // UPDATE t_user SET age=?,email=?
    // WHERE ready_delete=0 AND (user_name LIKE ? AND (age > ? OR email IS NULL))
    UpdateWrapper<User> updateWrapper = new UpdateWrapper<>();
    updateWrapper.set("age",18).set("email","test@qq.com").like("user_name","a")
            .and(i -> i.gt("age",15).or().isNull("email"));

    int result = userMapper.update(null, updateWrapper);
    System.out.println("result:" +result);
}

4、condition

@Test
    public void test09(){
        //模拟开发场景
        String username = "";
        Integer ageBegin = 20;
        Integer ageEnd = 30;

        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        if (StringUtils.isNotBlank(username)){
            //判断某个字符是否不为空字符串 不为null，不为空字符串
            queryWrapper.like("user_name",username);
        }
        if (ageBegin != null){
            queryWrapper.ge("age",ageBegin);
        }
        if (ageEnd != null){
            queryWrapper.le("age",ageEnd);
        }
        List<User> list = userMapper.selectList(queryWrapper);
        list.forEach(System.out::println);
    }

@Test
public void test10(){
    String username = "a";
    Integer ageBegin = 20;
    Integer ageEnd = 30;
    //使用condition条件进行组装
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.like(StringUtils.isNotBlank(username),"user_name",username)
            .ge(ageBegin != null,"age",ageBegin)
            .le(ageEnd != null,"age",ageEnd);
    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);
}

5、LambdaQueryWrapper

@Test
public void test11(){
    //定义查询条件 可能为null 用户未输入
    String username = "a";
    Integer ageBegin = 10;
    Integer ageEnd = 24;
    LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();

    //避免使用字符串表示字段 防止运行时异常
    queryWrapper.like(StringUtils.isNotBlank(username),User::getName,username)
            .ge(ageBegin != null, User::getAge,ageBegin)
            .le(ageEnd != null,User::getAge,ageEnd);

    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);
}

6、LambdaUpdateWrapper

@Test
public void test12(){
    LambdaUpdateWrapper<User> updateWrapper = new LambdaUpdateWrapper<>();
    updateWrapper.set(User::getAge,18)
            .set(User::getEmail,"test@163.com")
            .like(User::getName,"a")
            .and(i -> i.lt(User::getAge,22).or().isNull(User::getEmail));
    //lambda表达式优先运算
    User user = new User();
    int update = userMapper.update(user, updateWrapper);
    System.out.println(update);
}