MyBatis-Plus 进阶之 lambda 编程

刺骨的言语ヽ痛彻心扉 2023-01-16 03:21 133阅读 0赞

## QueryWrapper ##

public void select1(){ 
        QueryWrapper<User> qw = new QueryWrapper<>();
        qw.select("id","name","nickname");
        List<User> users = userMapper.selectList(qw);
        users.forEach(System.out::println);
    }
    
    public void select2(){ 
        QueryWrapper<User> qw = new QueryWrapper<>();
        qw.select(User.class,i -> i.getColumn().equals("name"));//查询name
        // qw.select(User.class,i -> !i.getColumn().equals("nickname")); //排除nickname
        List<User> users = userMapper.selectList(qw);
        users.forEach(System.out::println);
    }

## UpdateWrapper ##

public void set(){ 
        UpdateWrapper<User> uw = new UpdateWrapper<>();
        uw.set("gender",false)
                .in("id",1,3,5);
        int res = userMapper.update(null, uw);
        System.out.println(res);
    }
    
    public void setSQL(){ 
        UpdateWrapper<User> uw = Wrappers.update();
        uw.setSql("password=4321"); // UPDATE tb_user SET password=4321;
        int res = userMapper.update(null, uw);
        System.out.println(res);
    }

## QueryWrapper \# lambda ##

public void between(){ 
        QueryWrapper<User> qw = Wrappers.query();
        qw.lambda().between(User::getId,10,20);
        List<User> users = userMapper.selectList(qw);
        users.forEach(System.out::println);
    }
    
    public void delete(){ 
        QueryWrapper<User> qw = Wrappers.query();
        qw.lambda().eq(User::getId,30);
        int res = userMapper.delete(qw);
    }
    
    public void update(){ 
        UpdateWrapper<User> uw = Wrappers.update();
        uw.lambda().eq(User::getId,30).setSql("name='张三四'");
        int res = userMapper.update(null, uw);
        System.out.println(res);
    }
    
    public void count(){ 
        QueryWrapper<User> qw = Wrappers.query();
        qw.lambda().like(User::getNickname,"an");
        Integer res = userMapper.selectCount(qw);
        System.out.println(res);
    }

## LambdaQueryWrapper ##

public void eqDemo() { 
        //使用 QueryWrapper 的成员方法方法 lambda 构建 LambdaQueryWrapper
        LambdaQueryWrapper<User> lqw = new QueryWrapper<User>().lambda();
        lqw.eq(User::getId, 2);
        User user = userMapper.selectOne(lqw);
        System.out.println(user);
    }
    
    public void inDemo() { 
        //直接 new 出 LambdaQueryWrapper
        LambdaQueryWrapper<User> lqw = new LambdaQueryWrapper<>();
        lqw.in(User::getId, 1, 2, 3);
        List<User> users = userMapper.selectList(lqw);
        users.forEach(System.out::println);
    }
    
    public void likeDemo() { 
        //使用 Wrappers 的静态方法 lambdaQuery 构建 LambdaQueryWrapper（推荐）
        LambdaQueryWrapper<User> lqw = Wrappers.lambdaQuery();
        lqw.like(User::getUsername, "an");
        List<User> users = userMapper.selectList(lqw);
        users.forEach(System.out::println);
    }
    
    public void oneDemo() { 
        //使用 链式查询 的方法构建 LambdaQueryWrapper
        User user = new LambdaQueryChainWrapper<User>(userMapper)
                .eq(User::getId, 10)
                .one();
        System.out.println(user);
    }
    
    public void likeRightDemo() { 
        //使用 链式查询 的方法构建 LambdaQueryWrapper
        List<User> users = new LambdaQueryChainWrapper<User>(userMapper)
                //相当于原生 sql 的 like 右通配符模糊查询，比如：like 'an%'
                .likeRight(User::getUsername, "an")
                .list();
        users.forEach(System.out::println);
    }
    
    public void likeLeftDemo() { 
        LambdaQueryWrapper<User> lqw = Wrappers.lambdaQuery();
        //相当于原生 sql 的 like 右通配符模糊查询，比如：like '%an'
        lqw.likeLeft(User::getUsername, "an");
        List<User> users = userMapper.selectList(lqw);
        users.forEach(System.out::println);
    }
    
    public void partColumnsDemo() { 
        LambdaQueryWrapper<User> lqw = Wrappers.lambdaQuery();
        //查询指定的字段
        lqw.select(User::getId, User::getName, User::getNickname)
                .eq(User::getUsername, "an");
        List<User> users = userMapper.selectList(lqw);
        users.forEach(System.out::println);
    }
    
    public void ifDemo() { 
        User condition = User.builder().username("zhangsan").build();
        LambdaQueryWrapper<User> lqw = Wrappers.lambdaQuery();
        lqw.eq(condition.getGender() != null, User::getGender, condition.getGender())
                .eq(condition.getUsername() != null, User::getUsername, condition.getUsername());
        List<User> users = userMapper.selectList(lqw);
        users.forEach(System.out::println);
    }
    
    public void orAndDemo() { 
        LambdaQueryWrapper<User> lqw = Wrappers.lambdaQuery();
        lqw.gt(User::getCredit, 10000)
                .and(wrapper -> wrapper.lt(User::getCredit, 100000))
                .or()
                .eq(User::getGender, true);
        List<User> users = userMapper.selectList(lqw);
        users.forEach(System.out::println);
    }
    
    public void pageDemo() { 
        Page<User> page = new Page<>(4, 3);
        LambdaQueryWrapper<User> lqw = Wrappers.lambdaQuery();
        lqw.orderByAsc(User::getId);
        Page<User> res = userMapper.selectPage(page, lqw);
        res.getRecords().forEach(System.out::println);
    }
    
    public void updateDemo1() { 
        LambdaUpdateWrapper<User> luw = Wrappers.lambdaUpdate();
        luw.eq(User::getId, 5)
                .set(User::getName, "大中国")
                .set(User::getUsername, "老大");
        userMapper.update(null, luw);
    }
    
    public void updateDemo2() { 
        LambdaUpdateWrapper<User> luw = new LambdaUpdateWrapper<>();
        luw.eq(User::getId, 3)
                .set(User::getNickname, "wanger");
        int res = userMapper.update(null, luw);
        System.out.println(res);
    }
    
    public void updateDemo3() { 
        boolean res = new LambdaUpdateChainWrapper<User>(userMapper)
                .eq(User::getId, 4)
                .set(User::getNickname, "mazi")
                .update();
        System.out.println(res);
    }