MP中的lambda条件构造器

lambda条件构造器的三种创建方式

        LambdaQueryWrapper<User> lambda = new QueryWrapper<User>().lambda();
        LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();
        LambdaQueryWrapper<User> lambdaQuery = Wrappers.<User>lambdaQuery();

使用lambda条件构造器的好处：防止误写，写错后编译都通不过，语句会直接爆红。

lambda条件构造器使用案例一：

//    SELECT id,name,age,email FROM user WHERE (name LIKE ? AND age < ?) 
    @Test
    public void selectByWrapperLambda(){
//        创建lambda条件构造器的三种方式
//        LambdaQueryWrapper<User> lambda = new QueryWrapper<User>().lambda();
//        LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();
        LambdaQueryWrapper<User> lambdaQuery = Wrappers.<User>lambdaQuery();

        lambdaQuery.like(User::getName,"J").lt(User::getAge,40);

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

lambda条件构造器使用案例二：

//    SELECT id,name,age,email FROM user WHERE (name LIKE ? AND (age < ? OR email IS NOT NULL)) 
    @Test
    public void selectByWrapperLambda2(){
        LambdaQueryWrapper<User> lambdaQuery = Wrappers.<User>lambdaQuery();

        lambdaQuery.likeRight(User::getName, "J").and(lq->lq.lt(User::getAge,40).or().isNotNull(User::getEmail));

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

lambda条件构造器使用案例三：（写法与上面不同）

//    SELECT id,name,age,email FROM user WHERE (name LIKE ? AND age >= ?) 
    @Test
    public void selectByWrapperLambda3(){
        List<User> userList = new LambdaQueryChainWrapper<User>(userMapper)
                .like(User::getName, "J").ge(User::getAge, 20).list();
        
        userList.forEach(System.out::println);
    }