list构建数据库父子关系

Posted 2021-11-03 tianc.曦

list构建数据库父子关系

递归解决父子表伪代码

@Override
public List<ConsumablesDTO> getAll() {
	//数据库中获取所有的数据
    List<ConsumablesDTO> consumablesDOS = BeanUtils.deepClone(generalBeanService.queryList(new ConsumablesDO()),ConsumablesDTO.class);
    //默认根是0
    ConsumablesDTO head = new ConsumablesDTO(0);
    return getNode(consumablesDOS,head);
}

private List<ConsumablesDTO> getNode(List<ConsumablesDTO> list, ConsumablesDTO node){
    List<ConsumablesDTO> dtoList = list.stream().filter(a -> node.getId().equals(a.getParentId())).collect(Collectors.toList());
    if (CollectionUtils.isEmpty(dtoList)) return Collections.emptyList();
    dtoList.forEach(dto -> dto.setConsumablesParentDTOS(getNode(list,dto)));
    return dtoList;
}

for循环list建立树形图伪代码

public List<User> listToTree1() {
    List<User> list = list();
    List<User> tree = new ArrayList<>();
    for (User user : list) {
        //找到根节点
        if (user.getParentId() == null || user.getParentId().equals(0L)) {
            tree.add(user);
        }
        List<User> children = new ArrayList<>();
        //再次遍历list，找到user的子节点
        for (User node : list) {
            if (node.getParentId().equals(user.getId())) {
                children.add(node);
            }
        }
        user.setChildren(children);
    }
    return tree;
}

for循环list建立树形图(MAP)伪代码

//首先将获取到的List数据转换为Map集合
List userList=new ArrayList<>();
Map<String,User> map = userList.stream().collect(Collectors.toMap(User::getId,User->User));
//便利集合，进行匹配
map.forEach((k,v)->{
//如果根据pid能改查询到对应对象，证明存在父级，将该对象add进子级集合
User user = map.get(v.getPid());
if(user!=null){
user.getChildren().add(user);
}
});