在postgres数据库中保存文件树的最简单方法是什么?

时间:2013-11-07 11:10:22

标签: postgresql database-design

我正在从dropbox api中检索文件树。在api中,每个文件夹都使用单独的api调用来读取,因此我将遍历整个文件树以获取所有文件夹。这是通过cron-job完成的。

从dropbox检索数据的函数如下所示:

function renderFolderTree($myobject, $path){
    $entry = $myobject->getMetadataWithChildren($path);
    foreach ($entry['contents'] as $child) {
        if ($child['is_dir']){
            $folderpath = $child['path'];
            //this will retrieve the child-folder
            renderFolderTree($myobject, $folderpath, $filetree);
            //here I need something that saves the folder
        }else{
            print_r($child);
            //here I need something that saves the file
        }
    }
}

我想将文件树保存到postgres数据库,以便以后可以将其作为代表它的json对象输出。

我是数据库设计的新手,不知道保存数据的方法。我假设每个文件和文件夹都应该有自己的数据库条目。我可以让每个孩子都引用它的父母ID,或者我可以让每个父母都包含它的孩子列表。

我是新手,我想要一个相当简单的解决方案,阅读速度比写作更重要!

1 个答案:

答案 0 :(得分:5)

在关系数据库中存储树有几种选择。 为了更好地概述,我推荐Bill Karwin的slides

由于您提到读取速度最重要,因此闭包表将是一种适当的强大编码。闭包表是多对多关系,其为每个路径(例如,/ a / b / c)存储所有父/子(传递)。这样,可以使用一个SQL查询(非递归)完成对树的许多查询。

那看起来像

create table nodes (
    path varchar primary key
    /* your other attributes here, can be null */
);

create table parents_children (
    parent_path varchar,
    child_path varchar,
    primary key(parent_path,child_path),
    foreign key (parent_path) references nodes (path),
    foreign key (child_path) references nodes (path)
);

要在目录/ a / b /下插入新文件/ a / b / c,您可以这样做:

insert into nodes values ('/a/b/c');

insert into parents_children
select parent_path, '/a/b/c' from parents_children where child_path = '/a/b/'
union all select '/a/b/c','/a/b/c';

例如,查询来自' / a'的所有儿童。在递归上,你会这样做:

select * 
from nodes join parents_children on path = child_path
where parent_path = '/a';

更详尽的示例,它存储以下文件树:

/
/a/
/a/b/
/a/b/d
/a/c
/b

要插入数据:

insert into nodes values ('/');
insert into parents_children values ('/','/');

insert into nodes values ('/a/');
insert into parents_children
select parent_path, '/a/' from parents_children where child_path = '/'
union all select '/a/','/a/';

insert into nodes values ('/a/b/');
insert into parents_children
select parent_path, '/a/b/' from parents_children where child_path = '/a/'
union all select '/a/b/','/a/b/';

insert into nodes values ('/a/c');
insert into parents_children
select parent_path, '/a/c' from parents_children where child_path = '/a/'
union all select '/a/c','/a/c';

insert into nodes values ('/a/b/d');
insert into parents_children
select parent_path, '/a/b/d' from parents_children where child_path = '/a/b/'
union all select '/a/b/d','/a/b/d';

insert into nodes values ('/b');
insert into parents_children
select parent_path, '/b' from parents_children where child_path = '/'
union all select '/b','/b';

查询/ a /

的所有子项
select node.*
from nodes join parents_children on path = child_path
where parent_path = '/a/';

path        
----------  
/a/         
/a/b/       
/a/b/d      
/a/c