Question

我想将磁盘上存在的目录存储到数据库中，同时维护它们的层次结构/树结构。

这是一个无花果，

                         (ROOT)
                       /        \ 
                    Dir2        Dir3
                   /    \           \
                 Dir4   Dir5        Dir6
                 /          
               Dir7

我正在使用 SQLite 数据库。

请建议我在SQLite数据库中存储上述结构的sql查询。
以及在我选择目录时检索目录的完整路径的查询。

即。假设我选择了Dir6然后我会得到完整的路径，如ROOT / Dir2 / dir3 / dir7

Answer 1

这是SQLite的快速闭包表示例。我没有包含将项目插入现有树的语句。相反，我刚刚手动创建了语句。您可以在Models for hierarchical data幻灯片中找到插入和删除语句。

为了我在插入目录的ID时的理智，我重命名了目录以匹配他们的ID：

        (ROOT)
      /        \ 
    Dir2        Dir3
    /    \           \
  Dir4   Dir5        Dir6
  /          
Dir7

创建表格

CREATE TABLE `filesystem` (
  `id` INTEGER,
  `dirname` TEXT,
  PRIMARY KEY (`id`)
);

CREATE TABLE `tree_path` (
  `ancestor` INTEGER,
  `descendant` INTEGER,
  PRIMARY KEY (`ancestor`, `descendant`)
);

将目录插入filesystem表格

INSERT INTO filesystem (id, dirname) VALUES (1, 'ROOT');
INSERT INTO filesystem (id, dirname) VALUES (2, 'Dir2');
INSERT INTO filesystem (id, dirname) VALUES (3, 'Dir3');
INSERT INTO filesystem (id, dirname) VALUES (4, 'Dir4');
INSERT INTO filesystem (id, dirname) VALUES (5, 'Dir5');
INSERT INTO filesystem (id, dirname) VALUES (6, 'Dir6');
INSERT INTO filesystem (id, dirname) VALUES (7, 'Dir7');

创建闭包表路径

INSERT INTO tree_path (ancestor, descendant) VALUES (1, 1);
INSERT INTO tree_path (ancestor, descendant) VALUES (1, 2);
INSERT INTO tree_path (ancestor, descendant) VALUES (1, 3);
INSERT INTO tree_path (ancestor, descendant) VALUES (1, 4);
INSERT INTO tree_path (ancestor, descendant) VALUES (1, 5);
INSERT INTO tree_path (ancestor, descendant) VALUES (1, 6);
INSERT INTO tree_path (ancestor, descendant) VALUES (1, 7);
INSERT INTO tree_path (ancestor, descendant) VALUES (2, 2);
INSERT INTO tree_path (ancestor, descendant) VALUES (2, 4);
INSERT INTO tree_path (ancestor, descendant) VALUES (2, 5);
INSERT INTO tree_path (ancestor, descendant) VALUES (2, 7);
INSERT INTO tree_path (ancestor, descendant) VALUES (3, 3);
INSERT INTO tree_path (ancestor, descendant) VALUES (3, 6);
INSERT INTO tree_path (ancestor, descendant) VALUES (4, 4);
INSERT INTO tree_path (ancestor, descendant) VALUES (4, 7);
INSERT INTO tree_path (ancestor, descendant) VALUES (5, 5);
INSERT INTO tree_path (ancestor, descendant) VALUES (6, 6);
INSERT INTO tree_path (ancestor, descendant) VALUES (7, 7);

运行一些查询

# (ROOT) and subdirectories
SELECT f.id, f.dirname FROM filesystem f
  JOIN tree_path t
    ON t.descendant = f.id
 WHERE t.ancestor = 1;

+----+---------+
| id | dirname |
+----+---------+
|  1 | ROOT    |
|  2 | Dir2    |
|  3 | Dir3    |
|  4 | Dir4    |
|  5 | Dir5    |
|  6 | Dir6    |
|  7 | Dir7    |
+----+---------+


# Dir3 and subdirectories
SELECT f.id, f.dirname
  FROM filesystem f
  JOIN tree_path t
    ON t.descendant = f.id
 WHERE t.ancestor = 3;

+----+---------+
| id | dirname |
+----+---------+
|  3 | Dir3    |
|  6 | Dir6    |
+----+---------+

# Dir5 and parent directories
SELECT f.id, f.dirname
  FROM filesystem f
  JOIN tree_path t
    ON t.ancestor = f.id
 WHERE t.descendant = 5;

+----+---------+
| id | dirname |
+----+---------+
|  1 | ROOT    |
|  2 | Dir2    |
|  5 | Dir5    |
+----+---------+

# Dir7 and parent directories
SELECT f.id, f.dirname
  FROM filesystem f
  JOIN tree_path t
    ON t.ancestor = f.id
 WHERE t.descendant = 7;

+----+---------+
| id | dirname |
+----+---------+
|  1 | ROOT    |
|  2 | Dir2    |
|  4 | Dir4    |
|  7 | Dir7    |
+----+---------+

SELECT f.id, f.dirname
  FROM filesystem f
  JOIN tree_path t
    ON t.ancestor = f.id
 WHERE t.descendant = (
SELECT id
  FROM filesystem
 WHERE dirname LIKE '%7%'
);

+----+---------+
| id | dirname |
+----+---------+
|  1 | ROOT    |
|  2 | Dir2    |
|  4 | Dir4    |
|  7 | Dir7    |
+----+---------+

Answer 2

您将分层数据表示为一系列节点，每个节点都有一个ID和一个父ID。您可以将您存储在名为DIRTAB的表中，该表包含2个ID列，另一个表用于单个目录名的文本：

ID -- as a primary key  
PARENT_ID -- refers to the ID of the parent row in DIRTAB  
DIRNAME -- the text of the name eg Dir5

SQLite缺少Oracle必须处理分层数据的CONNECT BY子句，但我认为如果你准备接受一些丑陋的SQL，你可以近似分层的东西：

SELECT (CASE WHEN p5.DIRNAME IS NOT NULL THEN p5.DIRNAME || '/' ELSE '' END) ||
       (CASE WHEN p4.DIRNAME IS NOT NULL THEN p4.DIRNAME || '/' ELSE '' END) ||
       (CASE WHEN p3.DIRNAME IS NOT NULL THEN p3.DIRNAME || '/' ELSE '' END) ||
       (CASE WHEN p2.DIRNAME IS NOT NULL THEN p2.DIRNAME || '/' ELSE '' END) ||
       (CASE WHEN p1.DIRNAME IS NOT NULL THEN p1.DIRNAME || '/' ELSE '' END) ||
       p0.DIRNAME as FULLPATH
FROM DIRTAB p0
     LEFT OUTER JOIN DIRTAB p1 ON p1.ID = p0.PARENT_ID
     LEFT OUTER JOIN DIRTAB p2 ON p2.ID = p1.PARENT_ID
     LEFT OUTER JOIN DIRTAB p3 ON p3.ID = p2.PARENT_ID
     LEFT OUTER JOIN DIRTAB p4 ON p4.ID = p3.PARENT_ID
     LEFT OUTER JOIN DIRTAB p5 ON p5.ID = p4.PARENT_ID
WHERE p0.DIRNAME = 'Dir6'

这里的问题是您必须预测目录结构的最大深度并扩展SQL语句以应对。我做了6个级别作为例子另外我假设SQLite连接空字符串没有问题。（某些DB将它们视为null并将整个表达式结果转换为null）

Answer 3

我认为您应该阅读有关修改预订树遍历的方法：http://www.sitepoint.com/hierarchical-data-database/

该链接讨论了将分层数据存储到关系数据库中的两种方法：邻接列表模型和修改后的预订树遍历算法。

修改预订树遍历方法的主要思想是使用指向辅助导航和子树选择的所有节点注释：

文件系统中目录的分层/树数据库

3 个答案: