Data structure used for directory structure?

Question

I'm making a program which the user build directories (not in windows, in my app) and in these folders there are subfolders and so on; every folder must contain either folders or documents. What is the best data structure to use? Notice that the user may select a subfolder and search for documents in it and in its subfolders. And I don't want to limit the folders or the subfolders levels.

Answer 1

This is what I do:

Every record in the database has two fields: ID and ParentID. IDs are 4-5 characters (Base36, a-z:0-9 or something similar). Parent IDs are a concatenation of the parent's complete structure...

So...

This structure:

Root
   Folder1
   Folder2
      Folder3
   Folder4
      Folder5
         Folder6

Would be represented like this:

ID     ParentID     Name

0000   NULL           ROOT
0001   0000           Folder1
0002   0000           Folder2
0003   00000002       Folder3
0004   0000           Folder4
0005   00000004       Folder5
0006   000000040005   Folder6

I like this structure because if I need to find all the files under a folder I can do a query like:

SELECT * FROM Folders WHERE ParentID LIKE '0000%' -- to find all folders under Folder1

To delete a folder and all its children:

DELETE FROM Folders WHERE ID='0004' AND ParentID LIKE '00000004%'

To move a folder and its children, you have to update all the records that use the same parent, to the new parent.

And I don't want to linit the folders or the subfolders levels

An obvious limitation to this is that the number of subfolders are limited to the size of your ParentID field.