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Thread: Storing and retrieving directory structures in MYSQL

  1. #1
    Join Date
    Oct 2009
    Posts
    77

    Question Storing and retrieving directory structures in MYSQL

    Has anyone here created some sort of directory structure before, with categories & subcategories, that they stored in a mysql database?

    This first time I tried this, I set up each record with a category name, category id and parent id (The parent id for root-level categories was 0). I figured there was some sort of recursive function that would retrieve the tree structure from the database. However, I just couldn't figure it out. In the end I settled on a different solution.

    I stored my category records like this:

    Code:
    Category Name       Order         Level
    
    Category A              1             0
    Category AB             2             1
    Category B              3             0
    Category BA             4             1
    Category BAA            5             2
    The fields were printed out by their order number ascending, and indented based on their level number like this:

    Code:
    Category A
    |_Category AB
    |
    Category B
    |_Category BA
      |_Category BAA
    From this could be inferred the parent-child relationships between categories. But now the order numbers have to be refreshed every time a category is added or deleted, which is more error-prone than just storing the parent-child relationships.

    Can anyone else share how they store and retrieve directory structures?

  2. #2
    Join Date
    Dec 2005
    Posts
    2,984
    EDIT: Whoops...did it for just one level deep....
    Last edited by aj_nsc; 05-14-2011 at 06:47 PM.
    I've switched careers...
    I'm NO LONGER a scientist,
    but now a web developer...
    awesome.

  3. #3
    Join Date
    Dec 2005
    Posts
    2,984
    I WIN!!!! (me being excited because I finally figured it out)

    Your first instinct was correct, you only need an id, name, and parentID.

    Here is the solution:

    Code:
    ID     Name              ParentID
    1      CategoryA          0
    2      CategoryAA         1
    3      CategoryAAA       2
    4      CategoryAAB       2
    5      CategoryB           0
    6      CategoryBA         5
    7      CategoryBB         5
    8      CategoryBAA       6
    9      CategoryBAAA     7
    There's a couple of tricks here:

    1) You have to order them ascending by ParentID so you can loop through them the right way

    2) The & symbol indicates pass by reference in the below function:

    PHP Code:
    $organizedTree = array();

    $sql mysql_query("select * from `categories` order by ParentID asc");
    while(
    $row mysql_fetch_assoc($sql)) {
     
    $row['children'] = array();
     if((bool)
    $row['ParentID']) {
      
    addToTree($organizedTree,$row['ParentID'],$row);
     } else {
      
    $organizedTree[$row['ID']] = $row;
     }   
    }

    function 
    addToTree(&$parentTree,$pid,$category) {
     foreach(
    $parentTree as $parentID => $parentCategory) {
      if(
    $parentID == $pid) {
       return 
    $parentTree[$parentID]['children'][$category['id']] = $category;
      } else {
       
    addToTree($parentTree[$parentID]['children'],$pid,$category);
      }
     }
    }

    print_r($organizedTree); 
    Last edited by aj_nsc; 05-14-2011 at 08:15 PM.
    I've switched careers...
    I'm NO LONGER a scientist,
    but now a web developer...
    awesome.

  4. #4
    Join Date
    Oct 2009
    Posts
    77

    Question

    Thanks, aj.

  5. #5
    Join Date
    Dec 2005
    Posts
    2,984
    Come on? Just a thanks? I consider this a work of art!

    (Sorry, I'm a huge nerd - I should actually be thanking you for letting me add such a cool block of code to my own library!)

    P.S. Glad I could help.
    I've switched careers...
    I'm NO LONGER a scientist,
    but now a web developer...
    awesome.

  6. #6
    Join Date
    Oct 2009
    Posts
    77
    lol, no problem, I'm a nerd too. Have fun!

  7. #7
    Join Date
    Sep 2012
    Posts
    2
    hello very nice..can you send me this code for c#..i need same functionality wat u written above

  8. #8
    Join Date
    Jul 2013
    Posts
    1
    dear, I am also having the same problem, but can't get your solution

    what does it mean by: $row['children'] and $category['id']

    are they database (table) column ???

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