PHP Tag Cloud System

Question

Hi,

I am implementing a tag cloud system based on this recommendation. (However, I am not using foreign keys)

I am allowing up to 25 tags. My question is, how can I handle editing on the items? I have this item adding/editing page:

Title: Description: Tags: (example data) computer, book, web, design

If someone edits an item details, do I need to delete all the tags from Item2Tag table first, then add the new elements? For instance, someone changed the data to this:

Tags: (example data) computer, book, web, newspaper

Do I need to delete all the tags from Item2Tag table, and then add these elements? It seems inefficient, but I could find a more efficient way.

The other problem is with this way is, if someone edits description but does not change the tags box, I still need to delete all the elements from Item2Tag table and add the same element.

I am not an experienced PHP coder, so could you suggest a better way to handle this? (pure PHP/MySQL solution is preferable)

Thanks in advance,

Answer 1

You should have a primary key on the Item2Tag table so just try and insert the links to the new tags - this will however error out if an item2tag link already exists. Depending on the DBMS you are using there are different ways of handling this. MySQL provides the following syntax:

INSERT INTO table (a,b,c) VALUES (1,2,3)
  ON DUPLICATE KEY UPDATE c=c+1;

Which is equivalent to:

UPDATE table SET c=c+1 WHERE a=1;

If the record already exists.

For your second problem, well you shouldn't need to alter the tags if the item_id of the item is not changed. The Item2Tag table links an item to a tag, but if item_id remains constant there is no need to alter the tags.

Answer 2

In your system you already know the current tags, so what you can do is make a delta.

To use your own example, these are the starting tags: computer, book, web, design

And someone changes this too: computer, book, web, newspaper

// Quick & dirty example (pseudo)code
$current_tags = array('computer', 'book', 'web', 'design');
$new_tags = array('computer', 'book', 'web', 'newspaper');

foreach ($new_tags as $key => $new_tag) {
  if (!in_array($new_tag, $current_tags) {
    $tags_to_add[] = $new_tag;
  } else {
    // Delete item from $current_tags
  }
}
// Now delete the items left in $current_tags
// And then add the items in $tags_to_add