PHP: Rotating through an array

Question

I've got a website on which I want to display items. These items are stored in a database in the following format:

ID  Item    Active
1   My item 0
2   My item 1
7   My item 1
8   My item 1
10  My item 0

Note here that the IDs are not necessarily evenly spaced. Each item is either active(1) or inactive(0). I want 3 items to be active at a time and every time my script is called I want the next item to become active and the oldest item to become inactive like so:

ID  Item    Active
1   My item 0
2   My item 0
7   My item 1
8   My item 1
10  My item 1

and so:

ID  Item    Active
1   My item 1
2   My item 0
7   My item 0
8   My item 1
10  My item 1

I'm currently struggling with the algorithm to consider the third case above. I can't just pick the highest ID that's active and move to the next item and set that active and at the same time pick the lowest one that's active and make it inactive.

Here's my code so far:

{
            for ($i=0;$i<sizeof($videos);$i++)
        {
            echo $i."]";
            
            if ($videos[$i]->active == 1)
            {
                if (!isset($first_active))
                {
                    echo "mooh";
                    echo "[";
                    echo $first_active = $i;
                    echo "]";
                }
                
                if ( ($i < (sizeof($videos)-1)) && ($videos[$i+1]->active == 0) )
                {
                    $videos[$i+1]->active = 1;
                    $videos[$i+1]->update();
                    
                    echo "@".$first_active."|".$videos[$first_active]->id()."@";
                    $videos[$first_active]->active = 0;
                    $videos[$first_active]->update();
                    
                    $first_active = null;
                    
                    echo "|".$videos[$i+1]->id();
                    break;
                }
                elseif ($i == (sizeof($videos)-1))
                {
                    $videos[0]->active = 1;
                    $videos[0]->update();
                    
                    $videos[$first_active]->active = 0;
                    $videos[$first_active]->update();
                    
                    $first_active = null;
                    
                    echo "|".$videos[0]->id();
                    break;
                }
            }
        }
    }

This works until I get to the end, e.g. ID 10. It then correctly makes ID 1 active. In the next call, it makes ID 7 active and ID 1 inactive.

Any idea how I can 1) fix my code, 2) tackle this problem smarter?

Lochemage · Accepted Answer · 2013-09-20 20:21:06Z

2

Sounds to me like you actually need to store the last activation date instead of a simple on/off flag.

You can use two database queries, one to get the full list in order of ID, and another that specifically only gets the first 3 entries sorted by active date. Loop through your full list to get all the entries in order, then test the ID of each one with the ID of your 3 active to test if it is currently active. Then, setting a new item active is as simple as just updating the date/time of the active column on the item you want.

If you really want to keep the active on/off flag, then do so, just make another column with a last active date/time.

answered Sep 20, 2013 at 20:21

Lochemage

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2 Comments

Todd Holmberg Over a year ago

I like this approach. Keep the active flag if you want, but adding a last_activated column would be useful in your use case, as well as in other time-based query situations.

Jan K. Over a year ago

Thanks, this worked wonderfully. I kept the active flag and added an activation (timestamp) column. Two queries allow me to activate and deactivate a record. Essentially: get first where active = 0 sort by activation time asc id asc get first where active = 1 sort by activation time asc id asc

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