Help! BBS Script making me go nuts!!!

Anon

If anyone has read the book "Core PHP programming" you'll notice it has a BBS script near the end of the book. It's totally confusing me, here's what it looks like:

     Simple BBS system using MySQL.  Make the following 
     table:

            CREATE TABLE bbsMessage
            (
                    ID INT NOT NULL AUTO_INCREMENT,
                    Title VARCHAR(64),
                    Poster VARCHAR(64),
                    Created DATETIME,
                    Parent INT,  
                    Body BLOB,
                    PRIMARY KEY(ID)
            );

    *******************************************************/

    printf("<H1>Leon's BBS</H1>\n");

    /* set up database */
    mysql_pconnect("www.yoursever.com", "httpd");
    $Database = "yourdb";

    /****************************************************************
     recursive function that spits out all descendent messages
    ****************************************************************/
    function showMessages($parentID)   
    {
            global $Database;

            $dateToUse = Date("U");

            echo "<UL>\n";

            /* show all the wings */                
            $Query = "SELECT * FROM bbsMessage ";
            $Query = $Query . "WHERE Parent=$parentID ";

            $Query = $Query . "ORDER BY Created ";

            $result = mysql($Database,$Query);
            $numRows = mysql_NumRows($result);
            $RowCount = 0;
            while($RowCount < $numRows)
            {
                    $messageID = mysql_result($result,$RowCount,"ID");
                    $messageTitle = mysql_result($result,$RowCount,"Title");
                    $messageCreated = mysql_result($result,$RowCount,"Created");
                    $messageParent = mysql_result($result,$RowCount,"Parent");

                    /* put a line telling what the wing is */       
                    printf("<LI>($messageCreated) <A HREF=\"bbs.htma?messageID=$messageID\">$messageTitle</A><BR>\n");

!!! Assuming that ParentID was equal to 4, this would print the first result it finds in
!!! the query, correct? And the first one is the parent correct? What is parent supposed to equal anyway?

                    /* call getWingContents to get this branch */
                    showMessages($messageID);

!!! I'm lost here.. the $messageID is equal to the auto_incrementing ID in the database,
!!! right? And aren't you calling the same function that we are creating right now?
!!! I didn't know that was possible. I don't understand how using the auto_increment ID
!!! will show the children. Basically i'm totally confused, I would appreciate it if you
!!! could somehow explain how this works in detail, or in somewhat easier terms.

                    $RowCount++;
            }

            echo "</UL>\n";
    }

    /****************************************************************
     print out a form for adding a message with parent id given
    ****************************************************************/
    function postForm($parentID, $useTitle)
    {
            printf("<FORM ACTION=\"bbs.htma\" METHOD=\"post\">\n");
            printf("<INPUT TYPE=\"hidden\" NAME=\"inputParent\" VALUE=\"$parentID\">");
            printf("<INPUT TYPE=\"hidden\" NAME=\"ACTION\" VALUE=\"POST\">");
            printf("<TABLE BORDER=\"1\" CELLSPACING=\"0\" CELLPADDING=\"5\" WIDTH=\"400\">\n");
            printf("<TR><TD WIDTH=\"100\"><B>Title</B></TD>");
            printf("<TD WIDTH=\"300\"><INPUT TYPE=\"text\" NAME=\"inputTitle\" SIZE=\"35\" MAXLENGTH\"64\" VALUE=\"$useTitle\"></TD></TR>\n");
            printf("<TR><TD WIDTH=\"100\"><B>Poster</B></TD>");
            printf("<TD WIDTH=\"300\"><INPUT TYPE=\"text\" NAME=\"inputPoster\" SIZE=\"35\" MAXLENGTH\"64\"></TD></TR>\n");
            printf("<TR><TD COLSPAN=\"2\" WIDTH=\"400\">");
            printf("<TEXTAREA NAME=\"inputBody\" COLS=\"45\" ROWS=\"5\"></TEXTAREA></TD></TR>\n");
            printf("<TR><TD COLSPAN=\"2\" WIDTH=\"400\"><CENTER><INPUT TYPE=\"submit\" VALUE=\"Post\"></CENTER></TD></TR>\n");
            printf("</TABLE>\n");
            printf("</FORM>\n");

    }

    /******************************************************
     perform actions
    ******************************************************/
    if($ACTION != "")
    {
            if($ACTION == "POST")
            {
                    $inputTitle = ereg_replace("'", "''", $inputTitle);
                    $inputBody = ereg_replace("'", "''", $inputBody);

                    $Query = "INSERT INTO bbsMessage ";
                    $Query .= "VALUES(0, '$inputTitle', ";
                    $Query .= "'$inputPoster', ";
                    $Query .= "now(), $inputParent, ";
                    $Query .= "'$inputBody')";

                    $result = mysql($Database,$Query);


            }

    }


    /******************************************************
     Show Message or show list of messages
    ******************************************************/
    if($messageID > 0)
    {
            $Query = "SELECT * FROM bbsMessage ";
            $Query = $Query . "WHERE ID=$messageID ";

            $result = mysql($Database,$Query);
            $numRows = mysql_NumRows($result);
            $RowCount = 0;
            if($RowCount < $numRows)
            {
                    $messageID = mysql_result($result,$RowCount,"ID");
                    $messageTitle = mysql_result($result,$RowCount,"Title");
                    $messagePoster = mysql_result($result,$RowCount,"Poster");
                    $messageCreated = mysql_result($result,$RowCount,"Created");
                    $messageParent = mysql_result($result,$RowCount,"Parent");
                    $messageBody = mysql_result($result,$RowCount,"Body");

                    printf("<TABLE BORDER=\"1\" CELLSPACING=\"0\" CELLPADDING=\"5\" WIDTH=\"400\">\n");
                    printf("<TR><TD WIDTH=\"100\"><B>Title</B></TD><TD WIDTH=\"300\">$messageTitle</TD></TR>\n");
                    printf("<TR><TD WIDTH=\"100\"><B>Poster</B></TD><TD WIDTH=\"300\">$messagePoster</TD></TR>\n");
                    printf("<TR><TD WIDTH=\"100\"><B>Posted</B></TD><TD WIDTH=\"300\">$messageCreated</TD></TR>\n");
                    printf("<TR><TD COLSPAN=\"2\" WIDTH=\"400\">$messageBody</TD></TR>\n");
                    printf("</TABLE>\n");

                    postForm($messageID, "RE: $messageTitle");

            }


            echo "<A HREF=\"bbs.htma\">List of Messages</A><BR>";

    }
    else
    {
            printf("<H2>List of Messages</H2>\n");

            /* call recursive function */
            showMessages(0);

            postForm(0, "");

    }

</BODY>

Anon

So do you have a question about this?

Anon

Yes if you read the script you would see that I put comments in areas which I don't understand. They are like this"!!! Comments here". What I don't understand is how this script is able to display the messages, and how it makes branched display.

Anon

Sorry I was just skimming when I originally read your message.

First off this is a basic threaded messaging system. The MessageID is a unique identifier marking each entry into the database. The ParentID is going to match an already created MessageID so that messages can be displayed in a threaded enviroment. And yes it is possible to call a function recrusively (calling it from itself), it's dangerous if you don't know what you are doing cause you can get into an infinate loop.

So using this message as an example, you posted a message which got put into the database with a MessageID of 1 and a ParentID of 0 (marking it as the root message), when I responded I got a MessageID of 2 and a ParentID of 1, your second message to me got a MessageID of 3 and a ParentID of 2, and this message will get a MessageID of 4 and a ParentID of 3. Now if someone eles responded to your first message they would get a MessageID of 5 and a ParentID of 1. This is how threaded messaging works. The first message has no parent so you know where you are starting.

If you look at the bottom of the code the first thing it does it see if the user has selected a message to view, if not it calls the showMessages function and passes it a 0, which is telling it to list all messages that are parents. The showMessages function selects all messages with a ParentID of 0, and for each one it displays some information and then calls showMessages with that messages MessageID to see if there are any children. If it encounters any children it looks to see if that message has any childern, it will keep doing this until it get's to a message without any children, and then it will back up a step and move to the next message.

Let me know if this helps, or if you have other questions.

Anon

I just decided to write a threaded msg system using PHP/SQL and I've been racking my brains trying to think how the threaded system works.. RECURSION! Why I didn't think of it before, I'm slapping my head now repeatedly.

Thank you!

Anon

This is a test post, don't read anything into this please 🙂