PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

758 Chapter 31 Building Web Forums
The most important thing that happens in this constructor is that the child nodes of
this node are instantiated.You begin this process by checking whether you need to
expand the child nodes.You perform this process only if a node has some children, and
you have elected to display them:
if(($sublist||$expand) && $children){
$conn = db_connect();
You then connect to the database and retrieve all the child posts, as follows:
$query = "select * from header where parent = '".$postid."' order by posted";
$result = $conn->query($query);
Next, you fill the array $m_childlist with instances of the treenode class, containing
the replies to the post stored in this treenode, as follows:
for ($count=0; $row = @$result->fetch_assoc(); $count++) {
if($sublist || $expanded[$row['postid']] == true) {
$expand = true;
} else {
$expand = false;
}
$this->m_childlist[$count]= new treenode($row['postid'],$row['title'],
$row['poster'],$row['posted'], $row['children'], $expand,
$depth+1, $expanded, $sublist);
}
This last line creates the new treenodes, following exactly the same process we just
walked through, but for the next level down the tree.This is the recursive part: A parent
tree node calls the treenode constructor, passes its own postid as parent, and adds one
to its own depth before passing it.
Each treenode, in turn, is created and then creates its own children until you run out
of replies or levels that you want to expand to.
After all that’s done, you call the root treenode’s display function (back in
display_tree()), as follows:
$tree->display($row, $sublist);
The display() function begins by checking whether this is the dummy root node:
if($this->m_depth > -1)
In this way, the dummy can be left out of the display.You don’t want to completely skip
the root node, though.You do not want it to appear, but it needs to notify its children
that they need to display themselves.
The display() function then starts drawing the table containing the articles. It uses
the modulus operator (%) to decide what color background this row should have (hence
they alternate):