简述论坛中无限分类的实现原理

<?php
/*
数据表结构如下:
CREATE TABLE `category` (
`categoryID` smallint(5) unsigned NOT NULL auto_increment,
`categoryParentID` smallint(5) unsigned NOT NULL default ‘0’,
`categoryName` varchar(50) NOT NULL default ”,
PRIMARY KEY (`categoryID`)
) ENGINE=MyISAM DEFAULT CHARSET=gbk;
INSERT INTO `category` ( `categoryParentID`, `categoryName`) VALUES
(0, ‘一级类别’),
(1, ‘二级类别’),
(1, ‘二级类别’),
(1, ‘二级类别’),
(2, ‘三级类别’),
(2, ‘333332’),
(2, ‘234234’),
(3, ‘aqqqqqd’),
(4, ‘哈哈’),
(5, ‘66333666’);
*/
//指定分类id变量$category_id,然后返回该分类的所有子类
//$default_category为默认的选中的分类
function Get_Category($category_id = 0,$level = 0, $default_category = 0)
{
global $DB;
$sql = “SELECT * FROM category ORDER BY categoryID DESC”;
$result = $DB->query( $sql );
while ($rows = $DB->fetch_array($result))
{
$category_array[$rows[categoryParentID]][$rows[categoryID]] = array(‘id’ => $rows

[categoryID], ‘parent’ => $rows[categoryParentID], ‘name’ => $rows
[categoryName]);
}
if (!isset($category_array[$category_id]))
{
return “”;
}
foreach($category_array[$category_id] AS $key => $category)
{
if ($category[‘id’] == $default_category)
{
echo “<option selected value=”.$category[‘id’].””;
}else
{
echo “<option value=”.$category[‘id’].””;
}
if ($level > 0)
{
echo “>” . str_repeat( ” “, $level ) . ” ” . $category[‘name’] . “</option>n”;
}
else
{
echo “>” . $category[‘name’] . “</option>n”;
}
Get_Category($key, $level + 1, $default_category);
}
unset($category_array[$category_id]);
}
/*
函数返回的数组格式如下所示:
Array
(
[1] => Array ( [id] => 1 [name] => 一级类别 [level] => 0 [ParentID] => 0 )
[4] => Array ( [id] => 4 [name] => 二级类别 [level] => 1 [ParentID] => 1 )
[9] => Array ( [id] => 9 [name] => 哈哈 [level] => 2 [ParentID] => 4 )
[3] => Array ( [id] => 3 [name] => 二级类别 [level] => 1 [ParentID] => 1 )
[8] => Array ( [id] => 8 [name] => aqqqqqd [level] => 2 [ParentID] => 3 )
[2] => Array ( [id] => 2 [name] => 二级类别 [level] => 1 [ParentID] => 1 )
[7] => Array ( [id] => 7 [name] => 234234 [level] => 2 [ParentID] => 2 )
[6] => Array ( [id] => 6 [name] => 333332 [level] => 2 [ParentID] => 2 )
[5] => Array ( [id] => 5 [name] => 三级类别 [level] => 2 [ParentID] => 2 )
[10] => Array ( [id] => 10 [name] => 66333666 [level] => 3 [ParentID] => 5 )
)
*/
//指定分类id,然后返回数组
function Category_array($category_id = 0,$level=0)
{
global $DB;
$sql = “SELECT * FROM category ORDER BY categoryID DESC”;
$result = $DB->query($sql);
while ($rows = $DB->fetch_array($result))
{
$category_array[$rows[‘categoryParentID’]][$rows[‘categoryID’]] = $rows;
}
foreach ($category_array AS $key=>$val)
{
if ($key == $category_id)
{
foreach ($val AS $k=> $v)
{
$options[$k] =
array(
‘id’ => $v[‘categoryID’], ‘name’ => $v[‘categoryName’], ‘level’ => $level, ‘ParentID’=>$v

[‘categoryParentID’]
);
$children = Category_array($k, $level+1);
if (count($children) > 0)
{
$options = $options + $children;
}
}
}
}
unset($category_array[$category_id]);
return $options;
}
?>
<?php
class cate
{
function Get_Category($category_id = 0,$level = 0, $default_category = 0)
{
echo $category_id;
$arr = array(
‘0’ => array(
‘1’ => array(‘id’ => 1, ‘parent’ => 0, ‘name’ => ‘1111’),
‘2’ => array(‘id’ => 2, ‘parent’ => 0, ‘name’ => ‘2222’),
‘4’ => array(‘id’ => 4, ‘parent’ => 0, ‘name’ => ‘4444’)
),
‘1’ => array(
‘3’ => array(‘id’ => 3, ‘parent’ => 1, ‘name’ => ‘333333’),
‘5’ => array(‘id’ => 5, ‘parent’ => 1, ‘name’ => ‘555555’)
),

‘3’ => array(
‘6’ => array(‘id’ => 6, ‘parent’ => 3, ‘name’ => ‘66666’),
‘7’ => array(‘id’ => 7, ‘parent’ => 3, ‘name’ => ‘77777’)
),
‘4’ => array(
‘8’ => array(‘id’ => 8, ‘parent’ => 4, ‘name’ => ‘8888’),
‘9’ => array(‘id’ => 9, ‘parent’ => 4, ‘name’ => ‘9999’)
)
);
if (!isset($arr[$category_id]))
{
return “”;
}

foreach($arr[$category_id] AS $key => $cate)
{
if ($cate[‘id’] == $default_category)
{
$txt = “<option selected value=”.$cate[‘id’].””;
}else{
$txt = “<option value=”.$cate[‘id’].””;
}

if ($level > 0)
{
$txt1 = “>” . str_repeat( “-“, $level ) . ” ” . $cate[‘name’] .

“</option>n”;
}else{
$txt1 = “>” . $cate[‘name’] . “</option>n”;
}
$val = $txt.$txt1;
echo $val;
self::Get_Category($key, $level + 1, $default_category);
}

}

function getFlush($category_id = 0,$level = 0, $default_category = 0)
{

ob_start();
self::Get_Category($category_id ,$level, $default_category);
$out = ob_get_contents();
ob_end_clean();
return $out;
}
}
$id =$_GET[‘id’];
echo “<select>”;
$c = new cate();
//$c->Get_Category();
$ttt=  $c->getFlush($id,’0′,’3′);
echo $ttt;
echo “</select>”;
?>

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