我已经建立了一个"无限深度"分类系统，该系统存储在数据库中，其中包含三条重要信息：
- 类别ID
- 父类别ID
- NodePath
前两个是不言自明的，但最后一个需要澄清。如果类别是#20，其父级是#10，父级是#5，则NodePath看起来像5:10:20。通过这种方式，我可以递归地找到一个类别父分支。
我正在寻找一种方法，从数据库中获取每个类别，然后以某种方式对它们进行排序，结果是这样的数组：
array(
0 => array(
3 => array(
7,
13,
),
5,
),
1 => array(
6,
9
),
);
本质上，这是根据前面描述的NodePath结构创建的树层次结构的映射。
我想出了这样的东西：
$tree = array();
foreach( $categories as $category )
{
// A NodePath Example is "1:7:13:24" where 1 is the root category,
// 24 is the "leaf" or end node, and the other numbers are sub categories
// in order.
$nodes = explode( ":", $category->NodePath );
$lastNode = &$tree;
foreach( $nodes as $node )
{
// Add New Branch if not Termination
if( !isset( $lastNode[ $node ] ) && $node != end($nodes) )
$lastNode[ $node ] = array();
// Recursive Addressing
$lastNode = &$lastNode[ $node ];
}
}
它生成树的var_dump()（与我的数据库中的数据匹配）：
array (size=3)
1 =>
array (size=1)
4 => null
2 =>
array (size=2)
5 =>
array (size=1)
7 => &null
6 => null
3 => null
第三个深度向下将终端节点设置为"&null"，而不仅仅是"null"。我该怎么解决这个问题？
它只发生在数组中的最后一个项上，因此修复它的一种方法是在$categories的末尾添加一个NULL值，然后用array_filter:将其删除
$categories = [
(object)['NodePath' => '1'],
(object)['NodePath' => '1:4'],
(object)['NodePath' => '2'],
(object)['NodePath' => '2:5:7'],
(object)['NodePath' => '2:6'],
(object)['NodePath' => '3'],
(object)['NodePath' => '2:5'],
(object)['NodePath' => '3:1']
];
$tree = array();
$categories[] = (object)array('NodePath' => NULL);
foreach( $categories as $category ){
$nodes = explode( ":", $category->NodePath );
$lastNode = &$tree;
foreach( $nodes as $node ){
// Add New Branch if not Termination
if( !isset( $lastNode[ $node ] ) && $node != end($nodes) ){
$lastNode[ $node ] = array();
}
// Recursive Addressing
$lastNode = &$lastNode[ $node ];
}
}
$tree = array_filter($tree);
var_dump($tree);
这是一个转储，它在最后一个值之前有&。我还尝试重新排列categories数组中的元素，结果也一样。
array(3) { [1]=> array(1) { [4]=> NULL } [2]=> array(2) { [5]=> array(1) { [7]=> NULL } [6]=> NULL } [3]=> array(1) { [1]=> NULL } }
<?php
function builTree($categories){
$tree = array();
foreach($categories as $category){
$path = explode( ":", $category->NodePath );
$lastNode = &$tree;
for($deep=0;$deep<count($path);$deep++){
if(!is_array($lastNode[$path[$deep]])) {
if($deep==count($path)-1) { $lastNode[$path[$deep]] = null;}
else {$lastNode[$path[$deep]] = array(); $lastNode = &$lastNode[$path[$deep]];}
} else {$lastNode = &$lastNode[$path[$deep]];}
}
}
return $tree;
}
echo "<pre>";
// works with full tree given
$categories = [
(object)['NodePath' => '1'],
(object)['NodePath' => '1:4'],
(object)['NodePath' => '2'],
(object)['NodePath' => '2:5:7:90:23'],
(object)['NodePath' => '2:6'],
(object)['NodePath' => '3'],
(object)['NodePath' => '2:5'],
(object)['NodePath' => '3:1'] // even works with loop paths
];
print_r(builTree($categories));
// works even if just leafs are given
$categories = [
(object)['NodePath' => '2:5:7:90:23'],
(object)['NodePath' => '2:5:7:66:21']
];
print_r(builTree($categories));