PHP实现无限极分类
利用两个for循环实现无限级分类
表:
| 字段名 | 字段类型 | 备注 | 默认值 |
|---|---|---|---|
| id | int | 主键 auto-increment | |
| name | varchar | 分类名称 | |
| pid | int | 父类id | 0 |
顶级分类的 pid 默认就是0了。当我们想取出某个分类的子分类树的时候，基本思路就是递归，当然，出于效率问题不建议每次递归都查询数据库，通常的做法是先将所有分类取出来，数据保存到PHP数组里，再进行处理，最后还可以将结果缓存起来以提高下次请求的效率。
先来构建一个原始数组，这个直接从数据库中查询出来就行：
1. 构建数据
<code class="hljs php">$categories = array(
array('id'=>1,'name'=>'电脑','pid'=>0),
array('id'=>2,'name'=>'手机','pid'=>0),
array('id'=>3,'name'=>'笔记本','pid'=>1),
array('id'=>4,'name'=>'台式机','pid'=>1),
array('id'=>5,'name'=>'智能机','pid'=>2),
array('id'=>6,'name'=>'功能机','pid'=>2),
array('id'=>7,'name'=>'超级本','pid'=>3),
array('id'=>8,'name'=>'游戏本','pid'=>3),
);</code>
目标是将它转化为下面这种结构
电脑 >笔记本 >>超级本 >> 游戏本 > 台式机
手机 > 智能机 > 功能机
用数组来表示的话，可以增加一个 children 键来存储它的子分类：
<code class="hljs php">array(
//1对应$categories中的id ，方便直接读取
1 => array(
'id'=>1,
'name'=>'电脑',
'pid'=>0,
children=>array(
&array(
'id'=>3,
'name'=>'笔记本',
'pid'=>1,
'children'=>array(
//此处省略
)
),
&array(
'id'=>4,
'name'=>'台式机',
'pid'=>1,
'children'=>array(
//此处省略
)
),
)
),
//其他分类省略
)</code>
2. 处理过程：
<code class="hljs php">$tree = array();
//第一步，将所有的分类id作为数组key,并创建children单元
foreach($categories as $category){
$tree[$category['id']] = $category;
$tree[$category['id']]['children'] = array();
}
//第二步，利用引用，将每个分类添加到父类children数组中，这样一次遍历即可形成树形结构。
foreach ($tree as $key=>$value) {
if ($value['pid'] != 0) {
$tree[$value['pid']]['children'][] = &$tree[$key];
}
}
print_r($tree);</code>
<code>注:必须通过引用, 否则不会一次遍历就生成最终的结果. </code>
3. 打印结果如下：
<code class="hljs php">Array
(
[1] => Array
(
[id] => 1
[name] => 电脑
[pid] => 0
[children] => Array
(
[0] => Array
(
[id] => 3
[name] => 笔记本
[pid] => 1
[children] => Array
(
[0] => Array
(
[id] => 7
[name] => 超级本
[pid] => 3
[children] => Array
(
)
)
[1] => Array
(
[id] => 8
[name] => 游戏本
[pid] => 3
[children] => Array
(
)
)
)
)
[1] => Array
(
[id] => 4
[name] => 台式机
[pid] => 1
[children] => Array
(
)
)
)
)
[2] => Array
(
[id] => 2
[name] => 手机
[pid] => 0
[children] => Array
(
[0] => Array
(
[id] => 5
[name] => 智能机
[pid] => 2
[children] => Array
(
)
)
[1] => Array
(
[id] => 6
[name] => 功能机
[pid] => 2
[children] => Array
(
)
)
)
)
[3] => Array
(
[id] => 3
[name] => 笔记本
[pid] => 1
[children] => Array
(
[0] => Array
(
[id] => 7
[name] => 超级本
[pid] => 3
[children] => Array
(
)
)
[1] => Array
(
[id] => 8
[name] => 游戏本
[pid] => 3
[children] => Array
(
)
)
)
)
[4] => Array
(
[id] => 4
[name] => 台式机
[pid] => 1
[children] => Array
(
)
)
[5] => Array
(
[id] => 5
[name] => 智能机
[pid] => 2
[children] => Array
(
)
)
[6] => Array
(
[id] => 6
[name] => 功能机
[pid] => 2
[children] => Array
(
)
)
[7] => Array
(
[id] => 7
[name] => 超级本
[pid] => 3
[children] => Array
(
)
)
[8] => Array
(
[id] => 8
[name] => 游戏本
[pid] => 3
[children] => Array
(
)
)
)</code>
优点：关系清楚，修改上下级关系简单。
缺点：使用PHP处理，如果分类数量庞大，效率也会降低。
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