PHP实现无限极归类

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"><span class="hljs-variable">$categories</span> = <span class="hljs-keyword">array</span>(    <span class="hljs-keyword">array</span>(<span class="hljs-string">'id'</span>=><span class="hljs-number">1</span>,<span class="hljs-string">'name'</span>=><span class="hljs-string">'电脑'</span>,<span class="hljs-string">'pid'</span>=><span class="hljs-number">0</span>),    <span class="hljs-keyword">array</span>(<span class="hljs-string">'id'</span>=><span class="hljs-number">2</span>,<span class="hljs-string">'name'</span>=><span class="hljs-string">'手机'</span>,<span class="hljs-string">'pid'</span>=><span class="hljs-number">0</span>),    <span class="hljs-keyword">array</span>(<span class="hljs-string">'id'</span>=><span class="hljs-number">3</span>,<span class="hljs-string">'name'</span>=><span class="hljs-string">'笔记本'</span>,<span class="hljs-string">'pid'</span>=><span class="hljs-number">1</span>),    <span class="hljs-keyword">array</span>(<span class="hljs-string">'id'</span>=><span class="hljs-number">4</span>,<span class="hljs-string">'name'</span>=><span class="hljs-string">'台式机'</span>,<span class="hljs-string">'pid'</span>=><span class="hljs-number">1</span>),    <span class="hljs-keyword">array</span>(<span class="hljs-string">'id'</span>=><span class="hljs-number">5</span>,<span class="hljs-string">'name'</span>=><span class="hljs-string">'智能机'</span>,<span class="hljs-string">'pid'</span>=><span class="hljs-number">2</span>),    <span class="hljs-keyword">array</span>(<span class="hljs-string">'id'</span>=><span class="hljs-number">6</span>,<span class="hljs-string">'name'</span>=><span class="hljs-string">'功能机'</span>,<span class="hljs-string">'pid'</span>=><span class="hljs-number">2</span>),    <span class="hljs-keyword">array</span>(<span class="hljs-string">'id'</span>=><span class="hljs-number">7</span>,<span class="hljs-string">'name'</span>=><span class="hljs-string">'超级本'</span>,<span class="hljs-string">'pid'</span>=><span class="hljs-number">3</span>),    <span class="hljs-keyword">array</span>(<span class="hljs-string">'id'</span>=><span class="hljs-number">8</span>,<span class="hljs-string">'name'</span>=><span class="hljs-string">'游戏本'</span>,<span class="hljs-string">'pid'</span>=><span class="hljs-number">3</span>),);</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"><span class="hljs-keyword">array</span>(    <span class="hljs-comment">//1对应$categories中的id ，方便直接读取</span>    <span class="hljs-number">1</span> => <span class="hljs-keyword">array</span>(        <span class="hljs-string">'id'</span>=><span class="hljs-number">1</span>,        <span class="hljs-string">'name'</span>=><span class="hljs-string">'电脑'</span>,        <span class="hljs-string">'pid'</span>=><span class="hljs-number">0</span>,        children=><span class="hljs-keyword">array</span>(            &<span class="hljs-keyword">array</span>(                <span class="hljs-string">'id'</span>=><span class="hljs-number">3</span>,                <span class="hljs-string">'name'</span>=><span class="hljs-string">'笔记本'</span>,                <span class="hljs-string">'pid'</span>=><span class="hljs-number">1</span>,                <span class="hljs-string">'children'</span>=><span class="hljs-keyword">array</span>(                    <span class="hljs-comment">//此处省略</span>                )            ),            &<span class="hljs-keyword">array</span>(                <span class="hljs-string">'id'</span>=><span class="hljs-number">4</span>,                <span class="hljs-string">'name'</span>=><span class="hljs-string">'台式机'</span>,                <span class="hljs-string">'pid'</span>=><span class="hljs-number">1</span>,                <span class="hljs-string">'children'</span>=><span class="hljs-keyword">array</span>(                    <span class="hljs-comment">//此处省略</span>                )            ),        )    ),    <span class="hljs-comment">//其他分类省略</span>)</code>

2. 处理过程：

<code class=" hljs php"><span class="hljs-variable">$tree</span> = <span class="hljs-keyword">array</span>();<span class="hljs-comment">//第一步，将所有的分类id作为数组key,并创建children单元</span><span class="hljs-keyword">foreach</span>(<span class="hljs-variable">$categories</span> <span class="hljs-keyword">as</span> <span class="hljs-variable">$category</span>){    <span class="hljs-variable">$tree</span>[<span class="hljs-variable">$category</span>[<span class="hljs-string">'id'</span>]] = <span class="hljs-variable">$category</span>;    <span class="hljs-variable">$tree</span>[<span class="hljs-variable">$category</span>[<span class="hljs-string">'id'</span>]][<span class="hljs-string">'children'</span>] = <span class="hljs-keyword">array</span>();}<span class="hljs-comment">//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。</span><span class="hljs-keyword">foreach</span> (<span class="hljs-variable">$tree</span> <span class="hljs-keyword">as</span> <span class="hljs-variable">$key</span>=><span class="hljs-variable">$value</span>) {    <span class="hljs-keyword">if</span> (<span class="hljs-variable">$value</span>[<span class="hljs-string">'pid'</span>] != <span class="hljs-number">0</span>) {        <span class="hljs-variable">$tree</span>[<span class="hljs-variable">$value</span>[<span class="hljs-string">'pid'</span>]][<span class="hljs-string">'children'</span>][] = &<span class="hljs-variable">$tree</span>[<span class="hljs-variable">$key</span>];    }}print_r(<span class="hljs-variable">$tree</span>);</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"><span class="hljs-keyword">Array</span>(    [<span class="hljs-number">1</span>] => <span class="hljs-keyword">Array</span>        (            [id] => <span class="hljs-number">1</span>            [name] => 电脑            [pid] => <span class="hljs-number">0</span>            [children] => <span class="hljs-keyword">Array</span>                (                    [<span class="hljs-number">0</span>] => <span class="hljs-keyword">Array</span>                        (                            [id] => <span class="hljs-number">3</span>                            [name] => 笔记本                            [pid] => <span class="hljs-number">1</span>                            [children] => <span class="hljs-keyword">Array</span>                                (                                    [<span class="hljs-number">0</span>] => <span class="hljs-keyword">Array</span>                                        (                                            [id] => <span class="hljs-number">7</span>                                            [name] => 超级本                                            [pid] => <span class="hljs-number">3</span>                                            [children] => <span class="hljs-keyword">Array</span>                                                (                                                )                                        )                                    [<span class="hljs-number">1</span>] => <span class="hljs-keyword">Array</span>                                        (                                            [id] => <span class="hljs-number">8</span>                                            [name] => 游戏本                                            [pid] => <span class="hljs-number">3</span>                                            [children] => <span class="hljs-keyword">Array</span>                                                (                                                )                                        )                                )                        )                    [<span class="hljs-number">1</span>] => <span class="hljs-keyword">Array</span>                        (                            [id] => <span class="hljs-number">4</span>                            [name] => 台式机                            [pid] => <span class="hljs-number">1</span>                            [children] => <span class="hljs-keyword">Array</span>                                (                                )                        )                )        )    [<span class="hljs-number">2</span>] => <span class="hljs-keyword">Array</span>        (            [id] => <span class="hljs-number">2</span>            [name] => 手机            [pid] => <span class="hljs-number">0</span>            [children] => <span class="hljs-keyword">Array</span>                (                    [<span class="hljs-number">0</span>] => <span class="hljs-keyword">Array</span>                        (                            [id] => <span class="hljs-number">5</span>                            [name] => 智能机                            [pid] => <span class="hljs-number">2</span>                            [children] => <span class="hljs-keyword">Array</span>                                (                                )                        )                    [<span class="hljs-number">1</span>] => <span class="hljs-keyword">Array</span>                        (                            [id] => <span class="hljs-number">6</span>                            [name] => 功能机                            [pid] => <span class="hljs-number">2</span>                            [children] => <span class="hljs-keyword">Array</span>                                (                                )                        )                )        )    [<span class="hljs-number">3</span>] => <span class="hljs-keyword">Array</span>        (            [id] => <span class="hljs-number">3</span>            [name] => 笔记本            [pid] => <span class="hljs-number">1</span>            [children] => <span class="hljs-keyword">Array</span>                (                    [<span class="hljs-number">0</span>] => <span class="hljs-keyword">Array</span>                        (                            [id] => <span class="hljs-number">7</span>                            [name] => 超级本                            [pid] => <span class="hljs-number">3</span>                            [children] => <span class="hljs-keyword">Array</span>                                (                                )                        )                    [<span class="hljs-number">1</span>] => <span class="hljs-keyword">Array</span>                        (                            [id] => <span class="hljs-number">8</span>                            [name] => 游戏本                            [pid] => <span class="hljs-number">3</span>                            [children] => <span class="hljs-keyword">Array</span>                                (                                )                        )                )        )    [<span class="hljs-number">4</span>] => <span class="hljs-keyword">Array</span>        (            [id] => <span class="hljs-number">4</span>            [name] => 台式机            [pid] => <span class="hljs-number">1</span>            [children] => <span class="hljs-keyword">Array</span>                (                )        )    [<span class="hljs-number">5</span>] => <span class="hljs-keyword">Array</span>        (            [id] => <span class="hljs-number">5</span>            [name] => 智能机            [pid] => <span class="hljs-number">2</span>            [children] => <span class="hljs-keyword">Array</span>                (                )        )    [<span class="hljs-number">6</span>] => <span class="hljs-keyword">Array</span>        (            [id] => <span class="hljs-number">6</span>            [name] => 功能机            [pid] => <span class="hljs-number">2</span>            [children] => <span class="hljs-keyword">Array</span>                (                )        )    [<span class="hljs-number">7</span>] => <span class="hljs-keyword">Array</span>        (            [id] => <span class="hljs-number">7</span>            [name] => 超级本            [pid] => <span class="hljs-number">3</span>            [children] => <span class="hljs-keyword">Array</span>                (                )        )    [<span class="hljs-number">8</span>] => <span class="hljs-keyword">Array</span>        (            [id] => <span class="hljs-number">8</span>            [name] => 游戏本            [pid] => <span class="hljs-number">3</span>            [children] => <span class="hljs-keyword">Array</span>                (                )        ))</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。

原文 http://blog.csdn.net/u013927110/article/details/44086253