recursive function category database

问题:

i hoping to create a recursive function which i don't have an idea yet

this is my code to fetch category from database

  <?php   $sql = mysql_query("SELECT * FROM categories WHERE category_parent = '1' ORDER BY lft ASC");   while($row = mysql_fetch_array($sql)) {   echo "<li><a href='/{$row['category_safe_name']}/'>{$row['category_name']}</a>";   $sql2 = mysql_query("SELECT * FROM categories WHERE category_parent = '{$row['category_id']}'");   if(mysql_num_rows($sql2) > 0)   echo "<ul>";   while($row2 = mysql_fetch_array($sql2)) {   echo "<li><a href='/{$row2['category_safe_name']}/'>{$row2['category_name']}</a><li>";   }   if(mysql_num_rows($sql2) > 0)   echo "</ul>";   echo "</li>";   }   ?> 

Currently This look like

Top Category (category_id = 1)    Category        Sub Category 

My code works for category & subcategory. What i'm planning to do is to make my code to support unlimited subcategories

Any help and advise are welcomed.

Thank you

回答1:

I would do :

<?php function getChildren($id=1) {   $sql = mysql_query("SELECT * FROM categories WHERE category_parent = '$id' ORDER BY lft ASC");   echo "<ul>";   while($row = mysql_fetch_array($sql)) {     echo "<li><a href='/{$row['category_safe_name']}/'>{$row['category_name']}</a>";     getChildren($row['category_id']);     echo "</li>";   }   echo "</ul>"; }  getChildren(); ?> 

回答2:

You should have a look at Managing Hierarchical Data in MySQL.

It gives a good overview of some approaches to using hierarchical data in MySQL.

回答3:

What you need to do, is build a recursive function. That is, a function that calls itself within. An example:

function getCategories($parent=0) {     $res = mysql_query("SELECT * FROM categories WHERE category_parent = '$id' ORDER BY left ASC");     if (mysql_num_rows($res) > 0) {         $category = mysql_fetch_object();         echo '<ul>';         echo '<li><a href="' . $category->category_safe_name . '">' . $category->category_name . '</a>';         getCategories($category->category_id);         echo '</li>';     } } 

If I've made any typos in regards to table and column names then obviously swap them out for the correct values.

回答4:

Something like this?

function getCategories($mid, $categoryParent = 1) {     $return = '';     $results = mysql_query("SELECT * FROM categories WHERE category_parent = '$categoryParent' ORDER BY lft ASC", $mid);     while($row = mysql_fetch_array($results)) {         $return .= "<li><a href='/{$row['category_safe_name']}/'>{$row['category_name']}</a></li>";         $subs = getCategories($mid, $row['category_id']);         if (!empty($subs)) {             $return .= '<ul>';             $return .= $subs;             $return .= '<ul>';         }     }     return $return; }  $mid = mysql_connect($host, $user, $pass); echo getCategories($mid); 

Would print out all your categories, of course fix it to exactly how you want, but that should give you an idea of how recursive functions could work

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