MySQL / PHP - Multi tier category structure - php

Question

I'm building a website that contains a product database. Each product belongs to a category. The structure of categories is multi-tiered and can contain any number of tiers, for example:
Electronics > Games Consoles > Xbox > Xbox One > Games > etc..
Fashion > Mens > Shirts > Long Sleeved
I always assign the product to the "last" category in the tier.
Here is the structure of my category table:
id name parent_id
================================
1 Fashion NULL
2 Mens 1
3 Shirts 2
4 Long Sleeved 3
5 Short Sleeved 3
I'm using Yii2 as my application framework, but the same concepts should apply to most MVC Frameworks, or at least those that implement an ORM like ActiveRecord.
What I want to do is:
For any category level, get the "master" parent. I.e. for Shirts it would be Fashion
For any category level, get all "last" level categories in the tier. I.e. for Mens it would be Long Sleeved and Short Sleeved.
(more advanced) For any category level, find out the number of children / parents it has.
I have the following default relations in my model:
public function getParent()
{
return $this->hasOne(Category::className(), ['id' => 'parent_id']);
}
public function getParent()
{
return $this->hasMany(Category::className(), ['parent_id' => 'id']);
}
The following is a function I have created which outputs the "tree" for any given category:
public function getParentTree()
{
$array = [];
// $this->parent refers to the 'getParent()' relation above
if(!empty($this->parent))
{
$array[] = $this->parent->name;
if(!empty($this->parent->parent))
$array[] = $this->parent->parent->name;
if(!empty($this->parent->parent->parent))
$array[] = $this->parent->parent->parent->name;
}
else
$array[] = "(none)";
$output = implode(" --> ", array_reverse($array));
return $output;
}
But there is a lot of repetition here and it looks ugly. But it is also leading me to be believe perhaps I have taken the wrong approach and need to restructure the database itself?

Answer 1

Bill I think I have resolved this issue in YII2 -> Models.
Below is my code.
public static function getSubCategories($parent_id = NULL, $level = 0)
{
// Get the Category from table
// Here you can use caching Yii::$app->cache->get to avoid multiple queries
$categories = Category::find()->select(['id', 'parent_id', 'name'])->where(['parent_id' => $parent_id])->asArray()->all();
// Logic of Nth level to return
self::$max_down_level += 1;
if($level != 0 && self::$max_down_level > $level) return $categories;
// Now for each sub categories find and return chidren as Array
foreach($categories as $key => $category)
{
$categories[$key]['children'] = self::getSubCategories($category['id'], $level);
}
return $categories;
}
Also do not forget to declare public static $max_down_level = 0; variable in your model class. and now call the function like below.
To get all the children of Parent category self::getSubCategories(NULL)
To get all the children up to 2nd level self::getSubCategories(NULL, 2)
Same way above you can declare recursive function for getting parent Categories.
public static function getParentCategories($parent_id, $level = 0)
{
// Get the Category from table
// Here you can use caching Yii::$app->cache->get to avoid multiple queries
$categories = Category::find()->select(['id', 'parent_id', 'name'])->where(['id' => $parent_id])->asArray()->all();
// Logic of Nth level to return
self::$max_up_level += 1;
if($level != 0 && self::$max_up_level > $level) return $categories;
foreach($categories as $key => $category)
{
$categories[$key]['parent'] = self::getParentCategories($category['parent_id'], $level);
}
return $categories;
}
Also do not forget to declare public static $max_up_level = 0; variable in your model class. and now call the function like below.
To get all the children of Parent category self::getParentCategories(16, 0)
To get all the children up to 2nd level self::getParentCategories(16, 2)
You can use your own class name instead of self
Hope this helps.