How to create a nested-list of categories in Laravel?

问题

How can I create a nested list of categories in Laravel?

I want to create something like this:

• --- Php
• ------ Laravel
• --------- Version
• ------------ V 5.7
• --- Python
• ------ Django
• --- Ruby
• ..........

My table's fields are:

id | name | parent_id

If I have to add another column like depth, please tell me.

I am using this following code, but I think it is not the best solution for creating nested-list of categories besides, I can not pass this function to my view.

function rec($id)
{
     $model = Category::find($id);
     foreach ($model->children as $chield) rec($chield->id);
     return $model->all();
}

function main () {
    $models = Category::whereNull('parent_id')->get();
    foreach ($models as $parent) return rec($parent->id);
}

回答1:

You can make a self-referential model:

class Category extends Model {

    public function parent()
    {
        return $this->belongsTo('Category', 'parent_id');
    }

    public function children()
    {
        return $this->hasMany('Category', 'parent_id');
    }
}

and make a recursive relation:

// recursive, loads all descendants
public function childrenRecursive()
{
   return $this->children()->with('childrenRecursive');
}

and to get parents with all their children:

$categories = Category::with('childrenRecursive')->whereNull('parent')->get();

Lastly you need to just iterate through the children until children is null. There can definitely be some performance issues with this if you are not careful. If this is a fairly small dataset that you plan to remain that way it shouldn't be an issue. If this is going to be an ever growing list it might make sense to have a root_parent_id or something to query off of and assemble the tree manually.

回答2:

Searching for something somehow in this area I wanted to share a functionality for getting the depth level of child:

    function getDepth($category, $level = 0) {
    if ($category->parent_id>0) {
        if ($category->parent) {
                $level++;
                return $this->getDepth($category->parent, $level);
            }
        }
       return $level;
    }

Maybe it will help someone! Cheers!

回答3:

If someone needs a better answer look up my answer, it helped me, when I had faced with such a problem.

   class Category extends Model {

     private $descendants = [];

     public function children()
        {
            return $this->subcategories()->with('children');
        }

     public function hasChildren(){
            if($this->children->count()){
                return true;
            }

            return false;
        }

     public function findDescendants(Category $category){
            $this->descendants[] = $category->id;

            if($category->hasChildren()){
                foreach($category->children as $child){
                    $this->findDescendants($child);
                }
            }
        }

      public function getDescendants(Category $category){
            $this->findDescendants($category);
            return $this->descendants;
        }
 }

And In your Controller just test this:

$category = Category::find(1);
$category_ids = $category->getDescendants($category);

It will result ids in array all descendants of your category where id=1. then :

$products = Product::whereIn('category_id',$category_ids)->get();

You are welcome =)

回答4:

The problem is solved!

View:

    $traverse = function ($categories) use (&$traverse) {
        foreach ($categories as $category) $traverse($cat->Children);
    };
    $traverse(array ($category));

Model:

public function Children()
{
    return $this->hasMany($this, 'parent');
}

public function Parent()
{
    return $this->hasOne($this,'id','parent');
}

来源：https://stackoverflow.com/questions/43989728/how-to-create-a-nested-list-of-categories-in-laravel