Eloquent Query for array

Category model

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

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

In controller

$category = Category::with('children')->first();

In view

{{ $category->name }} has {{ $category->children->first()->name }}

// but better to use loop

@foreach ($category->children as $subCategory)
    {{ $subCategory->name }}
@endforeach

Thanks for the help. However, i'd love it if you could explain the inner workings of this query, finally, the query returns that the subcategory belongs to all parent category, rather than just the one for which the parent_id is specified.

That is, I have Cars, Bikes, Bicycle as parent categories, I have just a Toyota belonging to Cars Category, however it Toyota shows as subcategory for Bikes, Bicycles as well.

You need to implement many to many relationship with the self to achieve what you want.

How so sir, a subcategory can only belong to one parent category. That's the implementation as per my use case

@computermaverick I misunderstood. I'm sorry about that. I thought you wanted categories to belong to multiple.

It might be because of the 0s you stored as a default value for parent_id column. Answer by @michaloravec seems good to me. It should work.

@computermaverick Instead of default parent_id 0 set as default null, so your column parent_id should by nullable() in migration.

@michaloravec i have done as suggested however i'm only able to access the child categories. I would like that it shows the parent category as and optgroup element and then the subcategories as options under it.

That is

----->Parent Category Name
	->Subcategory 1
	->Subcategory 2 etc

@computermaverick

$categories = Category::with(['children' => function ($query) {
    $query->orderBy('name');
}])->whereNull('parent_id')->orderBy('name')->get();

<select name="category_id">
    @foreach ($categories as $category)
        <optgroup label="{{ $category->name }}">
            @foreach ($category->children as $subCategory)
                <option value="{{ $subCategory->id }}">
                    {{ $subCategory->name }}
                </option>
            @endforeach
        </optgroup>
    @endforeach
</select>

Thanks Michael, i should have thought of that. However, i still have errors. Please find below the complete codes

Category Model

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Category extends Model
{
    /**
     * The attributes that are mass assignable.
     *
     * @var array
     */
    protected $fillable = [
        'code', 'name','parent_id', 'slug', 'thumbnail',
     ];

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

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

}

Controller Logic

<?php

namespace App\Http\Controllers\Admin;
use App\Category;

use App\Http\Controllers\Controller;
use Cocur\Slugify\Slugify;
use Illuminate\Http\Request;

class CategoryController extends Controller
{
    /**
     * Display a listing of the resource.
     *
     * @return \Illuminate\Http\Response
     */
    public function index()
    {
        $categories = Category::with('children')->whereNull('parent_id')->orderBy('name', 'ASC')->get();
        return view('categories')->with('categories', $categories);
    }

Blade Template

<div class="row">
            @if(!empty($categories))
                @foreach($categories as $category)
                <div class="col-sm-12 col-lg-6 col-xl-4">
                    <div class="card card-img-holder">
                        <div class="card-body list-icons">
                            <div class="clearfix">
                                <img src="{{asset('images/categoryThumbnails/'.$category->thumbnail)}}" alt="{{ $category->name }}" title="{{ $category->name }}" width="400" height="255">
                                <h4>{{ $category->name }}</h4>
                            </div>
                            <div class="card-footer p-0">
                                @foreach($categories->children as $subcategory)
                                <p class="text-muted mb-0 pt-4">{{ $subcategory->name }}</p>
                                @endforeach
                            </div>
                        </div>
                    </div>
                </div>
                @endforeach
            @else
                <h4>No Categories Added Yet.</h4>
            @endif
        </div>

Despite all these i still get the

Property [children] does not exist on this collection instance. (View: /Applications/XAMPP/xamppfiles/htdocs/demoProject/resources/views/categories.blade.php)

Here I mentioned how your relationships have to look like.

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

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

But you have there just parent.

I know that sir. However it says children property of collection instance doesn't exist despite the fact that it does exist.

@computermaverick

@foreach($category->children as $subcategory)
    <p class="text-muted mb-0 pt-4">{{ $subcategory->name }}</p>
@endforeach

$category not $categories

Thanks buddy.