I want to retrieve database values in category name and i want to show default value in selection. This is my controller for my edit view.

I have a category_product table.

<div class="col-md-4">
    <div class="form-group">
        <label for="category">category</label>
        <select class="form-control" name="category" id="category">
            @foreach($categories as $category)
                <option value="{{ $category->id }}" {{ $product->categories()->category_id == $category->id ? 'selected' : '' }}>{{ $category->name }}</option>
            @endforeach
        </select>
    </div>
</div>

ProductController.php

public function edit(Product $product)
{
    $categories = Category::all();
    return view('Admin.products.edit', compact('product', 'categories'));
}

Product.php

public function categories()
{
    return $this->belongsToMany(Category::class);
}

I get this error.

Undefined property: Illuminate\Database\Eloquent\Relations\BelongsToMany::$category_id