How to get many to many relationship items in laravel

Assuming Laravel Model classes - Series, Category and Product

For the Series Model Class, create a function

   public function categories()   {        return $this->belongsToMany('App\Category');   }

For the Category Model Class, create a function

   public function products()   {        return $this->belongsToMany('App\products');   }

Now for a given Series, you can easily retrieve all related categories using thesimple function call

$categories = $series->categories();

Finally coming to the main problem of showing products under multiple categories.

for($categories as $category){     $productsOfThisCategory = $categories->products();     //save into some other data structure, say an array $allProducts}

$allProducts will have multi-category products for a specific Series.

Refer : Standard eloquent relationship -Many to Many

You can use this answer for sorting.

How to sort by a field of the pivot table of a many-to-many relationship in Eloquent ORM

If I understand you correctly, then your models looks like below

class Series extends Model{    // other code    public function categories() {        return $this->belongsToMany('App\Category');    }    // other code}class Category extends Model{    // other code    public function series() {        return $this->belongsToMany('App\Series');    }    public function products() {        return $this->belongsToMany('App\Product');    }    // other code}class Product extends Model{    // other code    public function categories() {        return $this->belongsToMany('App\Category');    }    // other code}

Further to get all products of certain series you need to do so

public function view($series = 0, $cat = 0, $page = 1){    if (!empty($series)) {        $seria = Series::with(['categories' => function($query) {            $query->with('products');        })->find($series);        // or may be this will work, don't know        // Series::with('categories.products')->find($series);        // get all caegories from seria or certain one        if (empty($cat)) {            $categories = $seria->categories;         }        else {            $categories = $seria->categories()->where('id', $cat)->get;         }        // retrieve produts form each category and making from them collection        $products = $categories->map(function($category) {            return $category->products;        })->flatten();        // or use this approach if above not working        /*$products = collect([]);        foreach ($categories as $category) {            $produts = $products->merge($category->products);        }*/        // do your magic    }    else {        // not exactly understand what you want to do when $series is not set    }    // do your magic}