Mage2\Catalog\Helpers\ProductHelper::saveRelatedProducts PHP Method

    public function saveRelatedProducts($product, ProductRequest $request)
    {
        if (count($request->get('related_products')) > 0) {
            $relatedProducts = [];
            RelatedProduct::where('product_id', '=', $product->id)->delete();
            foreach ($request->get('related_products') as $relatedId) {
                $relatedProducts = ['product_id' => $product->id, 'related_product_id' => $relatedId];
                RelatedProduct::create($relatedProducts);
            }
        }
    }

 /**
  * Update the specified resource in storage.
  *
  * @param \\App\Http\Requests\ProductRequest $request
  * @param int                                $id
  *
  * @return \Illuminate\Http\Response
  */
 public function update(ProductRequest $request, $id)
 {
     try {
         $product = Product::findorfail($id);
         $this->productHelper->saveProduct($product, $request);
         $this->productHelper->saveRelatedProducts($product, $request);
         $this->productHelper->saveCategory($product, $request);
         $this->productHelper->saveProductImages($product, $request);
         $this->productHelper->saveProductAttribute($product, $request);
     } catch (\Exception $e) {
         throw new \Exception('Error in Saving Product: ' . $e->getMessage());
     }
     return redirect()->route('admin.product.index');
 }