Add methods to add and remove Items from a Cart.

app/Models/Cart.php

@@ -8,6 +8,7 @@ use Illuminate\Database\Eloquent\Relations\BelongsToMany;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
 
 use App\Models\City;
+use Brick\Math\BigInteger;
 
 class Cart extends Model
 {
@@ -51,6 +52,22 @@ class Cart extends Model
         $this->save();
     }
 
+    public function addItem(BigInteger $item) {
+        $this->items()->sync($item);
+    }
+
+    public function addItems(array $items) {
+        $this->items()->sync($items);
+    }
+
+    public function removeItem(BigInteger $item) {
+        $this->items()->sync($item);
+    }
+
+    public function removeItems(array $items) {
+        $this->items()->sync($items);
+    }
+
     public function dropItems() {
         $this->items()->detach();
     }