hasOne( Unit::class, 'id', 'unit_id' ); } public function product() { return $this->hasOne( Product::class, 'id', 'product_id' ); } public function parent() { return $this->hasOne( Product::class, 'id', 'parent_id' ); } public function unit_quantity() { return $this->hasOne( ProductUnitQuantity::class, 'id', 'unit_quantity_id' ); } }