Laravel模型中的变量值丢失了

Question

I have this code in my Product model:

    /**
     * Get product's attributes.
     *
     * @return array
     */
    public function attributes()
    {
        $nestedAttributes = [];

        foreach ($this->attributeGroups as $attributeGroup)
        {
            print_r($attributeGroup);

            if (isset($this->{$attributeGroup->code}))
            {
                dd($attributeGroup);

                $attributes = json_decode($this->{$attributeGroup->code});

                foreach ($attributes as $key => $attribute)
                {
                    $nestedAttributes[ $key ] = $attribute;
                }
            }
        }

        return $nestedAttributes;
    }

Then in my controller:

$product = Product::with('children')->find(9);
$product->attributes();

The problem was print_r($attributeGroup); printed out the App\AttributeGroup Object but dd($attributeGroup); printed out a empty array. I don't know why it printed 2 difference values while it was just a variable name.