The rewritten title is: What causes a "possible infinite loop" when accessing another model attribute in an appended attribute of a model?

Question

My Laravel 9 application has two models: the brand model and the product model. Each product belongs to one brand, and one brand belongs to multiple products (1: n relationship). The product model should provide a "calculated" (additional) property called title_medium that concatenates the brand title and product title upon request.

Once I try to access $this->brand in the product model's getTitleMediumAttribute() method, xdebug The possibleInfiniteloop exception will be thrown and execution will be canceled (after N iterations). I think this has something to do with relationships and load sequences (eager loading) but I can't find a solution so far.

Brand Model

The

brand model has an attribute title and has a number of products belonging to brand.

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\HasMany;
use Illuminate\Support\Str;

class Brand extends Model
{
    use HasFactory;

    /*** Additional attributes for this model*/
    protected $appends = [
        'prices'
    ];

    protected $fillable = [
        'title'
    ];

    /*** The "booted" method of the model.
     *
     * @return void*/
    protected static function booted()
    {
        static::creating(function ($brand) {
            $brand->slug = Str::slug($brand->title, '-', 'de');
        });
    }

    /*** Returns all products for a brand
     *
     * @return HasMany*/
    public function products(): HasMany
    {
        return $this->hasMany(Product::class);
    }
}

Product model number

Each product belongs to a brand. The additional attribute title_medium should concatenate the brand title and product title.

namespace App\Models;

class Product extends Model
{
    use HasFactory, Searchable, Filterable;

    protected $fillable = [
        'title',
        'brand_id',
        'image'
    ];

    /*** Additional attributes for this model*/
    protected $appends = [
        'title_long',
        'lowest_price',
        'highest_discount_percent_price',
        'latest_price_date',
        'price_count'
    ];

    /*** The "booted" method of the model.
     *
     * @return void*/
    protected static function booted()
    {
        static::creating(function ($product) {
            $product->slug = Str::slug($product->title_long, '-', 'de');
        });
    }

    /*** Product belongs to one brand*/
    public function brand(): BelongsTo
    {
        return $this->belongsTo(Brand::class);
    }

    /*** Get the combined title from product and brand*/
    public function getTitleMediumAttribute(): string
    {
        // THIS CAUSES A "POSSIBLE INFINITE LOOP EXCEPTION" in xdebug
        return $this->brand->title . ' ' . $this->title;
    }
}

Answer 1

Try using attribute instead of getTitleMediumAttribute, like this and tell me if you still get the same error (using this method instead of `getTitleMediumAttribute):

public function titleMedium(): Attribute
{
    return Attribute::get(
        fn () => "{$this->brand->title} $this->title",
    );
}

Attribute is \Illuminate\Database\Eloquent\Casts\Attribute