Seeking Guidance: Eloquent Relationship Behavior with binary(16) UUID Primary/Foreign Keys

First, I apologize if this is something easy. I have been using Laravel for a few months and do not have the breadth of experience to figure out all the caveats or possibilities. This post concerns a Laravel 12 (PHP 8.3.6) REST API backend, typically deployed with MariaDB. A core architectural decision involves using UUIDs for primary and foreign keys. This implementation historically utilized BINARY(16) columns in the database, managed by a custom BinaryUuidCast and a HasUuidKeyCreation trait to convert string UUIDs (e.g., UUIDv7) to binary and vice-versa. The Tyman/JWT package handles authentication. At the end of the day, if this is a mistake I am making and there is no underlying issue with the framework, that is the best-case scenario and I will eat the crow.

Problem Description

I'm encountering unexpected behavior where Eloquent relationships (specifically a hasMany relationship in this case) do not resolve as anticipated when models use binary(16) columns for primary and foreign keys. When attempting to access a related model through the relationship, it consistently returns null, even though valid binary(16) foreign key data is present in the database. I've observed that switching the primary and foreign keys to string-based UUIDs (uuid() in migrations) allows the relationships to function correctly. My gut tells me this could be related to how Eloquent handles collection hydrating or how accessors might interact with binary keys in certain contexts. I haven't thoroughly explored the Laravel framework code to pinpoint the exact mechanism.

Steps to Reproduce

1. Define Models and Relationship: Create two Eloquent models, for example, User and Profile, where User has a hasMany relationship to Profile.

   public function profiles()
   {
       return $this->hasMany(Profile::class);
   }
   

   public function user()
   {
       return $this->belongsTo(User::class);
   }
   

2. Configure Migrations with binary(16): Ensure both users and profiles table migrations define their primary keys (id) and the foreign key (user_id on profiles) as binary(16) columns.

       Schema::create('users', function (Blueprint $table) {
   
           // Primary Key
   
           $table->uuid('id', 16)->primary();
   // ... other columns
   

   Schema::create('profiles', function (Blueprint $table) {
   
           // Primary Key
   
           $table->uuid('id', 16)->primary();
   
           // Foreign Key (User)
   
           $table->uuid('user_id', 16);
           $table->foreign('user_id')
               ->references('id')
               ->on('users')
               ->onDelete('cascade');
   

3. Implement Binary UUID Generation: Utilize a custom trait or similar logic (e.g., HasUuidKeyCreation as provided in the "Relevant Code Snippets" section) in the models to generate and store binary(16) UUIDs for the primary keys.
4. Populate Data: Ensure records exist in both tables with valid binary(16) primary and foreign key values establishing the relationship.
5. Access Relationship via Accessor: In the Profile model, create an accessor that attempts to access an attribute from the related User model.

   public function getAgeAttribute()
   {
       return $this->age_override ?? $this->user?->age;
   }
   

6. Trigger Relationship Access: Execute a query to retrieve a Profile model and implicitly trigger the accessor.

   // Via Tinker or application code
   Profile::inRandomOrder()->first();
   

Expected Behavior

When accessing $this->user?->age within the Profile model's getAgeAttribute(), the $this->user relationship is expected to correctly resolve to the associated User model instance, allowing access to its age attribute (which is itself derived from a getAgeAttribute accessor on the User model, confirming underlying data validity).

Actual Behavior

The $this->user relationship consistently returns null, even when the profiles.user_id foreign key correctly contains the binary(16) primary key of an existing User record. This prevents access to any related User model attributes.

Relevant Code Snippets

1. Profile Model Accessor:

public function getAgeAttribute()
{
    return $this->age_override ?? $this->user?->age;
}

2. User Model Accessor:

public function getAgeAttribute()
{
    $birthday = $this->birthday;

    return $birthday ? intval(Carbon::parse($birthday)->age) : null;
}

3. Custom Trait for Binary UUID Key Generation:

protected static function bootHasUuidKeyCreation()
{
static::creating(function ($model) {

// Create the unique v7 uuid PK for the model record.

        if (empty($model->getKey())) {

            $maxAttempts = 5;
            $attempts = 0;

            do {
                $uuid     = Uuid::uuid7()->toString();
                $binaryId = $uuid; // hex2bin(str_replace('-', '', $uuid));
                $attempts++;

                if ($attempts > $maxAttempts) {

                    // If this ever fires ... buy a lottery ticket.

                    throw new \Exception("Failed to generate a unique UUID after {$maxAttempts} attempts.");
                }
            } while (static::where($model->getKeyName(), $binaryId)->exists());

            $model->{$model->getKeyName()} = $binaryId;
        }
    });
}

Crucial Observation / Workaround

It has been observed that the relationship resolution issue disappears and relationships function correctly when the database schema and model configuration are changed from binary(16) UUIDs to string-based UUIDs:

• All primary and foreign key columns in migrations are changed from binary(16) to uuid().
• Corresponding model casts for UUIDs (if any were used for binary handling) are removed.
• The custom HasUuidKeyCreation trait (or similar logic for binary UUID generation) is removed, relying on standard Laravel string UUID handling.

Environment

• Laravel Version: 12.15
• PHP Version: 8.3.6
• Database Driver & Version: MariaDB 11.7
• UUID Library: ramsey/uuid
• Deployment Environment: GitHub moztopia/devlite container customized for Laravel