Creating related Models on Laravel/Eloquent relations with primary key type UUID - sql

Question

Laravel: 7; PHP: 7.4/8.0
In my project I have two related models: User and TimeAccount. Both use UUID for their primary key, the key name is still id.
Migrations:
class CreateUsersTable extends Migration
{
public function up()
{
Schema::create('users', function (Blueprint $table) {
$table->uuid('id')->primary();
// snip...
});
}
// snip...
}
class CreateTimeAccountsTable extends Migration
{
public function up()
{
Schema::create('time_accounts', function (Blueprint $table) {
$table->uuid('id')->primary();
$table->foreignUuid('user_id')->nullable()->constrained();
// snip...
});
}
// snip...
}
Models:
class User
{
use IsIdentifiedByUuid;
protected $keyType = 'string';
public function timeAccount()
{
return $this->hasOne(TimeAccount::class);
}
// snip...
}
class TimeAccount
{
use IsIdentifiedByUuid;
protected $keyType = 'string';
public function user()
{
return $this->belongsTo(User::class);
}
// snip...
}
IsIdentifiedByUuid Trait:
trait IsIdentifiedByUuid
{
protected static function bootIsIdentifiedByUuid()
{
static::creating(fn ($model) => static::isIdentifiedByUuidCreatingHandler($model));
static::saving(fn ($model) => static::isIdentifiedByUuidSavingHandler($model));
}
public function initializeIsIdentifiedByUuid()
{
$this->keyType = 'string';
}
protected function getUuidColumn(): string
{
return property_exists($this, 'uuid_column') ? $this->uuid_column : 'id';
}
protected static function getNewUuid(): UuidInterface
{
$columnName = app(static::class)->getUuidColumn();
$tableName = app(static::class)->getTable();
$columnDescriptor = "$tableName.$columnName";
$uuid = "";
$query = \DB::table($tableName)
->select($columnDescriptor)
->where($columnDescriptor, $uuid);
$attempts = 0;
do {
if ($attempts >= \App\Constants\Uuid::MAX_ATTEMPTS) {
throw new UuidMaxGeneratorAttemptsExceededException();
}
$uuid = Str::uuid();
$attempts++;
} while ($query->setBindings([ $uuid->toString() ])->count() > 0);
return $uuid;
}
/**
* Handles the creation of a model.
* - Generates new UUID if the UUID column is empty and auto-increment is enabled
*
* #param Model $model
* #throws \App\Exceptions\UuidMaxGeneratorAttemptsExceededException
*/
protected static function isIdentifiedByUuidCreatingHandler(Model $model)
{
$columnName = $model->getUuidColumn();
if ($model->getIncrementing() && !$model->{$columnName}) {
$uuid = static::getNewUuid();
\Log::debug(
"IsIdentifiedByUuid [CREATING]:" .
" Generating new UUID for `" . get_class($model) . ": $uuid`"
);
$model->{$columnName} = $uuid->toString();
} else {
\Log::debug(
"IsIdentifiedByUuid [CREATING]:" .
" Using existing UUID for `" . get_class($model) . ": $model->{$columnName}`"
);
}
}
/**
* Handles the saving of a Model.
* - Prevents changes to the UUID column
* - Rolls back changed value to old value
*
* #param Model $model
*/
protected static function isIdentifiedByUuidSavingHandler(Model $model)
{
$columnName = $model->getUuidColumn();
$originalUuid = $model->getOriginal($columnName);
if (!is_null($originalUuid) &&
$originalUuid !== $model->{$columnName}
) {
\Log::debug(
"IsIdentifiedByUuid [SAVING]:" .
" Prevented change of UUID for `" . get_class($model) . ":$originalUuid`"
);
$model->{$columnName} = $originalUuid;
}
}
}
Now the Problem:
Within an user-observer on the created hook I'm doing this:
$userTimeAccount = $user->timeAccount()->create([
// snip...
]);
So far - before switching to UUID instead of integer keys - everything worked fine! As far as I know creating the related model before the user-model has been saved (and obviously before auto-inc was triggered) is something that is explicitly allowed by eloquent/Laravel (though I can not find the section of the docs).
After switching to UUID this is not working anymore and I'm getting an SQL error:
SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (laravel_torus.time_accounts, CONSTRAINT time_accounts_user_id_foreign FOREIGN KEY (user_id) REFERENCES users (id)) (SQL: insert into time_accounts (time_account_type_id, balance, borrow, user_id, id, updated_at, created_at) values (3, 0, 0, 0, a995807b-b7e1-4af3-96de-7c48187f943d, 2021-07-09 12:54:25, 2021-07-09 12:54:25))
SQL beautified:
insert into `time_accounts`
(`time_account_type_id`, `balance`, `borrow`, `user_id`, `id`, `updated_at`, `created_at`)
values
(3, 0, 0, 0, 'bad86e70-7496-4b42-b2a1-5cc3c5a4d06c', '2021-07-09 11:19:17', '2021-07-09 11:19:17');
Somehow Laravel tries to insert zero (integer) for the Foreign key which will obviously not work. I even tried setting keyType to 'string' manually without effect.
Where am I wrong?
EDIT: It seems like there is a race condition. The created hook of the Observer will be triggered before the created hook of the User model. This leads to the missing ID - the ID is present when using integer and auto increment, just as it should.

Answer 1

TL;DR
I was not able to solve this with MySQL and switched to Postgres SQL.
DONT USE UUID WITH MYSQL unless you are, absolutely sure that: 1. you need to and 2. the performance impact will be negligible!
I really can not explain how this error is happening at all. The ID in question already exists (looking with the debugger into the $attribnutes array of the model), still Laravel will return integer 0 when calling $user->id.
While investigating the problem I noticed that Laravel is creating String columns for the UUID instead of binary (wich is what I would have expected). Since string comparism is quite cost intensive compared to integer/binary comparism I decided to abandon MySQL. UUID's are mandatory for this project and a shift to another DBMS, away from MySQL, in future was already intended.
Postgres SQL supports a special Column type uuid wich will be used by Laravel if a UUID column is defined. This does not only store and compare the ID as binary but also checks for format and unique values, meaning you can not enter an invalid UUID by accident like in MySQL regular sting columns wich seem to have no checks at all apart from not null and unique.