Illuminate\Database\Eloquent\Relations\BelongsTo::getEagerModelKeys PHP Метод

    protected function getEagerModelKeys(array $models)
    {
        $keys = [];
        // First we need to gather all of the keys from the parent models so we know what
        // to query for via the eager loading query. We will add them to an array then
        // execute a "where in" statement to gather up all of those related records.
        foreach ($models as $model) {
            if (!is_null($value = $model->{$this->foreignKey})) {
                $keys[] = $value;
            }
        }
        // If there are no keys that were not null we will just return an array with either
        // null or 0 in (depending on if incrementing keys are in use) so the query wont
        // fail plus returns zero results, which should be what the developer expects.
        if (count($keys) === 0) {
            return [$this->related->getIncrementing() && $this->related->getKeyType() === 'int' ? 0 : null];
        }
        return array_values(array_unique($keys));
    }