Insert parent and child at once via Eloquent in Laravel 5.4

I am trying to insert a two related objects via Eloquent and I get an Integrity constraint violation error on one of the tables. Here is what I am trying:

The representation of the relationship:

class DataParticipant extends Model
{
    public function data_config()
    {
        return $this->hasOne('App\Models\DataConfig');
    }
}

class DataConfig extends Model
{
    public function data_participant()
    {
        return $this->belongsTo('App\Models\DataParticipant');
    }
}

Then, I am trying the following:

$dataParticipant = new DataParticipant();

$dataParticipant->ip = // ip
$dataParticipant->code = // code
$dataParticipant->study_name = // study


// Prepare the config child.

$dataConfig = new DataConfig();
$dataConfig->config = // config via json_encode 


// Store the child associated to the parent.

$dataParticipant->data_config()->save($dataConfig);

The error is on data_participant_id column, which belongs to the DataConfig model. My guess is that there is no id on which the two can be linked. I want to ask you:

• How can I accomplish this without having to first save the DataParticipant then retrieve it from the database and then store the DataConfig on the resulted id?

via Chebli Mohamed