I have a php script on my Joomla 3 that work fine to restrict user to only send one submission, look like this:

global $database;
$rsuser = JFactory::getUser();
$id = $rsuser->get('id');
$database = JFactory::getDBO();
$database->setQuery("SELECT COUNT(`SubmissionId`) FROM dbprefix_rsform_submissions WHERE UserId=$id AND FormId='3'");
$database->query();
if (intval($database->loadResult()) >= 1)
{
echo 'Det är endast tillåtet att ladda upp en bild! Önskar du ladda upp ny bild ska du kontakta This e-mail address is being protected from spambots. You need JavaScript enabled to view it ';
$formLayout = '';
}

In joomla 4 i got this error: 0 Call to undefined method Joomla\Database\Mysqli\MysqliDriver::query()

What do I have to change to get working on Joomla 4?

Hello,

Without custom scripting, you can try using one of the following validation rules while editing the Email field:

- Unique Field: if enabled, this validation will only allow a field value that hasn't been submitted before, for that particular form.
- Unique Field per User: if enabled, this validation will only allow a field value that hasn't been submitted before by the logged in user.

More on this here.

If however you want to take a custom scripting approach, you can find various examples on adding counter for submissions here.

How about creating an INDEX in the database and applying an UNIQUE property. The database will take care od the rest.
In that index you could simply encapsulate needed fields (columns). For example: USER_ID, RESPONSE_ID this will not allow to save two records with the same use and same response