Issue #3154558 by heddn, catch, phjou: 1116 Too many tables; MariaDB can only...

  public function buildForm(array $form, FormStateInterface $form_state, PrivateMessageThreadInterface $privateMessageThread = NULL) {

    $form = parent::buildForm($form, $form_state);

    if ($privateMessageThread) {

      $form_state->set('thread_members', $privateMessageThread->getMembers());

      $form_state->set('thread', $privateMessageThread);

      $form['actions']['submit']['#ajax'] = [

        'callback' => '::ajaxCallback',

      ];

  public function save(array $form, FormStateInterface $formState) {

    $status = parent::save($form, $formState);

    $members = $formState->get('thread_members');

    if (!$members) {

    /** @var \Drupal\private_message\Entity\PrivateMessageThreadInterface $private_message_thread */

    $private_message_thread = $formState->get('thread');

    if (!$private_message_thread) {

      // Generate an array containing the members of the thread.

      $current_user = $this->userManager->load($this->currentUser->id());

          $members[] = $user;

        }

      }

    }

      // Get a private message thread containing the given users.

      $private_message_thread = $this->privateMessageService->getThreadForMembers($members);

    }

    // Save the thread.

    $this->privateMessageThreadManager->saveThread($this->entity, $members, [], $private_message_thread);

    $this->privateMessageThreadManager->saveThread($this->entity, $private_message_thread->getMembers(), [], $private_message_thread);

    // Save the thread to the form state.

    $formState->set('private_message_thread', $private_message_thread);

  public function getThreadIdForMembers(array $members) {

    $uids = [];

    foreach ($members as $member) {

      $uids[] = $member->id();

      $uids[$member->id()] = $member->id();

    }

    $query = $this->database->select('private_message_threads', 'pm')

      ->fields('pm', ['id'])

      ->range(0, 1);

    // First do an inner join for each user, to ensure that the user exists in

    // the thread.

    $i = 0;

    foreach ($uids as $uid) {

      $tmp_alias = 'member_' . $i;

      $query->join('private_message_thread__members', $tmp_alias, $tmp_alias . '.entity_id = pm.id AND ' . $tmp_alias . '.members_target_id = :uid' . $i, [':uid' . $i => $uid]);

      $i++;

    // There is quite possibly a cleaner way to do this entirely in SQL, but

    // the previous method using JOINs hit a system join limit in MySQL.

    $query = $this->database->select('private_message_thread__members', 'pmt')

      ->fields('pmt', ['entity_id', 'members_target_id'])

      ->condition('members_target_id', $uids, 'IN')

      ->groupBy('entity_id')

      ->groupBy('members_target_id')

      ->orderBy('entity_id', 'ASC');

    $threads = [];

    foreach ($query->execute()->fetchAll() as $result) {

      $threads[$result->entity_id] = isset($threads[$result->entity_id]) ? ++$threads[$result->entity_id] : 1;

    }

    // Next, do a left join for all rows that don't contain the users, and

    // ensure that there aren't any additional users in selected threads.

    $alias = $query->leftJoin('private_message_thread__members', 'thread_member', 'thread_member.entity_id = pm.id AND thread_member.members_target_id NOT IN (:uids[])', [':uids[]' => $uids]);

    $query->isNull($alias . '.members_target_id');

    return $query->execute()->fetchField();

    $threads = array_flip($threads);

    return $threads[count($uids)];

  }

  /**