InvalidMergeQueryException example

  public function execute() {
    if (!count($this->condition)) {
      throw new InvalidMergeQueryException('Invalid merge query: no conditions');
    }

    $select = $this->connection->select($this->conditionTable)
      ->condition($this->condition);
    $select->addExpression('1');

    if (!$select->execute()->fetchField()) {
      try {
        $insert = $this->connection->insert($this->table)->fields($this->insertFields);
        if ($this->defaultFields) {
          $insert->useDefaults($this->defaultFields);
        }