class Upsert

class Upsert extends QueryUpsert {
  
  /**
   * {@inheritdoc}
   */
  public function execute() {
    if (!$this->preExecute()) {
      return NULL;
    }
    // Default options for upsert queries.
    $this->queryOptions += [
      'throw_exception' => TRUE,
    ];
    // Default fields are always placed first for consistency.
    $insert_fields = array_merge($this->defaultFields, $this->insertFields);
    $table = $this->connection
      ->escapeTable($this->table);
    // We have to execute multiple queries, therefore we wrap everything in a
    // transaction so that it is atomic where possible.
    $transaction = $this->connection
      ->startTransaction();
    try {
      // First, lock the table we're upserting into.
      $this->connection
        ->query('LOCK TABLE {' . $table . '} IN SHARE ROW EXCLUSIVE MODE', [], $this->queryOptions);
      // Second, delete all items first so we can do one insert.
      $unique_key_position = array_search($this->key, $insert_fields);
      $delete_ids = [];
      foreach ($this->insertValues as $insert_values) {
        $delete_ids[] = $insert_values[$unique_key_position];
      }
      // Delete in chunks when a large array is passed.
      foreach (array_chunk($delete_ids, 1000) as $delete_ids_chunk) {
        $this->connection
          ->delete($this->table, $this->queryOptions)
          ->condition($this->key, $delete_ids_chunk, 'IN')
          ->execute();
      }
      // Third, insert all the values.
      $insert = $this->connection
        ->insert($this->table, $this->queryOptions)
        ->fields($insert_fields);
      foreach ($this->insertValues as $insert_values) {
        $insert->values($insert_values);
      }
      $insert->execute();
    } catch (\Exception $e) {
      // One of the queries failed, rollback the whole batch.
      $transaction->rollBack();
      // Rethrow the exception for the calling code.
      throw $e;
    }
    // Re-initialize the values array so that we can re-use this query.
    $this->insertValues = [];
    // Transaction commits here where $transaction looses scope.
    return TRUE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function __toString() {
    // Nothing to do.
  }

}