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.
    }

}