ReverseScannableDataInterface

[kamarton]

What steps will reproduce the problem?

There may be times when data needs to be scanned as reversed. Currently there is no specific interface defined, but can using with reversed Sort orders.

• RDBMS: supported partially or with sort
• NoSQL:
  • mongoDb: supported by sort
  • Apache HBase: supported by scanner level
  • Google Bigtable: not supported

What is the expected result?

$reader->withReverseScanning()->read();

condition of data reader	result
if supported it, or partially supported	scanning in reverse mode
if not supported it, but supported sorting	reverses sorting immediately before scanning
If not supported it	throw exception, or implement it at PHP level after reading the data, if possible.

examples:

• if supported it or partially supported

SELECT * FROM (
    SELECT *
    FROM ...
    WHERE id > :first
    ORDER BY id DESC
) ORDER BY id ASC LIMIT 3  -- this is not real reverse scanning

• if not supported it, but supported sorting
  exmaple in IteratorDataReader
• If not supported it
  Depending on the number of data, use the array_reverse() function, but for example, if the number of data can be hundreds of millions, can decide to throw an exception based on the withLimit(). (typically with noSQL)

What do you get instead?

data/src/Paginator/KeysetPaginator.php

Lines 70 to 75 in 992a8bc

	// reverse sorting
	foreach ($order as &$sorting) {
	$sorting = $sorting === 'asc' ? 'desc' : 'asc';
	}
	unset($sorting);
	$dataReader = $dataReader->withSort($sort->withOrder($order));

Additional info

Also consider giving Sort awithInversed() or withReverseSorting() method.

Q	A
Version	1.0.0 under development
PHP version	-
Operating system	-

[samdark]

What's the practical use case for it? Is it going to be required in paginators?

[kamarton]

Yes, she came up with the Paginator. Unnecessary abstraction. I thought the DataReader layer is easier to handle reverse scanning if this is supported or not.