BatchRangeIterator.php

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<?php
namespace Magento\Framework\DB\Query;

use Magento\Framework\DB\Adapter\AdapterInterface;
use Magento\Framework\DB\Select;

class BatchRangeIterator implements BatchIteratorInterface
{
    private $currentSelect;

    private $rangeField;

    private $rangeFieldAlias;

    private $batchSize;

    private $connection;

    private $currentOffset = 0;

    private $totalItemCount;

    private $iteration = 0;

    private $select;

    private $correlationName;

    private $isValid = true;

    public function __construct(
        Select $select,
        $batchSize,
        $correlationName,
        $rangeField,
        $rangeFieldAlias
    ) {
        $this->batchSize = $batchSize;
        $this->select = $select;
        $this->correlationName = $correlationName;
        $this->rangeField = $rangeField;
        $this->rangeFieldAlias = $rangeFieldAlias;
        $this->connection = $select->getConnection();
    }

    public function current()
    {
        if (null === $this->currentSelect) {
            $this->isValid = $this->currentOffset < $this->totalItemCount;
            $this->currentSelect = $this->initSelectObject();
        }
        return $this->currentSelect;
    }

    public function key()
    {
        return $this->iteration;
    }

    public function next()
    {
        if (null === $this->currentSelect) {
            $this->current();
        }
        $this->isValid = $this->currentOffset < $this->totalItemCount;
        $select = $this->initSelectObject();
        if ($this->isValid) {
            $this->iteration++;
            $this->currentSelect = $select;
        } else {
            $this->currentSelect = null;
        }
        return $this->currentSelect;
    }

    public function rewind()
    {
        $this->currentSelect = null;
        $this->iteration = 0;
        $this->isValid = true;
        $this->totalItemCount = 0;
    }

    public function valid()
    {
        return $this->isValid;
    }

    private function initSelectObject()
    {
        $object = clone $this->select;

        if (!$this->totalItemCount) {
            $wrapperSelect = $this->connection->select();
            $wrapperSelect->from(
                $object,
                [
                    new \Zend_Db_Expr('COUNT(*) as cnt')
                ]
            );
            $row = $this->connection->fetchRow($wrapperSelect);

            $this->totalItemCount = intval($row['cnt']);
        }

        $rangeField = is_array($this->rangeField) ? $this->rangeField : [$this->rangeField];

        foreach ($rangeField as $field) {
            $object->order($this->correlationName . '.' . $field . ' ' . \Magento\Framework\DB\Select::SQL_ASC);
        }
        $object->limit($this->batchSize, $this->currentOffset);
        $this->currentOffset += $this->batchSize;

        return $object;
    }
}