Use generators over iterators so can easily reuse fetch methods.

lib/Doctrine/DBAL/Driver/AbstractIterator.php

-<?php
-
-namespace Doctrine\DBAL\Driver;
-
-abstract class AbstractIterator
-{
-    protected $cursor;
-    protected $key;
-    protected $current;
-    protected $fetched = 0;
-    protected $defaultFetchMode;
-
-    public function __construct($cursor, $defaultFetchMode = \PDO::FETCH_BOTH)
-    {
-        $this->cursor = $cursor;
-        $this->defaultFetchMode = $defaultFetchMode;
-        $this->next();
-    }
-
-    public function current()
-    {
-        return $this->current;
-    }
-
-    public function next()
-    {
-        $this->key = $this->fetched;
-        $this->current = $this->fetch();
-
-        if ($this->current) {
-            $this->fetched++;
-        }
-    }
-
-    public function key()
-    {
-        return $this->key;
-    }
-
-    public function valid()
-    {
-        return (bool)$this->current;
-    }
-
-    public function rewind()
-    {
-        // Not supported
-    }
-
-    abstract protected function fetch();
-}

lib/Doctrine/DBAL/Driver/IBMDB2/DB2Iterator.php

-<?php
-
-namespace Doctrine\DBAL\Driver\IBMDB2;
-
-use Doctrine\DBAL\Driver\AbstractIterator;
-
-class DB2Iterator extends AbstractIterator implements \Iterator
-{
-    protected function fetch()
-    {
-        switch ($this->defaultFetchMode) {
-            case \PDO::FETCH_BOTH:
-                return db2_fetch_both($this->cursor);
-            case \PDO::FETCH_ASSOC:
-                return db2_fetch_assoc($this->cursor);
-            case \PDO::FETCH_CLASS:
-                return db2_fetch_object($this->cursor);
-            case \PDO::FETCH_NUM:
-                return db2_fetch_array($this->cursor);
-            case \PDO::FETCH_OBJ:
-                return db2_fetch_object($this->cursor);
-            default:
-                throw new DB2Exception("Given Fetch-Style " . $this->defaultFetchMode . " is not supported.");
-        }
-    }
-}

lib/Doctrine/DBAL/Driver/IBMDB2/DB2Statement.php

@@ -199,7 +199,9 @@ class DB2Statement implements \IteratorAggregate, Statement
      */
     public function getIterator()
     {
-        return new DB2Iterator($this->_stmt, $this->_defaultFetchMode);
+        while ($row = $this->fetch()) {
+            yield $row;
+        }
     }
 
     /**

lib/Doctrine/DBAL/Driver/Mysqli/MysqliStatement.php

@@ -406,8 +406,8 @@ class MysqliStatement implements \IteratorAggregate, Statement
      */
     public function getIterator()
     {
-        $data = $this->fetchAll();
-
-        return new \ArrayIterator($data);
+        while ($row = $this->fetch()) {
+            yield $row;
+        }
     }
 }

lib/Doctrine/DBAL/Driver/OCI8/OCI8Iterator.php

-<?php
-
-namespace Doctrine\DBAL\Driver\OCI8;
-
-use Doctrine\DBAL\Driver\AbstractIterator;
-
-class OCI8Iterator extends AbstractIterator implements \Iterator
-{
-    private static $fetchModeMap = array(
-        \PDO::FETCH_BOTH => OCI_BOTH,
-        \PDO::FETCH_ASSOC => OCI_ASSOC,
-        \PDO::FETCH_NUM => OCI_NUM,
-        \PDO::FETCH_COLUMN => OCI_NUM,
-    );
-
-    protected function fetch()
-    {
-        $result = [];
-
-        if (\PDO::FETCH_OBJ === $this->defaultFetchMode) {
-            return oci_fetch_object($this->cursor);
-        }
-
-        if (self::$fetchModeMap[$this->defaultFetchMode] === OCI_BOTH) {
-            return oci_fetch_array(
-                $this->cursor,
-                $this->defaultFetchMode | OCI_RETURN_NULLS | OCI_RETURN_LOBS
-            );
-        }
-
-        $fetchStructure = OCI_FETCHSTATEMENT_BY_ROW;
-        if ($this->defaultFetchMode === \PDO::FETCH_COLUMN) {
-            $fetchStructure = OCI_FETCHSTATEMENT_BY_COLUMN;
-        }
-
-        oci_fetch_all(
-            $this->cursor,
-            $result,
-            0,
-            -1,
-            self::$fetchModeMap[$this->defaultFetchMode] | OCI_RETURN_NULLS | $fetchStructure | OCI_RETURN_LOBS
-        );
-
-        return $result;
-    }
-}

lib/Doctrine/DBAL/Driver/OCI8/OCI8Statement.php

@@ -370,7 +370,9 @@ class OCI8Statement implements IteratorAggregate, Statement
      */
     public function getIterator()
     {
-        return new OCI8Iterator($this->_sth, $this->_defaultFetchMode);
+        while ($row = $this->fetch()) {
+            yield $row;
+        }
     }
 
     /**

lib/Doctrine/DBAL/Driver/SQLAnywhere/SQLAnywhereIterator.php

-<?php
-
-namespace Doctrine\DBAL\Driver\SQLAnywhere;
-
-use Doctrine\DBAL\Driver\AbstractIterator;
-
-class SQLAnywhereIterator extends AbstractIterator implements \Iterator
-{
-    protected function fetch()
-    {
-        $result = sasql_stmt_result_metadata($this->cursor);
-
-        switch ($this->defaultFetchMode) {
-            case \PDO::FETCH_ASSOC:
-                return sasql_fetch_assoc($this->cursor);
-            case \PDO::FETCH_BOTH:
-                return sasql_fetch_array($result, SASQL_BOTH);
-            case \PDO::FETCH_CLASS:
-                return sasql_fetch_object($result);
-            case \PDO::FETCH_NUM:
-                return sasql_fetch_row($result);
-            case \PDO::FETCH_OBJ:
-                return sasql_fetch_object($result);
-            default:
-                throw new SQLAnywhereException('Fetch mode is not supported: ' . $this->defaultFetchMode);
-        }
-    }
-}

lib/Doctrine/DBAL/Driver/SQLAnywhere/SQLAnywhereStatement.php

@@ -278,7 +278,9 @@ class SQLAnywhereStatement implements IteratorAggregate, Statement
      */
     public function getIterator()
     {
-        return new SQLAnywhereIterator($this->stmt, $this->defaultFetchMode);
+        while ($row = $this->fetch()) {
+            yield $row;
+        }
     }
 
     /**

lib/Doctrine/DBAL/Driver/SQLSrv/SQLSrvIterator.php

-<?php
-
-namespace Doctrine\DBAL\Driver\SQLSrv;
-
-use Doctrine\DBAL\Driver\AbstractIterator;
-
-class SQLSrvIterator extends AbstractIterator implements \Iterator
-{
-    protected function fetch()
-    {
-        return sqlsrv_fetch_array($this->cursor, $this->defaultFetchMode);
-    }
-}

lib/Doctrine/DBAL/Driver/SQLSrv/SQLSrvStatement.php

@@ -295,7 +295,9 @@ class SQLSrvStatement implements IteratorAggregate, Statement
      */
     public function getIterator()
     {
-        return new SQLSrvIterator($this->stmt, $this->defaultFetchMode);
+        while ($row = $this->fetch()) {
+            yield $row;
+        }
     }
 
     /**