Add rewindable generator in order fix the issue with mutliple iterations.

Only added to mysqli for now, can add to other drivers (assuming they
support reseting the pointer in some way) after feedback.

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

@@ -20,6 +20,7 @@
 namespace Doctrine\DBAL\Driver\Mysqli;
 
 use Doctrine\DBAL\Driver\Statement;
+use Doctrine\DBAL\RewindableGenerator;
 use PDO;
 
 /**
@@ -406,8 +407,11 @@ class MysqliStatement implements \IteratorAggregate, Statement
      */
     public function getIterator()
     {
-        while ($row = $this->fetch()) {
-            yield $row;
-        }
+        return new RewindableGenerator(function() {
+            $this->_stmt->data_seek(0);
+            while ($row = $this->fetch()) {
+                yield $row;
+            }
+        });
     }
 }

lib/Doctrine/DBAL/RewindableGenerator.php

+<?php
+
+namespace Doctrine\DBAL;
+
+class RewindableGenerator implements \IteratorAggregate
+{
+    private $generator;
+
+    /**
+     * @param callable $generator
+     */
+    public function __construct(callable $generator)
+    {
+        $this->generator = $generator;
+    }
+
+    public function getIterator()
+    {
+        $g = $this->generator;
+
+        return $g();
+    }
+}

tests/Doctrine/Tests/DBAL/Functional/DataAccessTest.php

@@ -879,7 +879,7 @@ class DataAccessTest extends \Doctrine\Tests\DbalFunctionalTestCase
         }
 
         $j = 0;
-        foreach ($stmt as $row) {
+        foreach ($stmt as $row2) {
             $j++;
         }