Bugfix for mid-set rewind() in PrefetchIterator (#907)

Author: thomascorthals

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Fixed
 - PrefetchIterator::key() should return 0 instead of NULL on a fresh PrefetchIterator
 - PrefetchIterator::next() shouldn't skip fetched results after PrefetchIterator::count() on a fresh PrefetchIterator
+- PrefetchIterator::rewind() no longer results in duplicate documents when invoked mid-set
 - fixed incorrect median function
 
 ### Changed

src/Plugin/PrefetchIterator.php

@@ -173,9 +173,12 @@ public function rewind(): void
     {
         $this->position = 0;
 
-        // this condition prevents erroneously fetching the next set of results if a count is done before the iterator is used
-        if ($this->start !== $this->options['prefetch']) {
+        // this condition prevents needlessly re-fetching if the iterator hasn't moved past its first set of results yet
+        // (this includes when a count is done before the iterator is used)
+        if ($this->start > $this->options['prefetch']) {
             $this->start = 0;
+            $this->result = null;
+            $this->documents = null;
 
             if (null !== $this->cursormark) {
                 $this->cursormark = '*';

tests/Integration/AbstractTechproductsTest.php

@@ -1887,6 +1887,44 @@ public function testPrefetchIteratorWithoutAndWithCursormark()
         $this->assertSame($without, $with);
     }
 
+    public function testPrefetchIteratorManualRewind()
+    {
+        $select = self::$client->createSelect();
+        $select->addSort('id', SelectQuery::SORT_ASC);
+        /** @var PrefetchIterator $prefetch */
+        $prefetch = self::$client->getPlugin('prefetchiterator');
+        $prefetch->setPrefetch(5);
+        $prefetch->setQuery($select);
+
+        // check if valid (this will fetch the first set of documents)
+        $this->assertTrue($prefetch->valid());
+        // check that we're at position 0
+        $this->assertSame(0, $prefetch->key());
+        // current document is the one with lowest alphabetical id in techproducts
+        $this->assertSame('0579B002', $prefetch->current()->id);
+
+        // move to an arbitrary point past the first set of fetched documents
+        while (12 > $prefetch->key()) {
+            $prefetch->next();
+            // this ensures the next set will be fetched when we've passed the end of a set
+            $this->assertTrue($prefetch->valid());
+        }
+
+        // check that we've reached the expected document at position 12
+        $this->assertSame(12, $prefetch->key());
+        $this->assertSame('NOK', $prefetch->current()->id);
+
+        // this resets the position and clears the last fetched result
+        $prefetch->rewind();
+
+        // check if valid (this will re-fetch the first set of documents)
+        $this->assertTrue($prefetch->valid());
+        // check that we're back at position 0
+        $this->assertSame(0, $prefetch->key());
+        // current document is once again the one with lowest alphabetical id in techproducts
+        $this->assertSame('0579B002', $prefetch->current()->id);
+    }
+
     public function testExtractIntoDocument()
     {
         $extract = self::$client->createExtract();