#27504 fix joinprocessor behavior with consecutive calls

Author: fgerodez

dev/tests/integration/testsuite/Magento/Framework/Api/SearchCriteria/CollectionProcessor/JoinProcessorTest.php

@@ -0,0 +1,60 @@
+<?php
+declare(strict_types=1);
+
+namespace Magento\Framework\Api\SearchCriteria\CollectionProcessor;
+
+use Magento\Framework\Api\SearchCriteria\CollectionProcessor\JoinProcessor\CustomJoinInterface;
+use Magento\Framework\Api\SearchCriteriaBuilder;
+use Magento\Framework\Data\Collection\AbstractDb;
+use PHPUnit\Framework\TestCase;
+
+class JoinProcessorTest extends TestCase
+{
+    /**
+     * @var \Magento\Framework\ObjectManagerInterface
+     */
+    private $objectManager;
+
+    protected function setUp(): void
+    {
+        $this->objectManager = \Magento\TestFramework\Helper\Bootstrap::getObjectManager();
+    }
+
+    /**
+     * Test proper application of the join processor for consecutive calls with different collections.
+     *
+     * @return void
+     */
+    public function testMultipleCollections(): void
+    {
+        $customJoinMock = $this->getMockBuilder(CustomJoinInterface::class)
+            ->getMock();
+
+        $customJoinMock->expects($this->exactly(2))
+            ->method('apply');
+
+        $joinProcessor = $this->objectManager->create(JoinProcessor::class, [
+            'customJoins' => [
+                'test_join' => $customJoinMock,
+            ],
+            'fieldMapping' => [
+                'test_field' => 'test_join',
+            ],
+        ]);
+
+        $searchCriteria = $this->objectManager->create(SearchCriteriaBuilder::class)
+            ->addFilter('test_field', 'test')
+            ->create();
+
+        $collection1 = $this->getMockBuilder(AbstractDb::class)
+            ->disableOriginalConstructor()
+            ->getMockForAbstractClass();
+
+        $collection2 = $this->getMockBuilder(AbstractDb::class)
+            ->disableOriginalConstructor()
+            ->getMockForAbstractClass();
+
+        $joinProcessor->process($searchCriteria, $collection1);
+        $joinProcessor->process($searchCriteria, $collection2);
+    }
+}

lib/internal/Magento/Framework/Api/SearchCriteria/CollectionProcessor/JoinProcessor.php

@@ -72,6 +72,8 @@ public function process(SearchCriteriaInterface $searchCriteria, AbstractDb $col
                 }
             }
         }
+
+        $this->appliedFields = [];
     }
 
     /**