Fix un-aliased query in Marshaller

The query used to find possibly existing entities should include the
table alias to avoid ambiguous column names.

Refs #8463

src/ORM/Marshaller.php

@@ -591,7 +591,8 @@ public function mergeMany($entities, array $data, array $options = [])
                 return count(array_filter($keys, 'strlen')) === count($primary);
             })
             ->reduce(function ($query, $keys) use ($primary) {
-                return $query->orWhere($query->newExpr()->and_(array_combine($primary, $keys)));
+                $fields = array_map([$this->_table, 'aliasField'], $primary);
+                return $query->orWhere($query->newExpr()->and_(array_combine($fields, $keys)));
             }, $this->_table->find());
 
         if (!empty($indexed) && count($maybeExistentQuery->clause('where'))) {

tests/TestCase/ORM/MarshallerTest.php

@@ -2150,6 +2150,30 @@ public function testMergeManyCompositeKey()
         $this->assertSame($entities[1], $result[1], 'Should retain object');
     }
 
+    /**
+     * Test mergeMany() with forced contain to ensure aliases are used in queries.
+     *
+     * @return void
+     */
+    public function testMergeManyExistingQueryAliases()
+    {
+        $entities = [
+            new OpenEntity(['id' => 1, 'comment' => 'First post', 'user_id' => 2], ['markClean' => true]),
+        ];
+
+        $data = [
+            ['id' => 1, 'comment' => 'Changed 1', 'user_id' => 1],
+            ['id' => 2, 'comment' => 'Changed 2', 'user_id' => 2],
+        ];
+        $this->comments->eventManager()->on('Model.beforeFind', function ($event, $query) {
+            return $query->contain(['Articles']);
+        });
+        $marshall = new Marshaller($this->comments);
+        $result = $marshall->mergeMany($entities, $data);
+
+        $this->assertSame($entities[0], $result[0]);
+    }
+
     /**
      * Test mergeMany() when the exist check returns nothing.
      *