FIX Ensure consistent behaviour with repeat iterations

src/ORM/Connect/MySQLQuery.php

@@ -63,6 +63,11 @@ class MySQLQuery extends Query
                 }
                 yield $data;
             }
+            // Check for the method first since $this->handle is a mixed type
+            if (method_exists($this->handle, 'data_seek')) {
+                // Reset so the query can be iterated over again
+                $this->handle->data_seek(0);
+            }
         }
     }
 

tests/php/ORM/DataListTest.php

@@ -42,7 +42,6 @@ class DataListTest extends SapphireTest
         );
     }
 
-
     public function testFilterDataObjectByCreatedDate()
     {
         // create an object to test with

tests/php/ORM/DatabaseTest.php

@@ -7,6 +7,7 @@ use SilverStripe\ORM\Connect\MySQLDatabase;
 use SilverStripe\MSSQL\MSSQLDatabase;
 use SilverStripe\Dev\SapphireTest;
 use Exception;
+use SilverStripe\ORM\Queries\SQLSelect;
 use SilverStripe\ORM\Tests\DatabaseTest\MyObject;
 
 /**
@@ -293,4 +294,58 @@ class DatabaseTest extends SapphireTest
         $this->assertEquals($inputData, $query->map());
         $this->assertEquals($inputData, $query->map());
     }
+
+    /**
+     * Test that repeated abstracted iteration of a query returns all records.
+     */
+    public function testRepeatedIterationUsingAbstraction()
+    {
+        $inputData = ['one', 'two', 'three', 'four'];
+
+        foreach ($inputData as $i => $text) {
+            $x = new MyObject();
+            $x->MyField = $text;
+            $x->MyInt = $i;
+            $x->write();
+        }
+
+        $select = SQLSelect::create(['"MyInt"', '"MyField"'], '"DatabaseTest_MyObject"', orderby: ['"MyInt"']);
+
+        $this->assertEquals($inputData, $select->execute()->map());
+        $this->assertEquals($inputData, $select->execute()->map());
+    }
+
+    /**
+     * Test that stopping iteration part-way through produces predictable results
+     * on a subsequent iteration.
+     * This test is here to ensure consistency between implementations (e.g. mysql vs postgres, etc)
+     */
+    public function testRepeatedPartialIteration()
+    {
+        $inputData = ['one', 'two', 'three', 'four'];
+
+        foreach ($inputData as $i => $text) {
+            $x = new MyObject();
+            $x->MyField = $text;
+            $x->MyInt = $i;
+            $x->write();
+        }
+
+        $query = DB::query('SELECT "MyInt", "MyField" FROM "DatabaseTest_MyObject" ORDER BY "MyInt"');
+
+        $i = 0;
+        foreach ($query as $record) {
+            $this->assertEquals($inputData[$i], $record['MyField']);
+            $i++;
+            if ($i > 1) {
+                break;
+            }
+        }
+
+        // Continue from where we left off, since we're using a Generator
+        foreach ($query as $record) {
+            $this->assertEquals($inputData[$i], $record['MyField']);
+            $i++;
+        }
+    }
 }