FIX: Sorting a DataQuery over a relation.

When sorting a DataQuery over a relation, the SQLQuery automatically included the sort column. The issue with the implement is that potentially the joined record has a field with the same name as the source record causing it to be overridden.

In the attached test case, without the patch the title will be set to 'Bar' rather than 'Foo'.

This patch aliases the sort column. Alternativally a patch would be to

model/DataQuery.php

@@ -256,6 +256,7 @@ protected function ensureSelectContainsOrderbyColumns($query, $originalSelect =
 
 		if($orderby = $query->getOrderBy()) {
 			$newOrderby = array();
+			$i = 0;
 			foreach($orderby as $k => $dir) {
 				$newOrderby[$k] = $dir;
 
@@ -268,7 +269,10 @@ protected function ensureSelectContainsOrderbyColumns($query, $originalSelect =
 
 				// Pull through SortColumn references from the originalSelect variables
 				if(preg_match('/_SortColumn/', $col)) {
-					if(isset($originalSelect[$col])) $query->selectField($originalSelect[$col], $col);
+					if(isset($originalSelect[$col])) {
+						$query->selectField($originalSelect[$col], $col);
+					}
+
 					continue;
 				}
 
@@ -287,6 +291,7 @@ protected function ensureSelectContainsOrderbyColumns($query, $originalSelect =
 
 					// remove original sort
 					unset($newOrderby[$k]);
+
 					// add new columns sort
 					$newOrderby[$qualCol] = $dir;
 
@@ -298,13 +303,17 @@ protected function ensureSelectContainsOrderbyColumns($query, $originalSelect =
 					}
 				} else {
 					$qualCol = '"' . implode('"."', $parts) . '"';
-
-					// To-do: Remove this if block once SQLQuery::$select has been refactored to store getSelect()
-					// format internally; then this check can be part of selectField()
+
 					if(!in_array($qualCol, $query->getSelect())) {
-						$query->selectField($qualCol);
+						unset($newOrderby[$k]);
+
+						$newOrderby["\"_SortColumn$i\""] = $dir;
+						$query->selectField($qualCol, "_SortColumn$i");
+
+						$i++;
 					}
 				}
+
 			}
 
 			$query->setOrderBy($newOrderby);

tests/model/DataQueryTest.php

@@ -12,6 +12,27 @@ class DataQueryTest extends SapphireTest {
 		'DataQueryTest_E',
 	);
 
+
+	public function testSortByJoinedFieldRetainsSourceInformation() {
+		$bar = new DataQueryTest_C();
+		$bar->Title = "Bar";
+		$bar->write();
+
+		$foo = new DataQueryTest_B();
+		$foo->Title = "Foo";
+		$foo->TestC = $bar->ID;
+		$foo->write();
+
+		$query = new DataQuery('DataQueryTest_B');
+		$result = $query->leftJoin(
+			'DataQueryTest_C',
+			"\"DataQueryTest_B\".\"TestCID\" = \"DataQueryTest_B\".\"ID\""
+		)->sort('"DataQueryTest_B"."Title"', 'ASC');
+
+		$result = $result->execute()->record();
+		$this->assertEquals('Foo', $result['Title']);
+	}
+
 	/**
 	 * Test the leftJoin() and innerJoin method of the DataQuery object
 	 */
@@ -138,6 +159,7 @@ public function testDefaultSort() {
 
 
 class DataQueryTest_A extends DataObject implements TestOnly {
+
 	private static $db = array(
 		'Name' => 'Varchar',
 	);
@@ -147,7 +169,8 @@ class DataQueryTest_A extends DataObject implements TestOnly {
 	);
 }
 
-class DataQueryTest_B extends DataQueryTest_A {
+class DataQueryTest_B extends DataObject implements TestOnly {
+
 	private static $db = array(
 		'Title' => 'Varchar',
 	);