From 2c8cd20b9529c37a3109bafef3efd0ff049f3ab4 Mon Sep 17 00:00:00 2001
From: Guy Sartorelli <guy.sartorelli@silverstripe.com>
Date: Thu, 21 Sep 2023 15:54:35 +1200
Subject: [PATCH] ENH Enable allowing collisions for field statements

---
 src/ORM/DataQuery.php           | 32 +++++++++++++++++++++++++++++++-
 tests/php/ORM/DataQueryTest.php | 27 +++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/src/ORM/DataQuery.php b/src/ORM/DataQuery.php
index b37f1669938..dc022bf97d0 100644
--- a/src/ORM/DataQuery.php
+++ b/src/ORM/DataQuery.php
@@ -49,6 +49,11 @@ class DataQuery
      */
     protected $collidingFields = [];
 
+    /**
+     * If true, collisions are allowed for statements aliased as db columns
+     */
+    private $allowCollidingFieldStatements = false;
+
     /**
      * Allows custom callback to be registered before getFinalisedQuery is called.
      *
@@ -287,6 +292,7 @@ public function getFinalisedQuery($queriedColumns = null)
         if ($this->collidingFields) {
             foreach ($this->collidingFields as $collisionField => $collisions) {
                 $caseClauses = [];
+                $lastClauses = [];
                 foreach ($collisions as $collision) {
                     if (preg_match('/^"(?<table>[^"]+)"\./', $collision ?? '', $matches)) {
                         $collisionTable = $matches['table'];
@@ -298,9 +304,14 @@ public function getFinalisedQuery($queriedColumns = null)
                             $caseClauses[] = "WHEN {$collisionClassColumn} IN ({$collisionClassesSQL}) THEN $collision";
                         }
                     } else {
-                        user_error("Bad collision item '$collision'", E_USER_WARNING);
+                        if ($this->getAllowCollidingFieldStatements()) {
+                            $lastClauses[] = "WHEN $collision IS NOT NULL THEN $collision";
+                        } else {
+                            user_error("Bad collision item '$collision'", E_USER_WARNING);
+                        }
                     }
                 }
+                $caseClauses = array_merge($caseClauses, $lastClauses);
                 $query->selectField("CASE " . implode(" ", $caseClauses) . " ELSE NULL END", $collisionField);
             }
         }
@@ -1358,6 +1369,25 @@ public function pushQueryManipulator(DataQueryManipulator $manipulator)
         return $this;
     }
 
+    /**
+     * Get whether field statements aliased as columns are allowed when that column is already
+     * being selected
+     */
+    public function getAllowCollidingFieldStatements(): bool
+    {
+        return $this->allowCollidingFieldStatements;
+    }
+
+    /**
+     * Set whether field statements aliased as columns are allowed when that column is already
+     * being selected
+     */
+    public function setAllowCollidingFieldStatements(bool $value): static
+    {
+        $this->allowCollidingFieldStatements = $value;
+        return $this;
+    }
+
     private function validateColumnField($field, SQLSelect $query)
     {
         // standard column - nothing to process here
diff --git a/tests/php/ORM/DataQueryTest.php b/tests/php/ORM/DataQueryTest.php
index 34ae7619d6b..9b4a835f3c8 100644
--- a/tests/php/ORM/DataQueryTest.php
+++ b/tests/php/ORM/DataQueryTest.php
@@ -172,6 +172,33 @@ public function testRelationOrderWithCustomJoin()
         $this->assertTrue(true);
     }
 
+    public function provideFieldCollision()
+    {
+        return [
+            'allow collisions' => [true],
+            'disallow collisions' => [false],
+        ];
+    }
+
+    /**
+     * @dataProvider provideFieldCollision
+     */
+    public function testFieldCollision($allowCollisions)
+    {
+        $dataQuery = new DataQuery(DataQueryTest\ObjectB::class);
+        $dataQuery->selectField('COALESCE(NULL, 1) AS "Title"');
+        $dataQuery->setAllowCollidingFieldStatements($allowCollisions);
+
+        if ($allowCollisions) {
+            $this->assertSQLContains('THEN "DataQueryTest_B"."Title" WHEN COALESCE(NULL, 1) AS "Title" IS NOT NULL THEN COALESCE(NULL, 1) AS "Title" ELSE NULL END AS "Title"', $dataQuery->sql());
+        } else {
+            $this->expectError();
+            $this->expectErrorMessageMatches('/^Bad collision item /');
+        }
+
+        $dataQuery->getFinalisedQuery();
+    }
+
     public function testDisjunctiveGroup()
     {
         $dq = new DataQuery(DataQueryTest\ObjectA::class);