Query: Relative path fallback for createSubQuery

src/Query.php

@@ -701,6 +701,17 @@ public function createSubQuery(Model $target, string $targetPath, ?Model $from =
             ->setDb($this->getDb())
             ->setModel($target);
 
+        if (! str_starts_with($targetPath, $this->getModel()->getTableAlias() . '.')) {
+            trigger_error(sprintf(
+                'Target path "%s" does not start with the source model\'s table alias "%s".'
+                . ' This is deprecated and will be removed in a future version. Use "%s" as target path instead.',
+                $targetPath,
+                $this->getModel()->getTableAlias(),
+                $this->getModel()->getTableAlias() . '.' . $targetPath
+            ), E_USER_DEPRECATED);
+            $targetPath = $this->getModel()->getTableAlias() . '.' . $targetPath;
+        }
+
         $subQueryResolver = $subQuery->getResolver();
 
         $forwardHops = array_slice(explode('.', $targetPath), 0, -1);

tests/QueryTest.php

@@ -622,6 +622,31 @@ public function testUnreferencedTargetCanBePassedToCreateSubQuery(): void
         $this->assertInstanceOf(Query::class, $query);
     }
 
+    public function testCreateSubQueryAcceptsRelativeTargetPaths(): void
+    {
+        $deprecations = [];
+        set_error_handler(function ($_, $message) use (&$deprecations) {
+            $deprecations[] = $message;
+
+            return true;
+        }, E_USER_DEPRECATED);
+
+        try {
+            $query = Profile::on(new TestConnection())
+                ->createSubQuery(new User(), 'user');
+        } finally {
+            restore_error_handler();
+        }
+
+        $this->assertNotEmpty($deprecations, 'createSubQuery did not emit a deprecation');
+        $this->assertStringContainsString(
+            'Target path "user" does not start with the source model\'s table alias "profile".',
+            $deprecations[0]
+        );
+
+        $this->assertInstanceOf(Query::class, $query);
+    }
+
     public function testDeriveLetsTheBaseModelBeReferencedAsSelfInFilters(): void
     {
         $user = new User(['id' => 1, 'username' => 'test']);