[2.0] Fixed issue with missing parenthesis in Math expressions

lib/Doctrine/ORM/Query/Expr/Math.php

@@ -45,6 +45,20 @@ class Math
 
     public function __toString()
     {
-        return $this->_leftExpr . ' ' . $this->_operator . ' ' . $this->_rightExpr;
+        // Adjusting Left Expression
+        $leftExpr = (string) $this->_leftExpr;
+        
+        if ($this->_leftExpr instanceof Math) {
+            $leftExpr = '(' . $leftExpr . ')';
+        }
+        
+        // Adjusting Right Expression
+        $rightExpr = (string) $this->_rightExpr;
+        
+        if ($this->_rightExpr instanceof Math) {
+            $rightExpr = '(' . $rightExpr . ')';
+        }
+    
+        return $leftExpr . ' ' . $this->_operator . ' ' . $rightExpr;
     }
 }
\ No newline at end of file

tests/Doctrine/Tests/ORM/Query/ExprTest.php

@@ -129,6 +129,12 @@ class ExprTest extends \Doctrine\Tests\OrmTestCase
     {
         $this->assertEquals('10 / 2', (string) Expr::quot(10, 2));
     }
+    
+    public function testScopeInArithmeticExpr()
+    {
+        $this->assertEquals('(100 - 20) / 2', (string) Expr::quot(Expr::diff(100, 20), 2));
+        $this->assertEquals('100 - (20 / 2)', (string) Expr::diff(100, Expr::quot(20, 2)));
+    }
 
     public function testSquareRootExpr()
     {