ENGCOM-3086: Fix/add expresion #17915

Author: nmalevanec

lib/internal/Magento/Framework/Model/ResourceModel/Db/Collection/AbstractCollection.php

@@ -45,6 +45,13 @@ abstract class AbstractCollection extends AbstractDb implements SourceProviderIn
      */
     protected $_fieldsToSelect = null;
 
+    /**
+     * Expression fields to select in query.
+     *
+     * @var array
+     */
+    private $expressionFieldsToSelect = [];
+
     /**
      * Fields initial fields to select like id_field
      *
@@ -205,7 +212,7 @@ protected function _initSelectFields()
         $columnsToSelect = [];
         foreach ($columns as $columnEntry) {
             list($correlationName, $column, $alias) = $columnEntry;
-            if ($correlationName !== 'main_table') {
+            if ($correlationName !== 'main_table' || isset($this->expressionFieldsToSelect[$alias])) {
                 // Add joined fields to select
                 if ($column instanceof \Zend_Db_Expr) {
                     $column = $column->__toString();
@@ -346,9 +353,8 @@ public function addExpressionFieldToSelect($alias, $expression, $fields)
             $fullExpression = str_replace('{{' . $fieldKey . '}}', $fieldItem, $fullExpression);
         }
 
-        $fullExpression = new \Zend_Db_Expr($fullExpression);
-        $this->_fieldsToSelect[$alias] = $fullExpression;
-        $this->_fieldsToSelectChanged = true;
+        $this->getSelect()->columns([$alias => $fullExpression]);
+        $this->expressionFieldsToSelect[$alias] = $fullExpression;
 
         return $this;
     }

lib/internal/Magento/Framework/Model/Test/Unit/ResourceModel/Db/Collection/AbstractCollectionTest.php

@@ -269,9 +269,8 @@ public function addFieldToSelectDataProvider()
      */
     public function testAddExpressionFieldToSelect($alias, $expression, $fields, $expected)
     {
+        $this->selectMock->expects($this->once())->method('columns')->with($expected);
         $this->assertTrue($this->uut->addExpressionFieldToSelect($alias, $expression, $fields) instanceof Uut);
-        $this->assertEquals($expected, $this->uut->getFieldsToSelect());
-        $this->assertTrue($this->uut->wereFieldsToSelectChanged());
     }
 
     /**