[4.4] Fix SQL field, get the filter value from the linked filter field (joomla#43789)

* Fix SQL field, get the filter value from the linked filter field

* cs

* esc

---------

Author: Fedik

libraries/src/Form/Field/SqlField.php

@@ -233,12 +233,21 @@ protected function processQuery($conditions, $filters, $defaults)
 
         // Process the filters
         if (\is_array($filters)) {
-            $html_filters = Factory::getApplication()->getUserStateFromRequest($this->context . '.filter', 'filter', [], 'array');
+            // @TODO: Loading the filtering value from the request need to be deprecated.
+            $html_filters = $this->context ? Factory::getApplication()->getUserStateFromRequest($this->context . '.filter', 'filter', [], 'array') : false;
+            $form         = $this->form;
 
             foreach ($filters as $k => $value) {
-                if (!empty($html_filters[$value])) {
+                // Get the filter value from the linked filter field
+                $filterFieldValue = $form->getValue($value, $this->group);
+
+                if ($html_filters && !empty($html_filters[$value])) {
                     $escape = $db->quote($db->escape($html_filters[$value]), false);
 
+                    $query->where("{$value} = {$escape}");
+                } elseif ($filterFieldValue !== null) {
+                    $escape = $db->quote($db->escape($filterFieldValue), false);
+
                     $query->where("{$value} = {$escape}");
                 } elseif (!empty($defaults[$value])) {
                     $escape = $db->quote($db->escape($defaults[$value]), false);