How to alter view query after exposed filter is changed?

Question

We have a custom view, myview, that has two exposed filters: country and category. For the country value we have a value that we want to be applied regardless of what is selected as the exposed filter that is not All Countries.

How would we alter the query after a value is selected so that we always append an or country = United States of America to whatever value is selected for the view's query?

Goal:

After the exposed filter has been applied, alter the query such that it will return whatever the user selected AND all other nodes where country = 'United States'.

Country value:

1. All Countries
2. Worldwide
3. United States of America
4. United Kingdom
5. France
6. Germany

What we were thinking of using hook_views_query_alter, but not sure how we can alter the query after a value has been selected.

mymodule.module

use Drupal\views\ViewExecutable;
use Drupal\views\Plugin\views\query\QueryPluginBase;

/**
 * Implements hook_views_query_alter().
 */
function mymodule_views_query_alter(ViewExecutable $view, QueryPluginBase $query) {

  if ($view->id() == 'myview') {
    $or_statement = new Condition('OR');
    $or_statement->condition('field_country', '12', '=');
    $query->addWhere(0, $or_statement);
  }

}

Current filters:

1. published = yes
2. content type = article
3. country (exposed filter, display all, single select)
4. category (exposed filter, display all, single select)

When using ksm() to print the $condition_group, this is the results. It is not even showing the two exposed filters.

Current Where Clause

10 is the value selected by the user from the exposed filter and 12 is the one we want to add.

WHERE (((node__field_country.field_country_target_id = '10')) AND (node__field_country.field_country_target_id = '12'))

Desired where clause

WHERE (((node__field_country.field_country_target_id = '10')) OR (node__field_country.field_country_target_id = '12'))

Answer 1

Using d70rr3s suggestion and this patch (required), I came across this solution that worked.

use Drupal\views\ViewExecutable;
use Drupal\views\Plugin\views\query\QueryPluginBase;

/**
 * Implements hook_views_query_alter().
 */
function mymodule_views_query_alter(ViewExecutable $view, QueryPluginBase $query) {
   if ($view->id() == 'myview'  && !empty($view->exposed_raw_input['field_country']) && $view->exposed_raw_input['field_country'] !== 'all') {
    // Traverse through the 'where' part of the query.
    foreach ($query->where as &$condition_group) {
      foreach ($condition_group['conditions'] as &$condition) {
        if ($condition['field'] == 'your_entity.field_country') {
          $field = 'node__field_country.field_country_target_id';
          $value = 'somevalue';
          $operator = '=';
          $query->addWhere(2, $field, $value, $operator);
        }
      }
    }
  }
}

Results:

WHERE (((node__field_country.field_country_target_id = '10')) OR (node__field_country.field_country_target_id = 'someValue')) AND (node_field_data.status=1) AND (node_field_data.type='article')

Filter Criteria where #1 and #2 from screenshot had to be applied:

Answer 2

Taken from the hook example. Assuming your filter name is field-country a possible solution could be:

use Drupal\views\ViewExecutable;
use Drupal\views\Plugin\views\query\QueryPluginBase;

/**
 * Implements hook_views_query_alter().
 */
function mymodule_views_query_alter(ViewExecutable $view, QueryPluginBase $query) {
   if ($view->id() == 'myview'  && !empty($view->exposed_raw_input['field_country']) && $view->exposed_raw_input['field_country'] != 'all') {
    // Traverse through the 'where' part of the query.
    foreach ($query->where as &$condition_group) {
      foreach ($condition_group['conditions'] as &$condition) {
        if ($condition['field'] == 'your_entity.field_country') {
           $filter_value = $view->exposed_raw_input['field_country'];
           if (!is_array($filter_value)) {
             $filter_value = [$filter_value];
           }

           $condition = [
             'field' => 'your_entity.field_country',
             'value' => array_merge($filter_value, ['United States Of America']),
             'operator' => 'IN',
           ];
        }
      }
    }
  }
}

I haven't fully test it but should work.

Also you can always implement your own ad-hoc filter plugin.

Update: Add a condition to check if the filter is multivalue.

Update: Remove strict comparison for filter input value as it may cause side-effects.