If you are using theme_get_settings, such as: $value = trim(theme_get_setting('my_setting')); Then in your code editor you will also be seeing undefined  function 'theme_get_setting'.  This function has been deprecated for some time.   Instead, you need to use Passing the theme.manager and theme.initialization services to theme_handler constructor as optional parameters is deprecated. These parameters are also mandatory. $theme_handler = \Drupal::service('theme_handler');Get...

I had the issue where I needed to filter an array list by a specific column.  In my instance, the column is language.  To be able to reduce the query to the language column the code required is levels = selectedCategory?.levels.filter("language = %@", language)Language can be any string, in this instance for me language is a two alpha character such as 'fr', 'en' or 'de'. Further to this you can continue to chain this query through including sort as per levels =...