WP_Query with multiple orderby NOT working with ASC and DESC, what's wrong?

Question

I have a query with multiple orderby params in a custom page that I am having difficulty getting to work. The query is to return posts with either tag-AAA or tag-BBB tags. And I'd like to sort it based on DESC order by post_date but within the same pub day sort by post title in ASC order. I tried the following but it does not work. Whatever I set as the first argument in orderby sees to win the sort and the next appears to be not taken into account at all. Any assistance is appreciated.

$args = array(              
'tag' => 'tag-AAA,tag-BBB',     
array ('orderby' => array(   'title' => 'ASC', 'post_date' => 'DESC') ),
$query = new WP_Query($args);

Answer 1

Your code is invalid (syntax error, missing closing array and semi-colon), and incorrectly nested - if you were to properly indent your code, you'd have something like:

$args = array(              
    'tag' => 'tag-AAA,tag-BBB',     
    array (
        'orderby' => array(
            'title' => 'ASC',
            'post_date' => 'DESC',
        )
    ),
);

See how orderby isn't actually a property of $args? You need:

$args = array(              
    'tag'     => 'tag-AAA,tag-BBB', 
    'orderby' =>  array(
        'post_date' => 'DESC',
        'title'     => 'ASC',
    ),
);

I've also switched the order so that posts are ordered first by date, then by title.