How can I apply a meta query for a single custom post type in the main query?

Question

I have custom post type called event, which has custom fields for start_date and end_date. For the event archive, I'm filtering out "expired" events using the following meta query added to the main query inside a pre_get_posts filter, which works fine:

if ( is_post_type_archive( 'event' ) ) {
    $query->set( 'meta_query', array(
        'relation' => 'OR',
        array(
            'key' => 'start_date',
            'value' => $today = date( 'Ymd' ),
            'compare' => '>='
        ),
        array(
            'key' => 'end_date',
            'value' => $today = date( 'Ymd' ),
            'compare' => '>='
        ),
    ) );
}

I'd like to do the same for search queries. Is it possible to add a meta query to the main query and have it only apply to a certain post type (i.e. event)? Pseudocode (I know this doesn't work, but to illustrate):

if ( is_search() ) {
    $query->set( 'meta_query', array(
        'relation' => 'OR',
        array(
            'key' => 'post_type',
            'value' => 'event',
            'compare' => '!=',
        ),
        array(
            ....
}

Answer 1

In the case that the start_date custom field only exists for the event post type, this works:

$query->set( 'meta_query', array(
    'relation' => 'OR',
    array(
        'key' => 'start_date',
        'compare' => 'NOT EXISTS',
    ),
    array(
        'key' => 'start_date',
        'value' => $today = date( 'Ymd' ),
        'compare' => '>=',
    ),
    array(
        'key' => 'end_date',
        'value' => $today = date( 'Ymd' ),
        'compare' => '>=',
    ),
) );

By comparing the start_date key to NOT EXISTS, the other post types are not filtered out. Obviously this is not an ideal solution, so I'm still curious if there are better ideas out there.

Answer 2

Your given answer is pretty smart!!

Another way I think you could accomplish the same thing and be a little bit more specific would be to pick a new key that exists only on the second post type and compare with EXISTS.

So your second post type is search (not exactly sure from your example). Your first post type is event. If your main query is searching through both post types, then this meta_query would include all posts of the second post type.

$query->set( 'meta_query', array(
'relation' => 'OR',
    array(
        'key' => 'my_exclusive_meta_key_for_my_other_post_type',
        'compare' => 'EXISTS',
    ),
    ...
) );