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I am curious whether Wordpress is able to run nested meta_query, with each having different relation keys? As of Wordpress 3.0, tax_query is able to perform this function; I'm wondering whether this has an equivalent with meta_query.

$results = query_posts( array(
    'post_type' => 'event_id',
    'meta_query' => array(
        'relation' => 'AND',
            'relation' => 'OR',
                'key' => 'primary_user_id',
                'value' => $user_id
                'key' => 'secondary_user_id',
                'value' => $user_id
            'key' => 'date',
            'value' => array( $start_date, $end_date ),
            'type' => 'DATETIME',
            'compare' => 'BETWEEN'
) );


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1 Answer

That seems to be impossible. Please someone correct me if I'm wrong.

The meta_query parameter will actually be transformed into a WP_Meta_Query object, and the relation verification won't go deeper in wp-includes/meta.php, and occurs just once in the top level:

if ( isset( $meta_query['relation'] ) && strtoupper( $meta_query['relation'] ) == 'OR' ) {
    $this->relation = 'OR';
} else {
    $this->relation = 'AND';

A possible solution for this is to build your own JOIN for this query.

$query = new WP_Query( array(
    'my_meta_query' => true,
    'suppress_filters' => false
) );

add_filter( 'posts_join', 'my_meta_query_posts_join', 10, 2 );
function my_meta_query_posts_join( $join, $query ) {

    if ( empty( $query->query_vars['my_meta_query'] ) )
        return $join;

    global $wpdb;

    $new_join = "
        INNER JOIN {$wpdb->postmeta} pm1 ON 1=1
            AND pm1.post_id = {$wpdb->posts}.ID
            AND pm1.meta_key = '_some_meta_key'
            AND pm1.meta_value = 'some_value'

    return $join . ' ' . $new_join;

And if you need further verifications and rules, you can also use the posts_where filter.

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