function f1_egpaf_meta_or_tax( $where, \WP_Query $q ) {
    // Get query vars.
    $tax_args = isset( $q->query_vars['tax_query'] ) ? $q->query_vars['tax_query'] : null;
    $meta_args = isset( $q->query_vars['meta_query'] ) ? $q->query_vars['meta_query'] : null;
    $meta_or_tax = isset( $q->query_vars['_meta_or_tax'] ) ? wp_validate_boolean( $q->query_vars['_meta_or_tax'] ) : false;

    // Construct the "tax OR meta" query.
    if ( $meta_or_tax && is_array( $tax_args ) && is_array( $meta_args ) ) {
        global $wpdb;
        // Primary id column.
        $field = 'ID';
        // Tax query.
        $sql_tax  = get_tax_sql( $tax_args, $wpdb->posts, $field );
        // Meta query.
        $sql_meta = get_meta_sql( $meta_args, 'post', $wpdb->posts, $field );
        // Modify the 'where' part.
        if ( isset( $sql_meta['where'] ) && isset( $sql_tax['where'] ) ) {
            $where  = str_replace(
            [ $sql_meta['where'], $sql_tax['where'] ],
            '',
            $where
            );
            $where .= sprintf(
            ' AND ( %s OR  %s ) ',
            substr( trim( $sql_meta['where'] ), 4 ),
            substr( trim( $sql_tax['where'] ), 4 )
            );
        }
    }
    return $where;
}
add_filter( 'posts_where', 'f1_egpaf_meta_or_tax', PHP_INT_MAX, 2 );

然后在WP_Query查询时,设置’_meta_or_tax’=>true。
例如:

$news_args = [
  'post_type' => ['news', 'class_news'],
  'orderby' => 'date',
  'posts_per_page' => 3,
  '_meta_or_tax'=>true,
  'tax_query' => array(
      array(
          'taxonomy' => 'class_news_category',
          'field' => 'slug',
          'terms' => $term_slugs,
          'operator'  => 'IN',
      ),
  ),
  'meta_query' => [
    [
      'key' => 'classes',
      'value' => '"' . get_the_ID() . '"',
      'compare' => 'LIKE',
    ]
  ]
];
$news_query = new WP_Query($news_args);
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