Reply To: Implement a sorting dropdown

Okay.

So say you have a single drop-down, which appends the “the_order” query variable, so the URL looks like this “…&the_order=yourvalue” on the results page. Then it is accessed on page load within the code via the $_GET['the_order'].

Here is a custom code snippet which handles that, it has examples for id, date, title, relevance and even string and numeric custom field based ordering:

// Custom ordering
add_filter(
	'asp_query_args',
	function ( $args ) {
		// The values allowed in the the_ordering variable
		$allowed_orderings = array(
			'relevance',
			'id',
			'id_reverse',
			'date',
			'date_reverse',
			'alpha',
			'alpha_reverse',
			'numeric_custom_field',
			'string_custom_field',
		);

		if ( !isset($_GET['the_order']) ) {
			return $args;
		}

		$ordering = sanitize_text_field( wp_unslash( $_GET['the_order'] ) );
		if ( !in_array($ordering, $allowed_orderings, true) ) {
			return $args;
		}

		switch ( $ordering ) {
			case 'id':
				$args['post_primary_order'] = 'id DESC';
				break;
			case 'id_reverse':
				$args['post_primary_order'] = 'id ASC';
				break;
			case 'date':
				$args['post_primary_order'] = 'post_date DESC';
				break;
			case 'date_reverse':
				$args['post_primary_order'] = 'post_date ASC';
				break;
			case 'alpha':
				$args['post_primary_order'] = 'post_title DESC';
				break;
			case 'alpha_reverse':
				$args['post_primary_order'] = 'post_title ASC';
				break;
			case 'numeric_custom_field':
				$args['post_primary_order']          = 'customfp DESC';
				$args['post_primary_order_metatype'] = 'numeric';
				$args['_post_primary_order_metakey'] = 'custom_field_name';
				break;
			case 'string_custom_field':
				$args['post_primary_order']          = 'customfp DESC';
				$args['post_primary_order_metatype'] = 'string';
				$args['_post_primary_order_metakey'] = 'custom_field_name';
				break;
			case 'relevance':
			default:
				$args['post_primary_order'] = 'relevance DESC';
				break;
		}

		return $args;
	}
);