functions.php

<?php


if ( defined( 'YITH_WCAS_PREMIUM' ) ) {

	add_action( 'ywcas_before_do_the_request', 'yith_wcas_query_fix' );
	function yith_wcas_query_fix() {
		global $yith_wcas, $wp_the_query;
		remove_filter( 'posts_where', array( $yith_wcas, 'extend_search_where' ) );
		remove_filter( 'posts_join', array( $yith_wcas, 'extend_search_join' ) );


		if ( isset($_REQUEST['action']) && 'yith_ajax_search_products' == $_REQUEST['action'] ) {
			add_filter( 'posts_where',  'ywcas_extend_search_where' );
			add_filter( 'posts_join',  'ywcas_extend_search_join'  );
		}

	}

	add_action( 'pre_get_posts',  'ywcas_pre_get_posts' , 15 );
	function ywcas_pre_get_posts() {
		global $yith_wcas, $wp_the_query;

		remove_filter( 'posts_join', array( $yith_wcas, 'search_post_join' ) );
		remove_filter( 'posts_where', array( $yith_wcas, 'search_post_where' ) );

		if ( ! is_admin() && ! empty( $wp_the_query->query_vars['s'] ) && ! ( defined( 'DOING_AJAX' ) && DOING_AJAX ) ) {
			add_filter( 'posts_where',  'ywcas_extend_search_where' );
			add_filter( 'posts_join',  'ywcas_extend_search_join'  );
		}

	}

	function ywcas_extend_search_join( $join ) {
		global $yith_wcas;
		global $wpdb;

		$search_string = $yith_wcas->get_search_string();
		if( $search_string == ''){
			return $join;
		}
		$join = '';
		// YITH WooCommerce Brands Compatibility.
		$search_by_brand = isset( $yith_wcas->search_options['search_by_brand'] ) && 'yes' === $yith_wcas->search_options['search_by_brand'];

		if ( 'yes' === $yith_wcas->search_options['search_by_cat'] || 'yes' === $yith_wcas->search_options['search_by_tag'] || $search_by_brand || apply_filters( 'yith_wcas_search_for_taxonomy', false ) ) {
			$join .= " LEFT JOIN {$wpdb->term_relationships} tr ON {$wpdb->posts}.ID = tr.object_id LEFT JOIN {$wpdb->term_taxonomy} tt ON tt.term_taxonomy_id=tr.term_taxonomy_id LEFT JOIN {$wpdb->terms} tm ON tm.term_id = tt.term_id";
		}

		$product_visibility_term_ids = wc_get_product_visibility_term_ids();
		$join                        .= " LEFT JOIN {$wpdb->term_relationships} tr_v ON {$wpdb->posts}.ID = tr_v.object_id LEFT JOIN {$wpdb->term_taxonomy} tt_v ON ( tt_v.term_taxonomy_id=tr_v.term_taxonomy_id AND tt_v.taxonomy LIKE 'product_visibility' AND tt_v.term_taxonomy_id NOT IN ( " . $product_visibility_term_ids['exclude-from-search'] . " ) ) LEFT JOIN {$wpdb->terms} tm_v ON tm_v.term_id = tt_v.term_id";

		if ( '_sku' === $yith_wcas->search_options['search_by_cf'] ) {
			$join .= " LEFT JOIN {$wpdb->wc_product_meta_lookup} as cf1 ON {$wpdb->posts}.ID = cf1.product_id ";
		}

		return $join;
	}


	function ywcas_extend_search_where( $where ) {
		global $yith_wcas, $wpdb;
		$search_string = $yith_wcas->get_search_string();
		if( $search_string == ''){
			return $where;
		}
		$terms         = array();
		$where         =  '';



		// YITH WooCommerce Brands Compatibility.
		if ( class_exists( 'YITH_WCBR' ) ) {
			if ( isset( $yith_wcas->search_options['search_by_brand'] ) && 'yes' === $yith_wcas->search_options['search_by_brand']  ) {
				if ( ! in_array( YITH_WCBR::$brands_taxonomy, $terms ) ) {
					$terms[] = YITH_WCBR::$brands_taxonomy;
				}
			}
		}



		// YITH WooCommerce Brands Compatibility.
		$terms = apply_filters( 'yith_wcas_search_taxonomy_terms', $terms );

		$reverse = false;

		$where .= " AND {$wpdb->posts}.post_type LIKE 'product' AND (";

		if ( $yith_wcas->search_options['like'] ) {

			$where .= $reverse ? '(' : '';

			if ( 'yes' === $yith_wcas->search_options['search_by_title'] ) {
				$where .= "  ( LOWER( {$wpdb->posts}.post_title ) LIKE '" . $search_string . "') ";
				$where .= $reverse ? " OR ( LOWER( {$wpdb->posts}.post_title ) LIKE '" . $search_string . "') )" : '';
			} else {
				$where .= " 1=2 ";
			}


			if ( '_sku' === $yith_wcas->search_options['search_by_cf'] ) {
				$where .= " OR ( LOWER(cf1.sku) LIKE '{$search_string}' )  ";
			}

			$addor = true;

			if ( ! empty( $terms ) ) {
				$where .= ( $addor ) ? ' OR ' : '';
				$where .= " (( LOWER(tm.name) LIKE '" . $search_string . "' OR LOWER(tm.slug) LIKE '" . $search_string . "') AND tt.taxonomy IN ('" . implode( "','", $terms ) . "')) ";
			}

			$where .= ' ) ';

		} else {

			$where .= $reverse ? '(' : '';
			if ( 'yes' === $yith_wcas->search_options['search_by_title'] ) {
				$where .= "  ( LOWER( {$wpdb->posts}.post_title ) REGEXP  '" . $search_string . "') ";
				$where .= $reverse ? " OR ( LOWER( {$wpdb->posts}.post_title ) REGEXP '" . $yith_wcas->search_reverse_string . "') )" : '';
			} else {
				$where .= " 1=2 ";
			}


			if ( '_sku' === $yith_wcas->search_options['search_by_cf'] ) {
				$where .= " OR ( LOWER(cf1.sku) REGEXP '{$search_string}' )  ";
			}

			$addor = true;

			if ( ! empty( $terms ) ) {
				$where .= ( $addor ) ? ' OR ' : '';
				$where .= " (( LOWER(tm.name) REGEXP '" . $search_string . "' OR LOWER(tm.slug) REGEXP '" . $search_string . "') AND tt.taxonomy IN ('" . implode( "','", $terms ) . "')) ";
			}

			$where .= ' ) ';

			if ( 'yes' === $yith_wcas->search_options['search_by_author'] ) {
				$where .= " OR us.user_nicename REGEXP '" . $search_string . "' ";
			}
		}

		$where = apply_filters( 'yith_wcas_search_where', $where, $search_string );

		return $where;
	}
}