Add to ElasticPress the capability to partially match a WooCommerce SKU.

elasticpress-partial-matches-on-woocommerce-skus.php

<?php
/**
 * Add the ngram analyzer if not added yet by autosuggest.
 *
 * @param array $mapping The mapping array.
 * @return array
 */
function ep_custom_add_edge_ngram_analyzer( $mapping ) {
	if ( ! @isset( $mapping['settings']['analysis']['analyzer']['edge_ngram_analyzer'] ) ) {
		$mapping['settings']['analysis']['analyzer']['edge_ngram_analyzer'] = array(
			'type'      => 'custom',
			'tokenizer' => 'standard',
			'filter'    => array(
				'lowercase',
				'edge_ngram',
			),
		);
	}

	return $mapping;
}
add_filter( 'ep_post_mapping', 'ep_custom_add_edge_ngram_analyzer', 11 );

/**
 * Add custom SKU field mapping
 *
 * @param array $mapping The mapping array.
 * @return array
 */
function ep_custom_add_sku_field( $mapping ) {
	if ( version_compare( \ElasticPress\Elasticsearch::factory()->get_elasticsearch_version(), '7.0', '<' ) ) {
		$post_mapping = &$mapping['mappings']['post'];
	} else {
		$post_mapping = &$mapping['mappings'];
	}

	$post_mapping['properties']['product_sku'] = [
		'type'   => 'text',
		'fields' => [
			'raw'     => [
				'type'         => 'keyword',
				'ignore_above' => 10922,
			],
			'suggest' => [
				'type'            => 'text',
				'analyzer'        => 'edge_ngram_analyzer',
				'search_analyzer' => 'standard',
			],
		],
	];

	return $mapping;
}
add_filter( 'ep_post_mapping', 'ep_custom_add_sku_field', 11 );

/**
 * Add the SKU value to the custom SKU field in the Elasticsearch document.
 *
 * @param array $post_args Post data.
 * @param int   $post_id   Post ID.
 * @return array
 */
function ep_custom_set_product_sku( $post_args, $post_id ) {
	if ( 'product' !== $post_args['post_type'] ) {
		return $post_args;
	}

	$sku = get_post_meta( $post_id, '_sku', true );
	if ( ! empty( $sku ) ) {
		$post_args['product_sku'] = $sku;
	}

	return $post_args;
}
add_filter( 'ep_post_sync_args_post_prepare_meta', 'ep_custom_set_product_sku', 10, 2 );

/**
 * If weighting is in use, apply to the custom field the same behavior set for regular SKU.
 *
 * @param array $weight_config Weighting config.
 * @return array
 */
function ep_custom_search_custom_sku_field( $weight_config ) {
	if ( ! empty( $weight_config['product'] ) ) {
		$weight_config['product']['product_sku.suggest'] = $weight_config['product']['meta._sku.value'];
	}
	return $weight_config;
}
add_filter( 'ep_weighting_configuration_for_search', 'ep_custom_search_custom_sku_field' );

/**
 * If weighting is not use, adjust default values to use custom SKU.
 *
 * @param array  $defaults  Default values per post type.
 * @param string $post_type Post type slug.
 * @return array
 */
function ep_custom_search_custom_sku_field_by_default( $defaults, $post_type ) {
	if ( 'product' !== $post_type ) {
		return $defaults;
	}

	$defaults['product_sku.suggest'] = array(
		'enabled' => true,
		'weight'  => 1,
	);

	return $defaults;
}
add_filter( 'ep_weighting_default_post_type_weights', 'ep_custom_search_custom_sku_field_by_default', 10, 2 );