ElasticPress - Index product variation titles into the parent product

ep-product-variation-titles.php

<?php

// Create a new field with product variation titles.
add_filter(
	'ep_prepare_meta_data',
	function( $post_meta, $post ) {
		if ( 'product' !== get_post_type( $post ) ) {
			return $post_meta;
		}
​
		$product            = wc_get_product( $post );
		$product_variations = $product->get_children();
​
		if ( $product_variations ) {
			$variation_titles = [];
			foreach ( $product_variations as $product_var_id ) {
				$variation_titles[] = get_the_title( $product_var_id );
			}
​
			$post_meta['product_variation_titles'] = wp_json_encode( $variation_titles );
		}
​
		return $post_meta;
	},
	10,
	2
);
​
// Add the new field to the weighting dashboard.
add_filter(
	'ep_weighting_fields_for_post_type',
	function( $fields, $post_type ) {
		if ( 'product' === $post_type ) {
			if ( empty( $fields['meta'] ) ) {
				$fields['meta'] = array(
					'label'    => 'Custom Fields',
					'children' => array(),
				);
			}
​
			$key = 'meta.product_variation_titles.value';
​
			$fields['meta']['children'][ $key ] = array(
				'key'   => $key,
				'label' => 'Product Variation Titles',
			);
		}
​
		return $fields;
	},
	10,
	2
);