nal child indexables for a given term.
	 */
	public function get_children_for_term( $term_id, array $child_indexables ) {
		// Finds object_ids (posts) for the term.
		$post_object_ids = $this->get_object_ids_for_term( $term_id, $child_indexables );

		// Removes the objects that are already present in the children.
		$existing_post_indexables = \array_filter(
			$child_indexables,
			function( $indexable ) {
				return $indexable->object_type === 'post';
			}
		);

		$existing_post_object_ids = \wp_list_pluck( $existing_post_indexables, 'object_id' );
		$post_object_ids          = \array_diff( $post_object_ids, $existing_post_object_ids );

		// Finds the indexables for the fetched post_object_ids.
		$post_indexables = $this->indexable_repository->find_by_multiple_ids_and_type( $post_object_ids, 'post', false );

		// Finds the indexables for the posts that are attached to the term.
		$post_indexable_ids       = \wp_list_pluck( $post_indexables, 'id' );
		$additional_indexable_ids = $this->indexable_hierarchy_repository->find_children_by_ancestor_ids( $post_indexable_ids );

		// Makes sure we only have indexable id's that we haven't fetched before.
		$additional_indexable_ids = \array_diff( $additional_indexable_ids, $post_indexable_ids );

		// Finds the additional indexables.
		$additional_indexables = $this->indexable_repository->find_by_ids( $additional_indexable_ids );

		// Merges all fetched indexables.
		return \array_merge( $post_indexables, $additional_indexables );
	}

	/**
	 * Updates the indexable hierarchy and indexable permalink.
	 *
	 * @param Indexable $indexable The indexable to update the hierarchy and permalink for.
	 */
	protected function update_hierarchy_and_permalink( $indexable ) {
		$this->indexable_hierarchy_builder->build( $indexable );

		$indexable->permalink = $this->permalink_helper->get_permalink_for_indexable( $indexable );
		$indexable->save();
	}

	/**
	 * Retrieves the object id's for a term based on the term-post relationship.
	 *
	 * @param int         $term_id          The term to get the object id's for.
	 * @param Indexable[] $child_indexables The child indexables.
	 *
	 * @return array List with object ids for the term.
	 */
	protected function get_object_ids_for_term( $term_id, $child_indexables ) {
		$filter_terms = function( $child ) {
			return $child->object_type === 'term';
		};

		$child_terms      = \array_filter( $child_indexables, $filter_terms );
		$child_object_ids = \wp_list_pluck( $child_terms, 'object_id' );

		// Get the term-taxonomy id's for the term and its children.
		$term_taxonomy_ids = $this->wpdb->get_col(
			$this->wpdb->prepare(
				'SELECT term_taxonomy_id
				FROM ' . $this->wpdb->term_taxonomy . '
				WHERE term_id IN( ' . \implode( ', ', \array_fill( 0, ( \count( $child_object_ids ) + 1 ), '%s' ) ) . ' )',
				$term_id,
				...$child_object_ids
			)
		);

		// In the case of faulty data having been saved the above query can return 0 results.
		if ( empty( $term_taxonomy_ids ) ) {
			return [];
		}

		// Get the (post) object id's that are attached to the term.
		return $this->wpdb->get_col(
			$this->wpdb->prepare(
				'SELECT DISTINCT object_id
				FROM ' . $this->wpdb->term_relationships . '
				WHERE term_taxonomy_id IN( ' . \implode( ', ', \array_fill( 0, \count( $term_taxonomy_ids ), '%s' ) ) . ' )',
				...$term_taxonomy_ids
			)
		);
	}
}