public static function instanceKey(array $path): string
    {
        return (new Collection($path))
            ->filter(function ($path): bool {
                // Ignore numeric path entries, as those signify an array of fields.
                // Combining the queries for those is the very purpose of the
                // batch loader, so they must not be included.
                return ! is_numeric($path);
            })
            ->implode('_');
    }