I think that Puneet is suggesting to have a syntax for non-mandatory parts in the route specifier, i.e. the foo_id might be there, as in:
/foo/1/bar/30
or not, as in
/foo/bar/30
in which case a default value for foo_id can be set inside the route handler. Trying to guess a possible regex for it (don't know if "\w" is correct here):
/foo(?:/(?<foo_id>:\w+))?/bar(?:/(?<bar_id>:\w+))
i.e. each named capture "name" for a parameter is expanded to "(?:/(?<name>:\w+))?" (or whatever is used instead of "\w" today).
Cheers,
Flavio.