'Extend the current resource filter
@param f: a Query or a S3ResourceQuery instance
@param c: alias of the component this filter concerns,
automatically adds the respective component join
(not needed for S3ResourceQuery instances)'

def add_filter(self, f=None, c=None):

    if (f is None):
        return
    self.clear()
    if (self.rfilter is None):
        self.rfilter = S3ResourceFilter(self)
    self.rfilter.add_filter(f, component=c)
