'Tests whether this resource contains a (real) field.
@param item: the field selector or Field instance'

def __contains__(self, item):

    fn = str(item)
    if ('.' in fn):
        (tn, fn) = fn.split('.', 1)
        if (tn == self.tablename):
            item = fn
    try:
        rf = self.resolve_selector(str(item))
    except (SyntaxError, AttributeError):
        return 0
    if (rf.field is not None):
        return 1
    else:
        return 0
