vr.order = order; vr.filter = filter; vr.maxSize = maxSize; vr.constraints = constraints;
    Relation getVirtualPropertyRelation() {        if (!virtual) {            throw new RuntimeException("getVirtualPropertyRelation called on non-virtual relation");        }        Relation vr = new Relation(this);        vr.groupby = groupby;        vr.groupbyOrder = groupbyOrder;        vr.groupbyPrototype = groupbyPrototype;        vr.order = order;        vr.filter = filter;        vr.maxSize = maxSize;        vr.constraints = constraints;        return vr;    }