@Override
    public Set<RelationalPath<?>> visit(FactoryExpression<?> expr, Set<RelationalPath<?>> known) {
        for (Expression<?> arg : expr.getArgs()) {
            known = arg.accept(this, known);
        }
        return known;
    }
{@code RelationalPathExtractor} extracts {@link RelationalPath} instances from expressions and queries

@author tiwe
querydsl-sql/src/main/java/com/querydsl/sql/RelationalPathExtractor.java