对SQLAlchemy中的多个列进行排序的语法

Question

I am currently using SQLAlchemy to query my database as such:

returnedOrders = session.query(ORDER).join(RESTAURANT, 
                 and_(ORDER.RESTAURANTSID==RESTAURANT.RESTAURANTSID))\
                 .filter(ORDER.RESTAURANTSID==restaurantID)\
                 .order_by(sortOrders(sort_method))\
                 .all()

def sortOrders(sort_method):
    # Date in ascending order
    if sort_method == 'date':
        return ORDER.ORDERSDATE
    # Date in descending order
    elif sort_method == '-date':
        return desc(ORDER.ORDERSDATE)          
    # Restaurant then Cost in ascending order
    elif sort_method == 'restaurant,cost':
        return RESTAURANT.RESTAURANTSNAME, ORDER.ORDERSCOST(???? Error -
                                           SQL expression object or string expected.)
    # Restaurant in ascending order then Cost in descending order
    elif sort_method == 'restaurant,-cost':
        return ???

This seems to be working for the queries that only involve one column . I'm now trying to figure out how to do this for the last two if statements but can't seem to get the syntax right.

Is this even possible?

Any help with this would be greatly appreciated.

Answer 1

It currently does not work because order_by does not work with tuple instances. To fix this, you need to expand the arguments to the order_by(...) . One way to do it would be to always expand (using * [star]) and always return tuples:

returnedOrders = (session
                  .query(ORDER)
                  .join(RESTAURANT, and_(ORDER.RESTAURANTSID==RESTAURANT.RESTAURANTSID))
                  .filter(ORDER.RESTAURANTSID==restaurantID)
                  .order_by(*sortOrders(sort_method))  # expand tuples
                  .all()
                  )

def sortOrders(sort_method):
    if sort_method == 'date':
        return (ORDER.ORDERSDATE,)  # @new: return tuple
    elif sort_method == '-date':
        return (ORDER.ORDERSDATE.desc(),)  # @new: return tuple
    elif sort_method == 'restaurant,cost':
        return (
            RESTAURANT.RESTAURANTSNAME,
            ORDER.ORDERSCOST,
        )
    elif sort_method == 'restaurant,-cost':
        return (
            RESTAURANT.RESTAURANTSNAME,
            ORDER.ORDERSCOST.desc(),
        )
    else:
        assert False, "Unexpected sort method {}".format(sort_method)