Summing column_property values

Question

I have two column_property columns that I'd like to sum together in the grandtotal column. I want to be able to sort and filter against the grandtotal column.

How can I sum the subtotal and shipping columns' values?

Code:

subtotal = orm.column_property(
    select([case(
        [(func.sum(OrderProductModel.subtotal).is_(None), 0)],
        else_=func.sum(OrderProductModel.subtotal))
    ]).where(OrderProductModel.order_id == id))
shipping = orm.column_property(case(
    [(is_expedited.is_(True), shipping_rate)], else_=Decimal(0.00)))
grandtotal = orm.column_property(func.sum(subtotal + shipping))

Error:

TypeError: unsupported operand type(s) for +: 'ColumnProperty' and 'ColumnProperty'

Answer 1

You need to summing expressions of this column properties

grandtotal = orm.column_property(func.sum(subtotal.expression + shipping.expression))