Hi,
Some time ago I asked if there is a way to aggregate on an expression
and I was told that it's not possible at the moment. I managed to use
a mix of aggregation and some arithmetics to reduce processing time by
a factor of 20 in critical areas of my application. While doing so, I
felt that some kind of a new field-type could be useful and perhaps
lead to make aggregation on expressions possible. Something like an
ExpressionField (or SQLField or whatever ...) that does some SQL
processing directly on the database and that could be used like this:
class InvoiceLine():
price = DecimalField()
quantity = DecimalField()
total = ExpressionField('price*quantity')
invoice = ForeignKey(Invoice)
One could do:
invoice.invoiceline_set.objects.aggregate(Sum('total'))
Is this a reasonable approach and is it perhaps already in the
timeline?
Marc
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