On Aug 19, 2013, at 10:38 , Sabine Kn��fel <[hidden email]> wrote:

> Hi,
>
> I am interested in your opinion.
> I use FixedDecimal for computing currency amounts.
> This works fine.
>
> When storing the amounts with voyage into mongo (I have a lot of them!!!),
> normally, one currency amount would be stored into mongo as follows:
>
> �� �� �� �� �� "vatAmountEUR": {
> �� �� �� �� �� �� "#instanceOf": "FixedDecimal",
> �� �� �� �� �� �� "negative": false,
> �� �� �� �� �� �� "number": NumberInt(90280),
> �� �� �� �� �� �� "part1": NumberInt(9),
> �� �� �� �� �� �� "part2": NumberInt(280),
> �� �� �� �� �� �� "scale": NumberInt(4)
> �� �� �� �� ��}
>
> I think, this is a lot of stuff for one single value. I tend to convert the
> FixedDecimal into a Float for storing it. In this case, it would be like
> this:
>
> "vatAmountEUR": 0.7196
>
> When loading, I immediately re-convert it into a FixedDecimal. I would do NO
> computing with the float(!!).
>
> What is your opinion about this (rounding issues, performance, database size
> etc.)?
> Do you think, there is something against it? What would you do?
>
> Sabine

There are rounding issues even without doing arithmetic, conversion scaled -> float WILL inherently be lossy due to float's fixed size.

You are only ensured 15 decimal digits of precision with 64-bit floating point numbers like in Pharo (BSON Doubles):
98765432109.87658s5 asFloat asScaledDecimal: 5 98765432109.87659s5

Though, Compared to using NumberInt ( a signed 32-bit integer, with max 9 digits) for storing the unscaled number, it's actually the better option���

I guess the morale is, either way, as long as you are storing values in fixed size data fields (and not say, a String), you need some checks in place to ensure the numbers you are saving are within valid ranges. ;)

Cheers,
Henry

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