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Date: Tue, 1 Sep 2009 10:18:17 +0100
Message-ID: <46aeb24f0909010218u3c4f8d4bp45ae6a377d9f26c7@mail.gmail.com>
Subject: Re: Is fixed precision arithmetic possible in couchdb python?
From: Robert Newson <robert.newson@gmail.com>
To: user@couchdb.apache.org
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Multiply your numbers by the amount of precision you need and use
integers (*1000 for 3 d.p)? Using floating point to store money
amounts seems fraught with rounding errors.

B.

On Tue, Sep 1, 2009 at 9:58 AM, Metin Akat<akat.metin@gmail.com> wrote:
> /* Paste this in a code editor to have code highlighting */
>
> /* Here is my Map function */
> function(doc) {
> =A0if (doc.type =3D=3D "Transaction") {
> =A0 =A0for (var i =3D 0; i < doc.accounts.length; i++) {
> =A0 =A0 =A0emit(doc.accounts[i].account,
> =A0 =A0 =A0doc.accounts[i].value *
> =A0 =A0 =A0doc.accounts[i].operation
> =A0 =A0 =A0);
> =A0 =A0}
> =A0}
> }
> /* Here the value is the money transferred to or from an account and
> the operation an integer (1 or -1) showing the type (credit debit)
> of the operation */
>
> /* This is the reduce */
> function(keys, values) {
> =A0return sum(values);
> =A0}
>
>
> /* When I visit:
> http://localhost:5984/nola7accounting/_design/accounting/_view/balance?gr=
oup=3Dtrue
> I get this. The 13.05(9) is the sum of 5.03 + 8.03 (so is -13.05(9),
> only it's negative). */
> {"rows":[
> {"key":"5cf15107d977498ec4003dca0d44c579","value":-13.059999999999999},
> {"key":"b4b0c38efd4ff4c27fc63d24ae981f60","value":13.059999999999999}
> ]}
>
> /* But when I visit:
> http://localhost:5984/nola7accounting/_design/accounting/_view/balance
> In the accounting world, this should return 0 as it is the sum of all
> values (and the sum of all operations in a financial system must be
> 0),
> =A0but here is what I get: */
> {"rows":[
> {"key":null,"value":-8.881784197001252e-16}
> ]}
>
> /* OK, the above is is something close to 0, but the question is...
> how good is this for a financial software system?
> The situation is the same, no matter if I store floats or strings
> (which would represent decimals). This is probably the result
> of the weak typing in javascript (JSON).
> I wrote this view following along the "Banking" chapter of the CouchDB
> book, here:
> http://books.couchdb.org/relax/receipts/banking
> The example there is nice and working, but it works with whole numbers
> (integers).
> So, the first question is... Is there some way of working with fixed
> precision numbers in CouchdB?
> And the further question is... =A0How good is CouchDB (or any JSON
> storage) for an accounting application?
> =A0*/
>