# Financial app - decimal to float conversion problem **URL:** \ **Category:** Rails\ **Created:** [February 15, 2006, 7:56pm UTC](https://www.ruby-forum.com/t/financial-app-decimal-to-float-conversion-problem/68750 "2006-02-15T19:56:18Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![srjweb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/8e8cbc/32.png) [@srjweb](https://www.ruby-forum.com/u/srjweb)\ **Post date:** [February 15, 2006, 7:56pm UTC](https://www.ruby-forum.com/t/financial-app-decimal-to-float-conversion-problem/68750/1 "2006-02-15T19:56:18Z")
I’m having problems with using Rails for a financial application: the database stores financial fields as decimal, but ActiveRecord converts these to float - so I get the rounding errors you’d expect ([Floating Point : Java Glossary](http://www.mindprod.com/jgloss/floatingpoint.html)). This has come up recently, and the recommended fix seems to be to be Tobi Luetke’s ‘money’ gem ([http://article.gmane.org/gmane.comp.lang.ruby.rails/46632/match=money+bigdecimal](http://article.gmane.org/gmane.comp.lang.ruby.rails/46632/match=money+bigdecimal)) but this won’t work for me: I’ve inherited the (SQLServer) database, and financial fields are defined as decimal: I can’t insist on changing everything to integer values in cents. What seems to be needed is changing the Ruby type mapping, which seems to be a ‘good idea’ that’s come up before ([http://article.gmane.org/gmane.comp.lang.ruby.rails/713](http://article.gmane.org/gmane.comp.lang.ruby.rails/713)) but hasn’t made it into Rails, at least not 1.0. Have people tried and given up? What would be involved? I’ve had a poke around abstract\_adapter.rb and sqlserver\_adapter.rb and can see some places to hack, but haven’t followed through the implications. I don’t mind adding a dependency on bigdecimal, even if only the resulting fix could only be distributed as a plugin rather than a patch to the Rails trunk. Any help, hacks or workarounds much appreciated - if I can’t solve this problem in Rails, my chances of selling Ruby and Rails internally more or less vanish… thanks Stuart ---
**Author:** ![srjweb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/8e8cbc/32.png) [@srjweb](https://www.ruby-forum.com/u/srjweb)\ **Post date:** [February 15, 2006, 11:21pm UTC](https://www.ruby-forum.com/t/financial-app-decimal-to-float-conversion-problem/68750/2 "2006-02-15T23:21:03Z")
On 15/02/06, Stuart J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Any help, hacks or workarounds much appreciated - if I can’t solve this > problem in Rails, my chances of selling Ruby and Rails internally more > or less vanish… ## To avoid floating point conversion, I multiply currency values before calculation by 100 (for 2 decimal places), perform my operation, and finally divide by 100. Perhaps this will work for you as well? Cheers, Hasan D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![srjweb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/8e8cbc/32.png) [@srjweb](https://www.ruby-forum.com/u/srjweb)\ **Post date:** [May 3, 2006, 6:58pm UTC](https://www.ruby-forum.com/t/financial-app-decimal-to-float-conversion-problem/68750/3 "2006-05-03T18:58:11Z")
A new ruby library is being developed on [rubyforge.org](http://rubyforge.org), which can handle numbers of the type stored in databases, with a fixed number of digits after the decimal point. It is called long-decimal, can be installed with gem install long-decimal and should be stable if you want to use +, -, \*, sqrt and /. Beyond the functionality of similar classes of Java it can also do some transcendental functions like exp and log, which are not quite as stable now, so that the whole library is still called alpha. Maybe it would be a good idea to use exactly this type for active records when mapping decimals of databases to ruby. Best regards, Karl