Question

So I am creating a time tracking application using Ruby On Rails and am storing the time as a number representing hours.

Since anything beyond 0.01 (36 seconds ) hours is irrelevant I only need 2 decimal places.

I am using a MySQL database with a float as the column type. While this works most of the time, every now and then i get an error with the calculation and rounding of floats.

I have done some research into my options and see that a lot of people recommend using BigDecimal. Since I use a lot of custom Database querys using calculations, so I wanted to know how changing the column type would affect this. Does it store this as a string or yaml, or is it natively supported by MySQL?

Or is there an equivalent way to do fixed-point decimal arithmetic in Ruby / Rails.

I assume any method is going to require much refactoring, how can I avoid this the most?

Any insight is appreciated.

Answer 1

MySQL does have built-in BigDecimal support. http://dev.mysql.com/doc/refman/5.1/en/precision-math-decimal-changes.html

I would suggest using that; it works well in my Rails applications. Allowing the database to handle that instead of the application makes life easier – you’re using the abstractions the way they’re designed.

Here’s the migration code:

change_column :table_name, :column_name, :decimal

Reference: Rails migration for change column