i've got a price field/column and i wonder should the rails datatype be string, decimal or float?
eg. 15.50 USD.
thanks
+1
A:
It depends.
If you are performing calculations for purchase prices use a decimal.
If you are performing engineering mathematics use a float.
If you are just storing the data use a string.
Woot4Moo
2010-06-17 17:26:35
+2
A:
add_column :table, :price, :decimal, :precision => 8, :scale => 2
The code above would be your best bet.
Tom
2010-06-17 17:38:33
how do i do it in the command line? i typed "rails generate scaffold Product price:decimal" and it created a column with :scale 1.
never_had_a_name
2010-06-17 17:43:33
Depending on your needs, you might want to add -> add_column :table, :currency, :string, :default => 'USD'
Tom
2010-06-17 17:43:49
Is this Rails 3? rails g migration AddPriceToYourModel price:decimal then go to the generated migration and add in the details.
Tom
2010-06-17 17:45:33
@Tom. where do you find all the options like precision and scale? im on ror3 but cant find the options in the migrations page.
never_had_a_name
2010-06-17 18:42:49
If you run rails g migration AddPriceToYourModel price:decimal and go to [some timestamp]_add_price_to_yourmodel you should see add_column :table, :price, :decimal. Just append ', :precision => 8, :scale => 2' to that line.
Tom
2010-06-17 19:03:02
A:
I recommend using integers for prices if possible. Many popular gems (such as ActiveMerchant, Money) assume the use of integers, and it is often better to store units of measurement in a base unit (such as cents).
Kevin Sylvestre
2010-06-17 18:25:14
That is why you base it on cents. So the $13.25 gets stored as 1325 in the database. You format the dollar sign and the decimal in the view.
sosborn
2010-06-17 23:32:25
+1
A:
Floats are not accurate:
0.3 - 0.2 - 0.1
=> -2.77555756156289e-17
Don't use them unless you only store values.
If you need to make calculations store the price in cents as an integer. You can easily display them as USD with a helper.
vise
2010-06-17 20:12:32
+1
A:
This argument always has two sides - decimals and integers. Supporters of integers argue that decimals might not be accurate (when doing conversions) and that the BigDecimal implementation includes bugs, sometimes even segfaulting.
For my own project, i picked up integers also, wrapped them in a custom container, converting cents to "real" amounts and back. At first it seemed nice, after a while it became really cumbersome to use - tracking when you are dealing with cents, when with formatted strings etc.
Then i reverted to decimals - same format all the time, i can easily convert the amount to cents if needed, i get the different rounding algorithms out of the box. Im much much more satisfied with decimals.
And to address the issues about decimals not being accurate - when googling you might notice that most of the bugs are related to converting decimals into floats :) As vise already mentioned before, floats are not accurate and you should never ever convert your decimal to a float. That's the single most important thing you have to remember when dealing with decimals - you don't want to lose accuracy by conversions. Oh and i have never actually encountered any bugs with ruby 1.8.7, 1.8.7 and 1.9.1 while using BigDecimal extensively.
Tanel Suurhans
2010-06-18 18:31:02