Sum of table attributes when value is string

Question

I've never came across this before. I'm working with a table attribute whos value is a string, not float/int.

Model.first.amount => "58.00"

I need to sum up all amount. What I'm used to, with the amount being a float, would be:

Model.all.sum(&:amount) => # total value

Took a wild guess with:

Model.all.sum(&:amount.to_i) # undefined method `to_i' for :amount:Symbol

Is there a clean way to sum up the amount? Or convert the database to float?

Answer 1

Processing database with Ruby is memory inefficient.

First shot:

Model
  .pluck(:amount) # will fire sql
  .sum(&:to_f)    # convert to float, operating on resulting Array, not AR and sum

But the most effective way to process database data is SQL of course:

Model.sum("CAST(COALESCE(amount, '0') AS DECIMAL)")

1. coalesce will replace null values with '0'
2. sum all values casted to DECIMAL.