I have a field called price in my db which is a decimal field and in my JSON API response it is returned as a String.

I wanted to apply some validations to the field that would allow max 2 digits after period and found out that if I use decimal field I can then apply the precision on DB level.

t.decimal "price", precision: 10, scale: 2

Then I want to calculate total price in a service object:

services/statistics/monthly_rides_generator.rb

class CurrentMonthRidesGenerator

    def initialize(current_user)

      @current_user = current_user

    end



    def call

      user_current_month_rides_by_day.map do |date, rides_on_day|

        {

          day: formatted_date(date),

          total_distance: total_distance(rides_on_day),

          avg_ride: avg_ride(rides_on_day),

          avg_price: avg_price(rides_on_day),

          total_price: total_price(rides_on_day)

        }

      end

    end



    ...



    def total_price(rides)

      rides.map(&:price).sum

    end

  end

app/api/statistics/stats_api.rb

get '/current_month' do

  Statistics::CurrentMonthRidesGenerator.new(current_user).call

end

but in API response this field is a String.

{

    "day": "November, 8th",

    "total_distance": "9km",

    "avg_ride": "9km",

    "avg_price": "100.0PLN",

    "total_price": "100.0"

}

I want this field to be returned as it was saved because I need a float/decimal number in the front end to then do other calculations.

Why is it returning a String when it is a decimal field? How can I fix it?

It's returning as a string because Decimal/BigDecimal in ruby is a very precise number. Javascript/JSON doesn't have a data type that is as precise as ruby's BigDecimal.

You can easily see this in your browser if you open up the console:

If you convert the value to a float in your serializer then it will be a float in the JSON object that is returned by your API, but you'll want to be careful of how your clients use this data. If they don't use a library that can handle precision then you're going to get rounding errors and often be off on your calculations by a penny.

I've been using the decimal.js library for things like this and it works out great. https://github.com/MikeMcl/decimal.js/

One way to solve this is to cast it to the desired type in a serializer:

# app/serializers/your_model_serializer.rb



class YourModelSerializer < ActiveModel::Serializer

  attributes :day,

             :total_distance,

             :avg_ride,

             :avg_price,

             :total_price



  def total_price

    object.total_price.to_f

  end

end

I decided to solve this problem by changing the column type to Float, renaming it to price_cents, adding money-rails and monetizing the column. Then I just call to_f or round the value right before displaying it or sending it to front-end in API response.