Float with many digits automatically becomes BigDecimal when using Oj

[kyoshidajp]

Detail

If a document has coordinates field with [131.01468600332737, 43.0554632], then call Elastic::Transport::Client#perform_request like the following PoC.

# poc.rb

require 'elastic/transport'
require 'oj'

client = Elastic::Transport::Client.new(hosts: { host: "localhost", port: 9200})
body = {
  from: 0,
  size: 1,
  query: {
    match: {
      key: "5yc1x"
    }
  }
}

response = client.perform_request('GET', 'development/_search', {}, body)

coordinates = response.body['hits']['hits'][0]['_source']['coordinates']
p coordinates
p coordinates.map(&:class)

% bundle exec ruby poc.rb
[0.13101468600332737e3, 43.0554632]
[BigDecimal, Float]

But if remove require 'oj', then

% bundle exec ruby poc.rb
[131.01468600332737, 43.0554632]
[Float, Float]

This difference depends on the mode of oj used by MultiJson. MultiJson loads JSON with oj as strict mode by default.

> num_str = "1.11111111111111111"

> MultiJson.load(num_str).class
BigDecimal < Numeric

> Oj.load(num_str, {mode: :strict}).class
BigDecimal < Numeric

> Oj.load(num_str, {mode: :null}).class
BigDecimal < Numeric

> Oj.load(num_str, {mode: :compat}).class
Float < Numeric

> Oj.load(num_str, {mode: :rails}).class
BigDecimal < Numeric

> Oj.load(num_str, {mode: :object}).class
BigDecimal < Numeric

> Oj.load(num_str, {mode: :custom}).class
BigDecimal < Numeric

MultiJson allows other JSON engines to be selected, while all others remain Float.

What kind do we have trouble?

For example, when returning JSON value in an API endpoint, it is not possible to specify either a numeric or a string as the value type. Therefore, unintended type conversion is required only when using oj.

> Oj.load(num_str, {mode: :strict}).as_json
"1.11111111111111111"
> Oj.load(num_str, {mode: :strict}).as_json.class
String < Object

> Oj.load(num_str, {mode: :compat}).as_json
1.1111111111111112
> Oj.load(num_str, {mode: :compat}).as_json.class
Float < Numeric