Question

I’m using the default JSON serialization for a model that has a number of decimal and integer attributes. An example result is:

{ "user": { "id": 1234, "rating": "98.7" } }

Notice the addition of quotes around the value of “rating”. This causes the deserialization library I’m using to incorrectly treat these as strings (instead of decimals). Can Rails be set to not use the quotes for all decimals?

Edit:

I’m on Rails 3.0.7 and Ruby 1.9.2 if that makes a difference.

Edit:

Terminal:

rails g model user rating:decimal
rake db:migrate

Console:

user = User.create(rating: 98.7)
user.to_json

Answer 1

The only “safe” way to hand decimals from language A to language B is to use a String. If your json contains "rating": 98.79999999999999 it will probably be converted to 98.79999999999998 by your JavaScript runtime.

See BigDecimal as_json documentation:

A BigDecimal would be naturally
represented as a JSON number. Most
libraries, however, parse non-integer
JSON numbers directly as floats.
Clients using those libraries would
get in general a wrong number and no
way to recover other than manually
inspecting the string with the JSON
code itself.

That’s why a JSON string is returned.
The JSON literal is not numeric, but
if the other end knows by contract
that the data is supposed to be a
BigDecimal, it still has the chance to
post-process the string and get the
real value.

If you want to force Rails not to quote these, you could monkey-patch BigDecimal (see Rails source).

# not needed: to compare with the Numeric implementation
class Numeric
  def as_json(options = nil) self end #:nodoc:
  def encode_json(encoder) to_s end #:nodoc:
end

class BigDecimal
  def as_json(options = nil) self end
  def encode_json(encoder) to_s end #:nodoc:
end