Rails Quickstart
To universally replace Rails' use of the json gem with Oj, and also
have Oj "take over" many methods on the JSON constant (load
, parse
, etc.) with
their faster Oj counterparts, add this to an initializer:
Oj.optimize_rails()
For more details and options, read on...
Oj Rails Compatibility
The :rails
mode mimics the ActiveSupport version 5 encoder. Rails and
ActiveSupport are built around the use of the as_json(*)
method defined for
a class. Oj attempts to provide the same functionality by being a drop in
replacement with a few exceptions.
require 'oj'
Oj::Rails.set_encoder()
Oj::Rails.set_decoder()
Oj::Rails.optimize()
Oj::Rails.mimic_JSON()
or simply call
Oj.optimize_rails()
Either of those steps will setup Oj to mimic Rails but it will not change the
default mode type as the mode type is only used when calling the Oj encoding
directly. If Rails mode is also desired then use the Oj.default_options
to
change the default mode.
Some of the Oj options are supported as arguments to the encoder if called
from Oj::Rails.encode()
but when using the Oj::Rails::Encoder
class the
encode()
method does not support optional arguments as required by the
ActiveSupport compliance guidelines. The general approach Rails takes for
configuring encoding options is to either set global values or to create a new
instance of the Encoder class and provide options in the initializer.
The globals that ActiveSupport uses for encoding are:
ActiveSupport::JSON::Encoding.use_standard_json_time_format
ActiveSupport::JSON::Encoding.escape_html_entities_in_json
ActiveSupport::JSON::Encoding.time_precision
ActiveSupport::JSON::Encoding.json_encoder
Those globals are aliased to also be accessed from the ActiveSupport module
directly so ActiveSupport::JSON::Encoding.time_precision
can also be accessed
from ActiveSupport.time_precision
. Oj makes use of these globals in mimicking
Rails after the Oj::Rails.set_encode()
method is called. That also sets the
ActiveSupport.json_encoder
to the Oj::Rails::Encoder
class.
Options passed into a call to to_json()
are passed to the as_json()
methods. These are mostly ignored by Oj and simply passed on without
modifications as per the guidelines. The exception to this are the options
specific to Oj such as the :circular
option which it used to detect circular
references while encoding.
By default Oj acts like the ActiveSupport encoder and honors any changes in
the as_json()
methods. There are some optimized Oj encoders for some
classes. When the optimized encoder it toggled the as_json()
methods will not
be called for that class but instead the optimized version will be called. The
optimized version is the same as the ActiveSupport default encoding for a
given class. The optimized versions are toggled with the optimize()
and
deoptimize()
methods. There is a default optimized version for every class
that takes the visible attributes and encodes them but that may not be the
same as what Rails uses. Trial and error is the best approach for classes not
listed here.
The classes that can be put in optimized mode and are optimized when
Oj::Rails.optimize
is called with no arguments are:
- Array
- BigDecimal
- Float
- Hash
- Range
- Regexp
- Time
- ActiveSupport::TimeWithZone
- ActionController::Parameters
- any class inheriting from ActiveRecord::Base
- any other class where all attributes should be dumped
The ActiveSupport decoder is the JSON.parse()
method. Calling the
Oj::Rails.set_decoder()
method replaces that method with the Oj equivalent.
Usage in Rails 3
To support Rails 3 you can create a new module mixin to prepend to controllers:
require 'oj'
module OjJsonEncoder
def render( = nil, = {}, &block)
if && .is_a?(Hash) && [:json]
obj = .delete(:json)
obj = Oj.dump(obj, :mode => :rails) unless obj.is_a?(String)
[:text] = obj
response.content_type ||= Mime::JSON
end
super
end
end
Usage:
class MyController < ApplicationController
prepend OjJsonEncoder
def index
render :json => { :hello => 'world' }
end
end
Older Ruby Version Support (Pre 2.3.0)
If you are using an older version of Ruby, you can pin oj
to an earlier version in your Gemfile:
gem 'oj', '3.7.12'
Notes:
Optimized Floats set the significant digits to 16. This is different than Ruby which is used by the json gem and by Rails. Ruby varies the significant digits which can be either 16 or 17 depending on the value.
Optimized Hashes do not collapse keys that become the same in the output. As an example, a non-String object that has a
to_s()
method will become the return value of theto_s()
method in the output without checking to see if that has already been used. This could occur is a mix of String and Symbols are used as keys or if a other non-String objects such as Numerics are mixed with numbers as Strings.To verify Oj is being used turn on the Oj
:trace
option. Similar to the Ruby Tracer Oj will then print out trace information. Another approach is to turn on C extension tracing. Settracer = TracePoint.new(:c_call) do |tp| p [tp.lineno, tp.event, tp.defined_class, tp.method_id] end
or, in older Rubies, setTracer.display_c_call = true
.
For example:
```
require 'active_support/core_ext'
require 'active_support/json'
require 'oj'
Oj.optimize_rails
tracer.enable { Time.now.to_json }
# prints output including
....
[20, :c_call, #<Class:Oj::Rails::Encoder>, :new]
[20, :c_call, Oj::Rails::Encoder, :encode]
....
=> "\"2018-02-23T12:13:42.493-06:00\""
```