precompile: Using Oj in Rails' ActiveSupport JSON

Recently at Everlane I ran into some interesting performance quirks with how we handled JSON serialization: wherever we called .to_json on something—even a small something—things got really slow.

We have the Oj gem in use for JSON (de)serialization, so I thought things should be fast, but after some digging it turned out that the .to_json method on objects still used the plain old JSON gem through ActiveSupport::JSON::Encoding.

Thankfully, it’s easy to switch out that encoder for a faster one:

# config/initializers/json_encoding.rb
module ActiveSupport::JSON::Encoding
  class Oj < JSONGemEncoder
    def encode value
      ::Oj.dump(value.as_json)
    end
  end
end

ActiveSupport.json_encoder = ActiveSupport::JSON::Encoding::Oj

Now go forth and have all your JSON encoding be swift!