How to modify JSON returned from Rails controller

Question

The standard mechanism I return JSON in a Rails controller is with:

respond_to do |format|
  format.html
  format.json { render json: @cars }
end

Is there a way to modify the @cars JSON? In particular I simply want to add 4 extra fields in there.

UPDATE: Sorry, I should've explained a little more. @cars contains a list of Car objects. I want to add 4 fields to each Car object in the JSON. This is unique to a particular controller, so I don't want to make an as_json method as that would affect other JSONs of this class.

is @cars a result set from the Car Model? also are these 4 fields unique to each record, or a superset and adjacent to a collection of cars? — blotto
– blotto, Commented Feb 12, 2014 at 0:46
You mean, you want to add 4 extra fields outside of the car object? like: {total_records: 4, current_page: 1, per_page: 2, cars: [{...},{...}]} — Muntasim
– Muntasim, Commented Feb 12, 2014 at 1:07
@at.: As I wrote in another comment, you can easily use to_json(:exclude => [], :methods => []). See my answer for more details on it — Francesco Belladonna
– Francesco Belladonna, Commented Feb 12, 2014 at 3:27
@at. You can pass all of the options that you would normally pass to the #as_json method to #to_json in your controller. OR, you could create a custom ActiveModelSerializer and only use it once in the controller: render json: @cars, serializer: MyCustomCarSerializer — deadwards
– deadwards, Commented Feb 13, 2014 at 20:17

nakwa · Accepted Answer · 2014-02-12 11:39:27Z

3

You can also add custom or nested fields with something like:

class MyModel < ActiveRecord::Base

  def as_json(options)
    super(options).merge({
      "custom" => "myvalue",
      :name => self.name.titleize,
      "result" => self.my_method(self.value1)
    })
  end
end

answered Feb 12, 2014 at 11:39

nakwa

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Comments

Francesco Belladonna · Accepted Answer · 2014-02-12 03:51:11Z

2

If you have to do it once, you should use to_json ( http://apidock.com/rails/ActiveRecord/Serialization/to_json ) in this way, directly in your controller:

@object.to_json(:except => ['created_at', 'updated_at'], :methods => ['method1', 'method2'])

In :methods you can specify additional methods you want include.

activemodel_serializer should be used only if you do it very often (for example on a JSON API), if you do it only once in your project, you shouldn't do it.

You can also use the default Rails 4 builder if you are actually using Rails 4.
Notice that the most famous gem for building JSON is RABL, but I do prefer activemodel_serializer. There is also a very nice railscasts available for free about it.

edited Feb 12, 2014 at 3:51

answered Feb 12, 2014 at 3:14

Francesco Belladonna

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4 Comments

at. Over a year ago

Love the to_json method, but how do I use it with render json: @cars? Instead of @cars I can pass @cars.to_json(...)?

Francesco Belladonna Over a year ago

I don't know about this, I mean, I did it but I don't know the "official" way, I suppose you can just render @obj.to_json(blabla) and nothing else, otherwise use one like :inline or :text, or even better, I suggest you to make a different question for this. Anyway, here is the doc: guides.rubyonrails.org/layouts_and_rendering.html#using-render

Francesco Belladonna Over a year ago

You can check this post: jonathanjulian.com/2010/04/rails-to_json-or-as_json there are some suggestions about it. Even better, check this stackoverflow question that explains this clearly: stackoverflow.com/questions/2572284/…

at. Over a year ago

Looks like this is correct, though as_json seems more appropriate instead of to_json. as_json just creates the data structure, to_json also renders it.

deadwards · Accepted Answer · 2014-02-12 01:05:41Z

2

There are two ways that you can modify the structure of the json returned.

Override the #as_json method on the model

model Car < ActiveRecord::Base

  def as_json(options={})
    opts = {
      :only => [:id, :name],
      :methods => [:custom_method]
    }

    super(options.merge(opts))
  end

  def custom_method
    # some extra info (possibly calculated values)
  end

end

You can use the active_model_serializer gem. This is my preferred method because it comes with a few built-in conveniences.

class CarSerializer < ActiveModel::Serializer
  attributes :id, :name, :custom_method

  def custom_method
    # method only available within serializer
  end
end

answered Feb 12, 2014 at 1:05

deadwards

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Comments

lalameat · Accepted Answer · 2014-02-12 03:16:47Z

0

I think it could use a method to do the adding fields process and render the return result. Could the following work for you:

In a helper

def some_method(in_param, from_which_controller)
  return_array = Array.new
  obj_array = JSON.parse(in_param);
  obj_array.each do |obj|
    case from_which_controller
      when from_controller_a
         # add the field to obj or some other thing
      when ...........
         # add the field to obj or some other thing
    end
    return_array << obj # or new obj instead of obj
  end
  return return_array.to_json
end

In your controller:

respond_to do |format|
  format.html
  format.json { render json: some_method(@cars, this_controller) }
end

answered Feb 12, 2014 at 3:16

lalameat

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Comments

Muntasim · Accepted Answer · 2014-02-12 04:39:31Z

0

If you want to edit the json then you can use ActiveSupport::JSON.decode to decode the json. It will give you an array of hash which is easily modifiable and then you can convert that to json using to_sosn

Example: I have used rails console to demonstrate. You need the last portion only.

>> cars = [{id: 1,name: 'foo'}, {id:2, name: 'bar'}]
[{:id=>1, :name=>"foo"}, {:id=>2, :name=>"bar"}]

>> json = cars.to_json
"[{\"id\":1,\"name\":\"foo\"},{\"id\":2,\"name\":\"bar\"}]"

>> parsed_json = ActiveSupport::JSON.decode json
[{"id"=>1, "name"=>"foo"}, {"id"=>2, "name"=>"bar"}]

Then you can iterate that array and modify where necessary and convert back to json

edited Feb 12, 2014 at 4:39

answered Feb 12, 2014 at 2:44

Muntasim

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4 Comments

Francesco Belladonna Over a year ago

Sorry I don't like to downvote but I find crazy get a memory object, convert it to a string, reconverting it to a memory object (when you already have it) and then send it out as a json, you triple memory usage, waste cpu cycles for something that can be done much better like the as_json method or github.com/rails-api/active_model_serializers

Muntasim Over a year ago

I just showed the process in console. He only needs the last steps

Muntasim Over a year ago

@Fire-Dragon-DoL Please look at the Update section of the question, as_json does not seem to be useful

Francesco Belladonna Over a year ago

@object.as_json(:except => ['created_at', 'updated_at'], :methods => ['dis', 'val']) and can be called directly in controller. I'm not sure if you can even use it directly on the to_json method.

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