Question:

I have tableless model (like it was shown in #219 railscast):

class MyModel include ActiveModel::Conversion extend ActiveModel::Naming attr_accessor :attr1, :attr2, :attr3, :attr4 private def initialize(attr1 = nil) self.attr1 = attr1 end def persisted? false end end

Then I'm trying to render JSON in controller:

@my_model = MyModel.new render json: @my_model.to_json(only: [:attr1, :attr2])

but it renders JSON with all the attributes of the model.

I've tried to add

include ActiveModel::Serialization

but it didn't change rendered JSON.

How can I render JSON with only necessary attributes of my tableless model?

I'm using Rails 3.2.3

<strong>Update</strong>

Thanks, guys. It seems you're all almost right. I combined your solutions and got this:

Model:

include ActiveModel::Serialization ... def to_hash { attr1: self.attr1, attr2: self.attr2, ... } end

Controller:

render json: @my_model.to_hash.to_json(only: [:attr1, :attr2])

I really don't know whose answer to be accepted.

<strong>Update 2</strong>

Suddenly new strangeness appeared. One of the attributes is array of hashes. It was like this:

attr1: [[{name: "name", image: "image"}, {name: "name", image: "image"}], [{name: "name", image: "image"}, {name: "name", image: "image"}]]

But now it lost all its content and looks like this:

attr1: [[{}, {}], [{}, {}]]

Maybe anyone know how to fix it?

<strong>Update 3</strong> :)

Erez Rabih's answer helped. Using slice instead of to_json solved the problem. So, final solution is:

render json: @my_model.to_hash.slice(:attr1, :attr2)

I know it isn't straight forward but how about:

render :json => @my_model.attributes.slice(:attr1, :attr2)

You will also be required to define an attributes method as:

def attributes {:attr1 => self.attr1.....} end

Thanks for the comment bender.

I believe it's because Object::as_json is calling internally (look at this: <a href="http://apidock.com/rails/Object/as_json" rel="nofollow">http://apidock.com/rails/Object/as_json</a>), and it has no options like :only or :except, so you can overide method to_hash in your class, e.g.:

def to_hash {:attr1 => self.attr1, :attr2 => self.attr2} end

and to_json will do exactly what you want.

Certainly, another option is to override method to_json ...

You may mix your initial approach (including AM serialization modules) with Erez' one as the <a href="http://api.rubyonrails.org/classes/ActiveModel/Serialization.html" rel="nofollow">documentation</a> suggests.

class MyModel include ActiveModel::Serialization::JSON .... def attributes {:attr1 => self.attr1.....} end ... end