Ruby on Rails - Render JSON for multiple models

Question

I am trying to render results from more than one model in JSON. The following code in my controller only renders the first result set:

  def calculate_quote
    @moulding = Moulding.find(params[:id])
    @material_costs = MaterialCost.all

    respond_to do |format|
      format.json  { render :json => @moulding }
      format.json  { render :json => @material_costs }
    end
  end

Any help would be much appreciated, thanks.

score 93 · Accepted Answer · answered Nov 30 '10 at 21:48

One way you could do this is to create a hash with the objects you want to render, and then pass that to the render method. Like so:

respond_to do |format|
  format.json  { render :json => {:moulding => @moulding, 
                                  :material_costs => @material_costs }}
end

If the models aren't associated through active record, that's probably your best solution.

If an association does exist, you can pass an :include argument to the render call, like so:

respond_to do |format|
  format.json  { render :json => @moulding.to_json(:include => [:material_costs])}
end

Note that you wouldn't have to retrieve the @material_costs variable in the section above if you take this approach, Rails will automatically load it from the @moulding variable.

Used your suggestion as well after finding this post. My models do have an association but I went with your first example as I feel it reads better. Thank you! — Tass, Mar 28 '12 at 18:40

score 8 · Answer 2 · answered Nov 30 '10 at 21:52

A controller can only return one response. If you want to send all these objects back, you have to put them in one JSON object.

How about:

def calculate_quote
  @moulding = Moulding.find(params[:id])
  @material_costs = MaterialCost.all
  response = { :moulding => @moulding, :material_costs => @material_costs }
  respond_to do |format|
    format.json  { render :json => response }
  end
end

score 2 · Answer 3 · answered Dec 31 '11 at 15:00

I did something like

respond_to do |format|
      format.html # show.html.erb
      format.json { render :json => {:cancer_type => @cancer_type, :cancer_symptoms => @cancer_symptoms }}

here is the result

{"cancer_type":{"created_at":"2011-12-31T06:06:30Z","desc":"dfgeg","id":2,"location":"ddd","name":"edddd","sex":"ddd","updated_at":"2011-12-31T06:06:30Z"},"cancer_symptoms":[]}

So it is working

Thank you guys

score 0 · Answer 4 · answered Feb 04 '21 at 18:22

Not seeing a more complex example I wanted to throw in the following.

  def calculate_quote
    moulding = Moulding.find(params[:id])
    material_costs = MaterialCost.all

    respond_to do |format|
      # there times you'll need multiple formats, no need to overuse instance vars:
      format.html do
        @moulding = moulding
        @material_costs = material_costs
      end
      format.json do
        # in case of as_json, you can provide additional options 
        # to include associations or reduce payload.
        moulding_json = moulding.as_json
        material_costs_json = material_costs.as_json
        render json: {
           moulding: moulding_json,
           material_costs: material_costs_json 
        }
      end
    end
  end

Ruby on Rails - Render JSON for multiple models

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