Rails Object Relationships and JSON Rendering

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By default you’ll only get the JSON that represents modelb in your example above. But, you can tell Rails to include the other related objects as well:

def export
  @export_data = ModelA.find(params[:id])
  respond_to do |format|
    format.html
    format.json { render :json => @export_data.to_json(:include => :modelb) }
  end
end

You can even tell it to exclude certain fields if you don’t want to see them in the export:

render :json => @export_data.to_json(:include => { :modelb => { :except => [:created_at, updated_at]}})

Or, include only certain fields:

render :json => @export_data.to_json(:include => { :modelb => { :only => :name }})

And you can nest those as deeply as you need (let’s say that ModelB also has_many ModelC):

render :json => @export_data.to_json(:include => { :modelb => { :include => :modelc }})

If you want to include multiple child model associations, you can do the following:

render :json => @export_data.to_json(include: [:modelA, :modelB, :modelN...])

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