Active Model Serializers: Adding extra information outside root in ArraySerializer

Question

Say I have a model User and a serializer UserSerializer < ActiveModel::Serializer, and a controller that looks like this:

class UsersController < ApplicationController
  respond_to :json
  def index
    respond_with User.all
  end
end

Now if I visit /users I'll get a JSON response that looks like this:

{
  "users": [
    {
      "id": 7,
      "name": "George"
    },
    {
      "id": 8,
      "name": "Dave"
    }
    .
    .
    .
  ]
}

But what if I want to include some extra information in the JSON response that isn't relevant to any one particular User? E.g.:

{
  "time": "2014-01-06 16:52 GMT",
  "url": "http://www.example.com", 
  "noOfUsers": 2,
  "users": [
    {
      "id": 7,
      "name": "George"
    },
    {
      "id": 8,
      "name": "Dave"
    }
    .
    .
    .
  ]
}

This example is contrived but it's a good approximation of what I want to achieve. Is this possible with active model serializers? (Perhaps by subclassing ActiveModel::ArraySerializer? I couldn't figure it out). How do I add extra root elements?

Answer 1

You can pass them as the second arguement to respond_with

def index
 respond_with User.all, meta: {time: "2014-01-06 16:52 GMT",url: "http://www.example.com", noOfUsers: 2}
end

In version 0.9.3 in an initializer set ActiveModel::Serializer.root = true:

ActiveSupport.on_load(:active_model_serializers) do
  # Disable for all serializers (except ArraySerializer)
  ActiveModel::Serializer.root = true
end

In controller

render json: @user,  meta: { total: 10 }

Answer 2

Got it working using render:

render json: {
  "time": "2014-01-06 16:52 GMT",
  "url": "http://www.example.com", 
  "noOfUsers": 2,
  "users": @users
}

The problem is, this doesn't call UserSerializer, it just calls .as_json on each individual user object and skips the Serializer. So I had to do it explicitly:

def index
  .
  .
  .
  render json: {
    "time": "2014-01-06 16:52 GMT",
    "url": "http://www.example.com", 
    "noOfUsers": 2,
    "users": serialized_users
  }
end

def serialized_users
  ActiveModel::ArraySerializer.new(@users).as_json
end

Not the most elegant solution but it works.