RABL filter, like Facebook Graph API

CreateComments.rb

class CreateComments < ActiveRecord::Migration
  def change
    create_table :comments do |t|
      t.string :title
      t.text :content
      t.bollean :active, default: false
      t.belongs_to :user
      t.timestamps null: false
    end
    add_index :comments, :user_id
  end
end

CreateUsers.rb

class CreateUsers < ActiveRecord::Migration
  def change
    create_table :users do |t|
      t.string :name
      t.date :birthdate
      t.bollean :active, default: false
      t.timestamps null: false
    end
  end
end

current_return.rb

[
  {
    "id": 1,
    "name": "Welington Sampaio",
    "birthdate": 01-01-1980,
    "active": true,
    "created_at": 01-08-2015,
    "updated_at": 01-08-2015,
    "comments": [
      {
        "id": 1,
        "title": "Title 1",
        "content": "Lorem ipsum ....",
        "created_at": 01-08-2015,
        "updated_at": 01-08-2015
      }
      # 500+  entries 
    ]
  },
  {
    "id": 2,
    "name": "Elison Campos",
    "birthdate": 01-01-1985,
    "active": true,
    "created_at": 10-08-2015,
    "updated_at": 10-08-2015,
    "comments": [
      {
        "id": 1502,
        "title": "Elison Title 1",
        "content": "Lorem ipsum ....",
        "created_at": 10-08-2015,
        "updated_at": 10-08-2015
      }
      # 30+  entries 
    ]
  }
  # n+ entries
]

expect_return.rb

[
  {
    "id": 1,
    "name": "Welington Sampaio",
    "birthdate": 01-01-1980,
    "comments": [
      {
        "id": 1,
        "title": "Title 1",
        "created_at": 01-08-2015
      }
      # + 9 entries 
    ]
  },
  {
    "id": 2,
    "name": "Elison Campos",
    "birthdate": 01-01-1985,
    "comments": [
      {
        "id": 1502,
        "title": "Elison Title 1",
        "created_at": 10-08-2015
      }
      # + 9 entries 
    ]
  }
  # n+ entries
]