Sinatra + MongoDB + JSON

sinatra_mongo_api.rb

require "sinatra"
require "mongo"
require "json"

class SimpleMongoApi < Sinatra::Base
  set :mongo, Mongo::Client.new("mongodb://my.mongo.host/database")

  def collection
    settings.mongo["things"]
  end
  
  def object
    collection.find(id_selector(params[:id]))
  end
  
  def id_selector(id)
    { _id: BSON::ObjectId.legal?(id) ? BSON::ObjectId.from_string(id.to_s) : id }
  end
  
  before do
    content_type :json
  end
  
  get '/' do
    collection.find.limit(params.fetch(:limit, 20).to_i)
  end

  post '/' do
    collection.insert_one params[:thing]
  end
    
  get '/:id' do
    object.first
  end

  put '/:id' do
    object.find_one_and_replace(params[:thing], return_document: :after)
  end
  
  delete '/:id' do
    object.find_one_and_delete
  end
end