app.rb

require 'active_record'
require 'sinatra'
require 'json'

class User < ActiveRecord::Base
  self.primary_key = "user_id"
  has_many :messages
  has_many :memberships
end
class Message < ActiveRecord::Base
  self.primary_key = "message_id"
  belongs_to :user
end
class Channel < ActiveRecord::Base
  self.primary_key = "channel_id"
  has_many :memberships
  has_many :users, :through => :memberships
end
class Membership < ActiveRecord::Base
  self.primary_key = "membership_id"
  belongs_to :user
  belongs_to :channel
end

ActiveRecord::Base.establish_connection(
  host: "localhost",
  adapter: "postgresql",
  database: "geogossip",
  pool: 15
)

ActiveRecord::Base.include_root_in_json = false

set :public_dir, "public"

get '/channels' do
  Channel.all.map {|channel|
    channel.attributes.merge(
      users: channel.users
    )
  }.to_json
end

get '/users' do
  User.all.to_json
end

post '/users' do
  payload = JSON.parse(request.body.read) 
  user = User.create( user_nick: payload["user_nick"] )
  puts "New user: #{user.inspect}"
end