app.rb

require 'active_record'
require 'pg'
require 'sinatra'

ActiveRecord::Base.establish_connection(
    adapter:  'postgresql',
    host:     'localhost',
    username: 'postgres',
    password: 'postgres',
    database: 'testdb'
)

class Task < ActiveRecord::Base
  validates :name, presence: true
end

get '/' do
  @tasks = Task.all
  erb :index
  # erb :index, locals: {tasks: Task.all}
end