class Micropost <ActiveRecord::Base
　　validates :content, length:{ maximum:140 }
end

class Micropost <ActiveRecord::Base
　　validates :content, length:{ maximum:140 } ,presence: true
end

class User <ActiveRecord::Base
　　has_many :microposts
end

class Micropost <ActiveRecord::Base
　　belongs_to :user
　　validates :content, length:{ maximum:140 }
end

$ rails console
>> first_user = User.first
>> first_user.microposts
>> micropost = first_user.microposts.first
>> micropost.user
>> exit

$ git status 
$ git add -A
$ git commit -m "Finish toy app"
$ git push
$ git push heroku
$ heroku run rake db:migrate