```ruby
class Address < ActiveRecord::Base
  belongs_to :user
  validates :state, length: { maximum: 2 }
end
```

Add some validations to Address model
user
```ruby
class Address < ActiveRecord::Base
  belongs_to :user
  validates :state, length: { maximum: 2 }
  validates :user_id, :city, :state, :zip_code, presence: true
end
```
assistant