How to make sure child object is valid while saving parent? - ruby-on-rails

Question

let say that I have two class
class User
attr_accessible :name
has_one :address
validates :name, :presence => true
validates_associated :address
end
class Address
attr_accessible :country, :user_id
belongs_to :user
validates :country, :presence => true
validates :user, :presence => true
end
Now when i try to create invalid Address then it fails(which is good)
a = Address.new
a.valid? #=> false
But when i build User with invalid Address then it pass(which is bad)
u = User.first
u.build_address
u.valid? #=> true
u.save #=> true
Due to this User has Address with country => nil.
How can i tell Rails to not save Address if its invalid?
FIXED: I fixed this by adding follow line to the code. Thank you everyone.
validates_associated :address, :if => :address

Answer 1

class User
attr_accessible :name
has_one :address, :validate => true
validates :name, :presence => true
validates_associated :address
end

Answer 2

You need to also validate that an Address is actually present for User:
class User < ActiveRecord::Base
validates :address, :associated => true, :presence => true
end
With that in place, I get:
>> u = User.first
=> #<User id: 1, name: "Bob", created_at: "2013-10-09 15:17:21", updated_at: "2013-10-09 15:17:21">
>> u.build_address
=> #<Address id: nil, user_id: 1, country: nil, created_at: nil, updated_at: nil>
>> u.valid?
=> false
>> u.errors
=> #<ActiveModel::Errors:0x007fe1d6919b18 #base=#<User id: 1, name: "Bob", created_at: "2013-10-09 15:17:21", updated_at: "2013-10-09 15:17:21">, #messages={:address=>["is invalid"]}>
>> u.address.errors
=> #<ActiveModel::Errors:0x007fe1d69197a8 #base=#<Address id: nil, user_id: 1, country: nil, created_at: nil, updated_at: nil>, #messages={:country=>["can't be blank"]}>