How do you set a has_one default value in ActiveRecord?

I have something like this:

class User < ActiveRecord::Base
  has_one :profile
end

class Profile < ActiveRecord::Base
  belongs_to :user
end

user = User.new
user.profile.something #=> ERROR

What is a proper way to set a default profile object in this case? I have tried this:

class User < ActiveRecord::Base
  default_scope :include => :profile
  has_one :profile

  def after_initialize
    self.profile ||= Profil开发者_开发问答e.new(:user => self)
  end
end

...but that creates N+1 queries. Any ideas?

Update

This is what I have now, works okay, still looking for something better:

class User < ActiveRecord::Base
  default_scope :include => :profile
  has_one :profile, :autosave => true

  def after_initialize
    self.profile = Profile.new(:user => self) if new_record?
  end
end

This way, you're going to have a Profile whenever you finally create your user. Otherwise, the only case is a new_record?.

---

You can write your own User#profile that will build one for you if it doesn't exist:

class User < ActiveRecord::Base
  has_one :profile

  def profile_with_default
    profile_without_default || build_profile
  end
  alias_method_chain :profile, :default
end

---

This is a good answer:

class User < ActiveRecord::Base
 has_one :preference_set

 def preference_set
   super || build_preference_set
  end
end

---

I think your answer is good. I've got a slightly different solution:

class User < ActiveRecord::Base
  default_scope :include => :profile
  has_one :profile
  alias_method :my_profile, :profile

  def my_profile
    self.profile = Profile.create(:user => self) unless self.profile
    self.profile
  end
end

Good

• create profile when requested, not on instantiation

Not so good

• You have to use my_profile (or however you would like to call it)
• The unless self.profile check has to be done on each profile call

---

The correct answer relies on what are your intentions, cause there is no straight forward solution to this kind of problem.

The after_initialize callback is called after object is instantiated, so it's not really a good place for this kind of logic.

Maybe you should try to use before_create / after_create instead? Those callbacks are called only at object creation time.

Also, don't use Profile.new, use one of the methods below instead:

self.build_profile(...)
self.create_profile(...)

In the 2nd case the model is being saved. You can pass a hash with model attributes to both methods (don't pass :user, as it is set automatically).