Validate presence of polymorphic parent - ruby-on-rails

Question

I am developing a Rails 3.2 application with the following models:
class User < ActiveRecord::Base
# Associations
belongs_to :authenticatable, polymorphic: true
# Validations
validates :authenticatable, presence: true # this is the critical line
end
class Physician < ActiveRecord::Base
attr_accessible :user_attributes
# Associations
has_one :user, as: :authenticatable
accepts_nested_attributes_for :user
end
What I am trying to do is validate whether a user always has an authenticatable parent. This works fine in itself, but in my form the user model complains that the authenticatable is not present.
I am using the following controller to show a form for a new physician which accepts nested attributes for the user:
def new
#physician = Physician.new
#physician.build_user
respond_to do |format|
format.html # new.html.erb
format.json { render json: #physician }
end
end
And this is my create method:
def create
#physician = Physician.new(params[:physician])
respond_to do |format|
if #physician.save
format.html { redirect_to #physician, notice: 'Physician was successfully created.' }
format.json { render json: #physician, status: :created, location: #physician }
else
format.html { render action: "new" }
format.json { render json: #physician.errors, status: :unprocessable_entity }
end
end
end
On submitting the form, it says that the user's authenticatable must not be empty. However, the authenticatable_id and authenticatable_type should be assigned as soon as #physician is saved. It works fine if I use the same form to edit a physician and its user, since then the id and type are assigned.
What am I doing wrong here?

Answer 1

I believe this is expected:
https://github.com/rails/rails/issues/1629#issuecomment-11033182 ( last two comments).
Also check this out from rails api:
One-to-one associations
Assigning an object to a has_one association automatically saves that
object and the object being replaced (if there is one), in order to
update their foreign keys - except if the parent object is unsaved
(new_record? == true).
If either of these saves fail (due to one of the objects being
invalid), an ActiveRecord::RecordNotSaved exception is raised and the
assignment is cancelled.
If you wish to assign an object to a has_one association without
saving it, use the build_association method (documented below). The
object being replaced will still be saved to update its foreign key.
Assigning an object to a belongs_to association does not save the
object, since the foreign key field belongs on the parent. It does not
save the parent either.
and this
build_association(attributes = {}) Returns a new object of the
associated type that has been instantiated with attributes and linked
to this object through a foreign key, but has not yet been saved.
You have to create a Parent first. Then assign it's id to polymorphic object.
From what I can see, you create an object Physician.new which builds User but at this point it's not saved yet, so it doesn't have an id, so there is nothing to assign to polymorphic object. So validation will always fail since it's called before save.
In other words: In your case when you call build_user, it returns User.new NOT User.create . Therefore authenticatable doesn't have a authenticatable_id assigned.
You have several options:
Save associated user first.
OR
Move validation in to after_save callback ( Possible but very annoying and bad)
OR
Change your app structure - maybe avoid polymorphic association and switch to has_many through? Hard for me to judge since I don't know internals and business requirements. But it seems to me this is not a good candidate for polymorphic association. Will you have more models than just User that will be authenticatable?
IMHO the best candidates for polymorphic associations are things like Phones, Addresses, etc. Address can belong to User, Customer, Company, Organization, Area51 etc, be Home, Shipping or Billing category i.e. It can MORPH to accommodate multiple uses, so it's a good object to extract. But Authenticatable seems to me a bit contrived and adds complexity where there is no need for it. I don't see any other object needing to be authenticable.
If you could present your Authenticatable model and your reasoning and maybe migrations (?) I could advise you more. Right now I'm just pulling this out of thin air :-) But it seems like a good candidate for refactoring.

Answer 2

You can just move validation to before_save callback and it will work fine:
class User < ActiveRecord::Base
# Associations
belongs_to :authenticatable, polymorphic: true
# Validations
before_save :check_authenticatable
def check_authenticatable
unless authenticatable
errors[:customizable] << "can't be blank"
false
end
end
end

Answer 3

In the create action, I had to assign it manually:
#physician = Physician.new(params[:physician])
#physician.user.authenticatable = #physician
My problem is a little different (has_many and with different validation), but I think this should work.

Answer 4

I was able to get this to work by overriding the nested attribute setter.
class Physician
has_one :user, as: :authenticatable
accepts_nested_attributes_for :user
def user_attributes=(attribute_set)
super(attribute_set.merge(authenticatable: self))
end
end
To DRY it up, I moved the polymorphic code to a concern:
module Authenticatable
extend ActiveSupport::Concern
included do
has_one :user, as: :authenticatable
accepts_nested_attributes_for :user
def user_attributes=(attribute_set)
super(attribute_set.merge(authenticatable: self))
end
end
end
class Physician
include Authenticatable
...
end
For has_many associations, the same can be accomplished with a map:
class Physician
has_many :users, as: :authenticatable
accepts_nested_attributes_for :users
def users_attributes=(attribute_sets)
super(
attribute_sets.map do |attribute_set|
attribute_set.merge(authenticatable: self)
end
)
end
end
class User
belongs_to :authenticatable, polymorphic: true
validates :authenticatable, presence: true
end
All that said, I think konung's last comment is correct - your example does not look like a good candidate for polymorphism.

Answer 5

I'm not sure if this solves your problem, but I use something like this when validating that a polymorphic parent exists.
Here is some code that I used in a video model with the parent as the polymorphic association. This went in video.rb.
validates_presence_of :parent_id, :unless => Proc.new { |p|
# if it's a new record and parent is nil and addressable_type is set
# then try to find the parent object in the ObjectSpace
# if the parent object exists, then we're valid;
# if not, let validates_presence_of do it's thing
# Based on http://www.rebeccamiller-webster.com/2011/09/validate-polymorphic/
if (new_record? && !parent && parent_type)
parent = nil
ObjectSpace.each_object(parent_type.constantize) do |o|
parent = o if o.videos.include?(p) unless parent
end
end
parent
}