ruby on rails - "WARNING: Can't mass-assign protected attributes"

Question

I have used RESTful techniques to generate a model (in fact, I am using Devise gem, which does that for me), and I have added new fields called first_name and last_name to the model. Migration went fine. I added attr_accessor :first_name, :last_name to the model and expected it would just work. But when I try to mass-assign new instances with Doctor.create({:first_name=>"MyName"}) etc., I am getting errors saying I can't mass-assign protected attributes.

I thought the whole point of using attr_accessor was to get around the protectedness of the fields of a model. Can you help me make sense of this message?

Edit: oh, and by the way the records do not get created either. I thought they should be since this is just a warning, but they are not on the database.

Edit2: here is my model

class Doctor < User
  has_many :patients
  has_many :prescriptions, :through=> :patients

  validates_presence_of :invitations, :on => :create, :message => "can't be blank"

  attr_accessor :invitations
end

and the schema, which doesn't have the first_name and last_name because they are created in the users table, which is the ancestor of doctors. I used single table inheritance.

create_table :doctors do |t|
  t.integer :invitations

  t.timestamps
end

and this is the migration to change the users table

add_column :users, :first_name, :string
add_column :users, :last_name, :string
add_column :users, :type, :string

EDIT: here is the seed file. I am not including the truncate_db_table method, but it works.

%w{doctors patients}.each do |m|
  truncate_db_table(m)  
end  

Doctor.create(:invitations=>5, :email=>"email@gmail.com", :first_name=>"Name", :last_name=>"LastName")
Patient.create(:doctor_id=>1, :gender=>"male", :date_of_birth=>"1991-02-24")

Answer 1

Don't confuse attr_accessor with attr_accessible. Accessor is built into Ruby and defines a getter method - model_instance.foo # returns something - and a setter method - model_instance.foo = 'bar'.

Accessible is defined by Rails and makes the attribute mass-assignable (does the opposite of attr_protected).

If first_name is a field in your model's database table, then Rails has already defined getters and setters for that attribute. All you need to do is add attr_accessible :first_name.