Rails 4升级 - attr_accessor

Question

I'm upgrading my application from rails 3.2 to rails 4.2.5.

In one of my model i have attr_accessor :user_id and i have defined a getter and setter methods, as i need to value on conditional basic.

    class DummyModel < ActiveRecord::Base

        attr_accessor :user_id
        belongs_to :current_user
        before_save :set_user_id

        def user_id
            self[:user_id] ? self[:user_id] : current_user_id ? current_user.id : nil
        end

        def user_id=(value)
            self[:user_id] = value ? value : current_user_id ? current_user.id : nil
        end

        private

        def set_user_id
            self.current_user_id = CurrentUser.first_or_create(:user_id => self[:user_id]).id
        end
    end

In the above DummyModel, that table doesn't have user_id. But a referance current_user_id which needs to be update by the params user_id which i get from browser.

So when i do DummyModel.new(params[:dummy_model]), it will try to assign the params[:dummy_model][:user_id] to the attr_accessor (With the setter method = user_id=(value)). Once assigned it can be used in the before_save.

This whole thing was working properly in rails 3.2. But when i tried to update to rails 4.2, im getting this error message, as assigning value for attr_accessor with self[:user_id] syntax is removed.

    ActiveModel::MissingAttributeError: can't write unknown attribute `user_id`

So i have one solution to rename the user_id to something else, but user_id is used is many places of my application its not possible to change.

Hope this explains my problem. Thanks for the help in advance.

Answer 1

I'm not sure why you're doing this but there's no point using attr_accessor if you're going to replace the methods it is generating. You may as well use the instance variable directly, for example

def user_id
  @user_id || current_user_id
end

def user_id=(value)
  @user_id = value || current_user_id
end

Answer 2

If you prefer attr_accessible, you could use it in Rails 4 too. You should install it like gem:

gem 'protected_attributes'

What i can understand from the above but in rails 4 now there are strong parameters. attr_accessor still can be initialized in rails 4 and that still gives you virtual attributes, but from above it looks like user_id is a physical attribute on the model level. Let me know if this makes sense.

Answer 3

I think you are confused about rails 3 attr_accessible and attr_accessor .

Link about difference between them: https://stackoverflow.com/a/6958433/1306709

In rails 4 you still can use attr_accessor , but if you meant attr_accessible here is some info: strong parameters