Instance variable value is not changed in application controller

Question

I already found a workaround for my problem, but I still don't get why this problem occurs. I think i am missing some things about how internals working.

I am calling *check_modify_rights* method from couple of controllers, and I want to have a variable with appropriate name (@post for post_controller instead of a generic one, like @object)

So after before_filter runs, I expect to have a @post instance variable with a Post model. But I get a new Post model (because of @post = Post.new), and when I checked object_id s in the method, they are different.

# post_controller
  before_filter do |f|
    @post = Post.new
    f.check_modify_rights @post
  end

# application_controller
  def check_modify_rights(obj)
    return redirect_to login_path, :notice => "Please login" unless @user

    p obj.object_id
    obj = obj.class.find(params[:id])
    p obj.object_id

    return if obj.user.id == @user.id or @user.is_admin?

    redirect_to posts_path, :notice => "You don't have permission for this action"
  end
end

Obviously @post = Post.new will have a different id from a newly instantiated object — apneadiving
– apneadiving, Commented Dec 30, 2012 at 18:00
Yeah I can see that, but I am only changing obj 's value, and since @answer variable is a pointer to actual value, I expected to change its value. Am I wrong? — tackleberry
– tackleberry, Commented Dec 30, 2012 at 18:03
Nope, you instantiate a new object when you do obj = obj.class.find(params[:id]) — apneadiving
– apneadiving, Commented Dec 30, 2012 at 18:04
Damn! you are right of course. I thought obj just like pointer and expected it points the same memory region as @answer, thus I thought @answers's value also should be changed when value changed that obj points. — tackleberry
– tackleberry, Commented Dec 30, 2012 at 18:09

apneadiving · Accepted Answer · 2012-12-30 18:25:23Z

1

Obviously @post = Post.new will have a different id from a newly instantiated object.

To retrieve the new object you could:

1) use a generic instance variable: @resource = Post.new

2) or:

# in your before filter
@post = f.check_modify_rights @post
# in application controller
return obj if obj.user.id == @user.id or @user.is_admin?

But basically, you're redoing Cancan, which I'd not recommend.

answered Dec 30, 2012 at 18:25

apneadiving

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1 Comment

tackleberry Over a year ago

thanks! I didn't notice return **obj** if obj.user.id == @user.id or @user.is_admin?

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