ruby on rails web app controller generates error

Question

I am following along a video series, where the author is creating a simple CMS using RoR 4, but I currently have RoR 3.x installed. I followed all the code to a "T" but when I try to create a simple subject in the simple CMS, I am getting an error. So I checked the log/production.log

And I am getting the following error, TypeError (no implicit conversion of Symbol into String):

The controller code looks like the following,

def create
    # Instantiate a new object using form parameters

    # the below line should work with rails v3.x
    # @subject = Subject.new(params[:subject])

    @subject = Subject.new(subject_params)

    # Save the object
    if @subject.save
      # add flash hash
      flash[:notice] = "Subject created successfully."
      # if save succeeds, redirect to the index action
      redirect_to(:action => 'index')
    else
      # if save fails, redisplay the form so user can fix problems
      render('new')
    end
  end

And the private method I created for the subject new params looks like the following

 private

    def subject_params
      # same as using "params[:subject]", except that it:
      # - raises an error if :subject is not present
      # - allows listed attributes to be mass-assigned
      params.require(:subject).permit(:name, :position, :visible)
    end

Answer 1

The author tells you that you need to change @subject = Subject.new(subject_params) to @subject = Subject.new(params[:subject]).

params.require(:subject).permit(:name, :position, :visible) is a Rails 4 feature called Strong Parameters. If you are new to Rails I would suggest you use the version the author uses to alleviate future version issues like this.