Rails form associations for simple_form

Question

Hi I am having trouble with creating association using simple_form. Model Chapter belongs to Subject:

class Subject < ActiveRecord::Base

  validates :name, :presence => true,
                                    :length => {:maximum => 30},
                                    :uniqueness => true  

  has_many :chapters    

end

Model for Chapter:

class Chapter < ActiveRecord::Base

  validates :name, :presence => true,
                                    :length => {:maximum => 80}

  validates :subject_id, :presence => true

  belongs_to :subject

end

Controller for Chapter

  def new
    @chapter = Chapter.new
  end

  def create
    @chapter = Chapter.new(chapter_params)
    if @chapter.save
      flash[:notice] = "Chapter created successfully."
      redirect_to(:action => 'index')
    else
      render('new')
    end
  end

  private

  def chapter_params
    params.require(:chapter).permit(:name, :permalink, :subject_id, 
                                  :introduction, :free, :active, :position, :semester)
end

Form for new Chapter

  <%= simple_form_for(:chapter, :url => {:action => 'create'} ) do |f| %>

    <%= f.input :name %>
    <%= f.input :permalink} %>


    <%= f.association :subject %>


    <%= f.input :introduction %>
    <%= f.input :free, as: :radio_buttons%>
    <%= f.input :active, as: :radio_buttons %>
    <%= f.input :position %>
    <%= f.input :semester %>

    <%= f.button :submit, value: 'Save Chapter' %>

I get following error:

"Association cannot be used in forms not associated with an object."

Is there anything I need to add to my controller or model? When I don't use association and simply input the ID of subject, everything works.

Answer 1

You need to add to the Chapter model the following code

accepts_nested_attributes_for :subject

Update

Since the Subject Model is the parent of the Chapter model, the solution described before won't work. accepts_nested_attributes_for only works in the "has_many" model and not in the "belongs_to" model. I'm leaving it here for reference.

In order to make the form builder know how about the association, you need to add to your controller "new" method the following code:

@chapter.build_subject

You will also need to change the simple_form_for call from:

simple_form_for(:chapter, :url => {:action => 'create'} ) do |f|

to:

simple_form_for @chapter do |f|

Because you need to pass the object you created to your form, and you're not doing that using a symbol in the simple_form_for call.