Question

I’m trying to get a nested form view to update properly. This is however causing problems when the second form has existing data.

I’m using accepts_nested_attributes_for and nested_form_for. The second which only purpose is to dynamically add the form element using js. See github for more

The error I’m getting is:

Couldn't find Muscle with ID=3685340 for Exercise with ID=212831413

I’ve tried to manually do the updating but my code didnt really work and I’m under the impression that it shouldnt be needed since rails is suppose to take care of it under the hood.

The idea is that: Exercises has many Muscles through Targets
And from within the Exercise form I want to be able to add target muscles.

My models:

class Exercise < ActiveRecord::Base
  has_many :targets, :dependent => :destroy
  has_many :muscles, :through => :targets
  accepts_nested_attributes_for :muscles, :reject_if => :all_blank
  ...
end

class Target < ActiveRecord::Base
  belongs_to :exercise
  accepts_nested_attributes_for :exercise, :update_only => true
  belongs_to :muscle
end

class Muscle < ActiveRecord::Base
  has_many :targets, :dependent => :destroy
  has_many :exercises, :through => :targets
end

My (haml) view:

%p
  %b Target(s):
  = f.fields_for :muscles do |e|
    = e.collection_select :id, Muscle.all, :id, :name
    = e.link_to_remove "-remove"
  = f.link_to_add "Add target muscle", :muscles

And finally my failing controller:

  def update
    @exercise = Exercise.find(params[:id])
    @exercise.user = current_user

    params[:exercise][:muscles_attributes].each { |id, muscle|
    target = Target.where(:exercise_id => @exercise.id , :muscle_id => muscle[:id]).first
    if target && !(muscle[:_destroy] == "false")
      puts "!!>>>>>>>>>>>>>>>>>>destroy target #{target.exercise_id} #{target.muscle_id}"
      target.destroy
    else
      if !target
        t = @exercise.targets.build(:muscle_id => muscle[:id])
        t.save
      end
    end
  }

  respond_to do |format|
    if @exercise.update_attributes(params[:exercise])
      format.html { redirect_to(@exercise, :notice => 'Exercise was successfully updated.') }
      format.xml  { head :ok }
    else
      format.html { render :action => "edit" }
      format.xml  { render :xml => @exercise.errors, :status => :unprocessable_entity }
    end
  end
end

Please let me know if I should expose more of my code (the final result will be opensource anyway) ill happily push to github or whatever is requested, thanks in advance.

Answer 1

You could achieve this by manipulating the intermediate table, here targets.

Insert in your model:

accepts_nested_attributes_for :targets

And in your html, append this line with javascript:

<input name="exercise[targets_attributes][0][muscle_id]" value="the_muscle_id_goes_here" type="hidden">