Forum: Ruby on Rails nested forms - how to use before/after destroy callback ?

How is it possible to use a callback and which one to avoid the 
destroying
of the last association.
For example, there are 3 following models:

#timesheet.rb
class Timesheet < ActiveRecord::Base
  has_many :activities, dependent: :destroy
  has_many :time_entries, through: :activities
  accepts_nested_attributes_for :activities, allow_destroy: true
end

#activity.rb
class Activity < ActiveRecord::Base
  has_many :time_entries, order: :workdate, dependent: :destroy
  accepts_nested_attributes_for :time_entries, allow_destroy: true,
reject_if: proc { |a| a[:worktime].blank? }
end

#time_entry.rb
class TimeEntry < ActiveRecord::Base
  belongs_to :activity
  validates :worktime, presence: true, inclusion: { in: [0.5, 1] }
end

Every timesheet is created for 7 days (tile_entries) for one activity in
the the same form. To delete I use the technic with jQuery explained at
Railscats:
#add_remove_fields.js

function remove_fields(link) {
  $(link).prev("input[type=hidden]").val("1");
  $(link).closest(".fields").hide();
}

function add_fields(link, association, content) {
  var new_id = new Date().getTime();
  var regexp = new RegExp("new_" + association, "g");
  $(link).parent().before(content.replace(regexp, new_id));
}

#application_helper.rb

def link_to_remove_fields(name, f)
    f.hidden_field(:_destroy) + link_to_function(name,
"remove_fields(this)")
  end

  def link_to_add_fields(name, f, association, timesheet)
...
end

I tried several ways with after_destroy hook, - it didn't work.
Any idea ? Thanks and regards.

So still no idea how to avoid the destroy of the last association. I do 
all
the processing in the 'update ' action of TimesheetsController. I tried
with 'after_update' hook in the Timsheet model as follows:

#timesheet.rb
class Timesheet < ActiveRecord::Base
  accepts_nested_attributes_for :activities, allow_destroy: true
  after_update :check_an_activity_present

  private
    def check_an_activity_present
      raise "You should have at least ONE activity present" if
activities.empty?
    end
end

An I put the update_attributes in the begin/rescue block in the 
controller:
#timesheets_controller.rb
class TimesheetsController < ApplicationController
def update
    begin
      @timesheet = current_user.timesheets.find(params[:id])
      if @timesheet.update_attributes(params[:timesheet])
        flash[:success] = 'Timesheet updated sucessfully'
        redirect_to @timesheet
      else
        load_entries
        render 'edit'
      end
    rescue Exception => e
      flash.now[:error] = e.message
      @entries = @timesheet.time_entries
      render 'edit'
    end

private
  def load_entries
      @entries = @timesheet.build_and_sort_time_entries
    end
  end
end

The problem is that the activity with corresponding time entries 
collection
is not destroyed even if I added a new activity with corresponding time
entries. So after the update executed, I have 2 activities saved with
corresponding time entries instad of having just the ONLY one, entered 
just
after the destroying the previous one. Any idea? Thank you.

Finally, after_update callback works as needed, te problem was in the 
new
fields_for generation. The below is the correct and updated version:

#timesheet.rb
> reject_if: proc { |a| a[:worktime].blank? }
>
    validate :one_time_entry_present
private
    def one_time_entry_present
      errors[:base] << "At least one entry should be entered" if
time_entries.empty?
    end

> Railscats:
>   var regexp = new RegExp(association_id, "g");
>  def link_to_add_fields(name, f, association, timesheet)
>     link_to_function(name, "add_fields(this, \"#{id}\",
> \"#{escape_javascript(fields)}\")")
>   end
>

#timesheets_controller.rb

def update
    begin
      @timesheet = current_user.timesheets.find(params[:id])
      if @timesheet.update_attributes(params[:timesheet])
        flash[:success] = 'Timesheet updated sucessfully'
        redirect_to @timesheet
      else
        load_entries
        render 'edit'
      end
    rescue Exception => e
      flash[:error] = e.message
      redirect_to edit_timesheet_path(@timesheet)
    end

  end

Hope this helps.