Question

I’m using the nested_form gem for my AddressBook relation. When the user blanks out the value of an existing Addr, I want to delete that Addr rather than saving with a blank value

class Person < ActiveRecord::Base
  has_many :addrs, dependent: :destroy
  attr_accessible :name, :addrs_attributes
  accepts_nested_attributes_for :addrs, reject_if: :addr_blank, allow_destroy: true

  def addr_blank(a)
    valid? && a[:id].blank? && a[:value].blank? 
  end

class Addr < ActiveRecord::Base
  belongs_to :person
  attr_accessible :kind, :label, :value, :person_id

My :reject_if method works well but it doesn’t give me everything I need

1. valid? keeps my blank Addrs around through validation
2. a[:id].blank? avoids rejections when the user blanks out and existing record

Now, I need to delete (rather than save) an existing Addr when the user blanks the value. Also, I’m exposing Persons and Addrs via a RESTful API. I see two possible options:

1. Post process the params hash to add the magical _destroy=1 param. IOW, emulate the user activity of pressing the delete button.
2. Encapsulate this inside the Addr model such that an update with a blank value is effectively considered a delete.

Based on the advice here is how I implemented it:

people_controller.rb

def update
  @person = Person.find(params[:id])
  @person.destroy_blank_addrs(params[:person])
  respond_to do |format|
  ...

person.rb

def destroy_blank_addrs(person_params)
  if valid? && person_params[:addrs_attributes]
    person_params[:addrs_attributes].each do |addr_params_array|
      addr_params= addr_params_array[1] 
      addr_params[:_destroy] = '1' if !addr_params[:id].blank? && addr_params[:value].blank? 
    end
  end
end

Answer 1

A third alternative would be to add an before_save callback on Person that will remove all addresses that are blank. This idea has some merit, but I probably won’t go with it.

Out of the two options you present, I will not go with post-processing the params. It will work out, but it is too much work. Besides, to controller code will get a bit messier and I’m a firm believer in a very slim controller.

The easiest option, in my head, is to remove the blank addresses after saving. You can add Person#remove_blank_addresses() and then call it on successful save. You don’t need to pass in the params – it can just iterate the addresses and remove the blank ones. It has the disadvantage of creating empty addresses and then destroying them, but you would need that for updating people anyway.

If we’re talking about the cleanest solution (in my opinion), I would introduce a third class that would handle all that logic and have the controller delegate to it. The controller would be easy enough to test in isolation and then you can write a model spec that checks all the nitty-gritty details. It is a bit more work and I can’t think of a good name right now (PersonUpdater?), but it might be an idea worth thinking about.