How to delete child during update with reject_if option for accepts_nested_attributes_for

Question

I am on Rails 5.0. I'm not quite sure if this should work or if I need to take a different approach. I have models for Procedure and Complication where Procedure has_many Complications defined like so;

class Procedure < ActiveRecord::Base
  has_many :complications, dependent: :destroy
  accepts_nested_attributes_for :complications, allow_destroy: true, reject_if: proc{|attr| attr[:name] == 'None'}
end

class Complication < ActiveRecord::Base
  belongs_to :procedure
  validates :name, presence: true
end

The user is presented with a nested form for the procedure with multiple complications. I have used the cocoon gem to do this dynamically. On a new record the user is presented with an empty complication select box. If they leave it empty the validation fails. This is to force them to select 'None' in order to prevent them skipping the field. If they do select 'None' then no complication is added because of the reject_if option. All of this works exactly as expected.

The problem I have arises if a complication is selected (e.g. 'Failed') and the procedure record is subsequently edited. If the complication is changed to 'None' and then the record is updated, the complication will be left unchanged (i.e. still 'Failed') when the behaviour I want is for the complication to be destroyed.

Presumably the reject_if option doesn't function to delete a record on an update if it already exists. Is this correct? If so, what is the appropriate way of handling my case?

TIA.

Answer 1

What you want is kind of out of the scope for the reject_if option.

You should be able to get the functionality by altering the whitelisted params to add _destroy = '1' if the name is "None" (or blank or nil).

class ProceeduresController

  # ...

  def update
     
  end

  private
    # ...
    # Only allow a trusted parameter "white list" through.
    def proceedure_params
      params.require(:proceedure)
            .permit(:name,complications_attributes: [:id, :name, :_destroy])
    end

    def update_params
      proceedure_params.tap do |p|
         p["complications_attributes"].each do |a|
           if a[:id].present? &&  ["None", nil, ""].includes?(a[:name])
             a[:_destroy] = '1'
           end
         end
       end
    end
end

---

class Procedure < ActiveRecord::Base
  has_many :complications, dependent: :destroy
  accepts_nested_attributes_for :complications, 
    allow_destroy: true, 
    reject_if: :reject_attributes_for_complication?

  def reject_attributes_for_complication?(attr)
    return false if attr[:_destroy]
    attr[:name] == 'None'
  end
end