Question

I have a nested Form

A Crew can have many meetings, a Meeting can belong to one Crew.
A Crew, and a Meeting can both have set a gender_id attribute.

I want to add an error to the Meeting object when Crew.meeting_id != Meeting.gender_id

I have written a simple validator

class MeetingGenderValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    if record.gender_id != record.crew.gender_id
      msg = :wrong_gender
      case record.crew.gender_id
        when 1 then
          msg = :crew_woman_only
        when 2 then
          msg = :crew_man_only
        record.errors.add(attribute, msg, options)
      end
    end
  end 
end

The problem is, When this validator is run, The record variable (our Meeting model), is not yet associated with the Crew model, so I get an error on calling Nil.gender_id

Here is the part of Meeting model:

class Meeting < ActiveRecord::Base
  belongs_to :crew 
  validates :gender_id, :meeting_gender => true
end

Here is the part of Crew model with the association:

class Crew < ActiveRecord::Base
  has_many :meetings
  accepts_nested_attributes_for :meetings
end

And my Crews#Create action snippet (controller):

class CrewsController < ApplicationController
  def create
    @crew = Crew.new(params[:crew]) # here are the meeting params too
    @crew.user = current_user # assigning the user from session / not important here
    if @crew.save
      ......
  end
end

Answer 1

Have found a workaround, in the Crews controller:

def create
  @crew = Crew.new(params[:crew])
  if @crew.meetings.to_a.size > 0
    @meeting = @crew.meetings.first
    @meeting.crew = @crew
    @crew.meetings = [] 
    @crew.meetings << @meeting
  end
  @crew.user = current_user
  ....
end

I now, it’s not pretty, but it works, it can be delegated to a model method, but I want show here a working solution. The question is still open…