Validation on a has_many relationship in rails 3.2
rails-activerecord, ruby-on-rails, ruby-on-rails-3.2
Solution
You can use "validates_presence_of"
class User < ActiveRecord::Base
has_many :sports
validates_presence_of :sports
end
But there is a bug with it if you will use `accepts_nested_attributes_for` with `:allow_destroy => true`.
You can look into this : Nested models and parent validation
Problem
Given that I have the next models: user.rb ``` has_many :favorites, dependent: :destroy has_many :sports, through: :favorites ``` sport.rb ``` has_many :favorites, dependent: :destroy has_many :users, through: :favorites ``` In the form for create a new user, there is a list of checkboxes of sports, and in the user validation I want to validate that at least one is selected. I'm doing it like this: In the user controller create action: ``` @user = User.new(params[:user]) @user.sports << Sport.find(params[:sports]) unless params[:sports].nil? if @user.save ... ``` In the user model ``` validate :user_must_select_sport def user_must_select_sport if sports.empty? errors.add(:Sport, "You have to select at least 1 sport") end end ``` And it's actually working, but I'm guessing that it has to be a better way of doing this. I'd appreciate any help.