Question

I can create a record with the correct association using the create method, but if I use build then save the instance, It doesn’t create the association.

this works

@account = Account.find(params[:id])  
@user = @account.users.create!(:profile_attributes => { name:  name, company: company_name },email: email, password: password, password_confirmation: password)

but this will only create the user and not the association to the account, which is through a polymorphic membership model

@account = Account.find(params[:id])  
@user = account.users.build(:profile_attributes => { name:  name, company: company_name },email: email, password: password, password_confirmation: password)
@user.save

I want to use save so that I can use all the validations and callbacks on this.

membership.rb

class Membership < ActiveRecord::Base

  belongs_to :target, polymorphic: true
  belongs_to :user
  belongs_to :team

  validates :target, presence: true
  validate  :has_user_or_team

  module HasMembersMixin
    extend ActiveSupport::Concern

    included do
      has_many :memberships,  as: :target
      has_many :users, through: :memberships
    end
    module ClassMethods
      def accessible_by(user)
        conditions = Membership.arel_for_user_or_their_teams(user)
        if direct_conditions = directly_accessible_by(user)
          conditions = conditions.or(direct_conditions)
        end
        includes(:memberships).where conditions
      end
    end
end

module methods excluded

class Account < ActiveRecord::Base
   include Membership::HasMembersMixin
end

Answer 1

Ah, now I realized. So, the thing is, when you create an AR instance, the associations which are not stored will be all saved. This is the default creation behaviour: save everything. But, if a record already exists, the changes on its associations made using it will not persist. Let’s say an account as a user, and this is an example:

Account.new(:user => User.new) # this saves the account and the user
a = Account.find(params[:id]); a.user.name = "Boris Karloff" ; a.save # this will not store the user name

So, this is default AR behaviour, there’s not much you can do. You can set :autosave => true on the association, but I wouldn’t recommend it (each time you would save an account, it would also always try to save all users, even though you hadn’t made any changes to them). It’s, let’s just say, a feature bug 🙂