Problem saving custom attribute in rails devise gem - ruby-on-rails

Question

The authentication system in my app is handled by devise and now I want each user in my system to belong to an organisation. So each organisation will have multiple users.
When signing up, each user will select which organisation they want to join.
When a user is signing up, and they select and organisation from a combo-box, they get the following error:
ActiveRecord::AssociationTypeMismatch in Devise::RegistrationsController#create
Organisation(#70213198483780) expected, got "1" which is an instance of String(#70213152374240)
The following is what my source code looks like:
app/models/organisation.rb
class Organisation < ApplicationRecord
has_many :users
end
app/models/user.rb
class User < ApplicationRecord
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable, :trackable and :omniauthable
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :validatable
has_many :activities
belongs_to :organisation
end
app/views/devise/registrations/new.html.erb
<h2>Sign up</h2>
<%= form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f| %>
<%= render "devise/shared/error_messages", resource: resource %>
<div class="field">
<%= f.label :email %><br />
<%= f.email_field :email, autofocus: true, autocomplete: "email" %>
</div>
<div class="field">
<%= f.label :password %>
<% if #minimum_password_length %>
<em>(<%= #minimum_password_length %> characters minimum)</em>
<% end %><br />
<%= f.password_field :password, autocomplete: "new-password" %>
</div>
<div class="field">
<%= f.label :password_confirmation %><br />
<%= f.password_field :password_confirmation, autocomplete: "new-password" %>
</div>
<div class="field">
<%= f.label :organisation %><br />
<%= f.select :organisation, Organisation.all.collect { |o| [ o.organisation_name, o.id ] }%>
</div>
<div class="actions">
<%= f.submit "Sign up" %>
</div>
<% end %>
<%= render "devise/shared/links" %>
app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
before_action :authenticate_user!
before_action :configure_sign_up_params, if: :devise_controller?
protected
# If you have extra params to permit, append them to the sanitizer.
def configure_sign_up_params
devise_parameter_sanitizer.permit(:sign_up, keys: [:organisation])
end
end

Answer 1

I suggest you should change in your form to
<%= f.select :organisation_id, Organisation.all.collect { |o| [ o.organisation_name, o.id ] }%>
Because the dropdown makes organisation.name as key and organisation.id as value.
Then change devise_parameter_sanitizer.permit(:sign_up, keys: [:organisation_id]) to allow organisation_id to be assigned to user
Instead of using collect on Organisation.all, use Organisation.all.pluck(:name, :id). It will give same result as but a more optimised query.