问以嵌套形式更新many_to_many关联

EN

class User < ApplicationRecord
  has_one :profile
  has_many :specialties, through: :profile

  accepts_nested_attributes_for :profile, allow_destroy: true
end

class Profile < ApplicationRecord
  belongs_to :user
  has_many :profile_specialties
  has_many :specialties, through: :profile_specialties
end

class Specialty < ApplicationRecord
  has_many :profile_specialties
  has_many :profiles, through: :profile_specialties
end

<%= simple_form_for @user, url: wizard_path do |f| %>

  ...

  <%= simple_fields_for :profile_attributes do |cf| %>

    <%= cf.input :specialty_ids, collection: Role.order(:name), as: :grouped_select, group_method: :specialties, input_html: {multiple: true} %>

  <% end %>

  ...

<% end %>

def update
  @user = current_user
  @user.update_attributes(user_params)
  render_wizard @user
end

def user_params
  params.permit profile_attributes: [..., :specialty_ids]
end

Processing by AfterSignupController#update as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"...", "profile_attributes"=>{"specialty_ids"=>["", "22"], "commit"=>"Save and Continue", "id"=>"step_one"}
  User Load (0.7ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 ORDER BY "users"."id" ASC LIMIT $2  [["id", 52], ["LIMIT", 1]]
Unpermitted parameters: :specialty_ids
Unpermitted parameters: :utf8, :_method, :authenticity_token, :commit, :id
   (0.2ms)  BEGIN
  Profile Load (0.2ms)  SELECT  "profiles".* FROM "profiles" WHERE "profiles"."user_id" = $1 LIMIT $2  [["user_id", 52], ["LIMIT", 1]]
  SQL (0.4ms)  DELETE FROM "profiles" WHERE "profiles"."id" = $1  [["id", 110]]
  SQL (0.4ms)  INSERT INTO "profiles" ("user_id", "created_at", "updated_at") VALUES ($1, $2, $3) RETURNING "id"  [["user_id", 52], ["created_at", "2018-09-06 02:30:57.882173"], ["updated_at", "2018-09-06 02:30:57.882173"]]
   (0.5ms)  COMMIT
   (0.2ms)  BEGIN
   (0.2ms)  COMMIT
Redirected to http://localhost:3000/after_signup/requirements