Rails has_many :through association: save instance into join table -

in our rails app, there 3 models:

class user < activerecord::base   has_many :administrations, dependent: :destroy   has_many :calendars, through: :administrations end  class administration < activerecord::base   belongs_to :user   belongs_to :calendar end  class calendar < activerecord::base   has_many :administrations, dependent: :destroy   has_many :users, through: :administrations end 

and here corresponding migrations:

class createusers < activerecord::migration   def change     create_table :users |t|       t.string :first_name       t.string :last_name       t.string :email        t.timestamps null: false     end   end end  class createadministrations < activerecord::migration   def change     create_table :administrations |t|       t.references :user, index: true, foreign_key: true       t.references :calendar, index: true, foreign_key: true       t.string :role        t.timestamps null: false     end   end end  class createcalendars < activerecord::migration   def change     create_table :calendars |t|       t.string :name        t.timestamps null: false     end   end end 

we have created calendar#create action follows:

def create     @calendar = current_user.calendars.build(calendar_params)     if @calendar.save       flash[:success] = "calendar created!"       redirect_to root_url     else       render 'static_pages/home'     end   end 

and corresponding _calendar_form.html.erb partial:

<%= form_for(@calendar) |f| %>   <%= render 'shared/error_messages', object: f.object %>   <div class="field">     <%= f.text_field :name, placeholder: "your new calendar name" %>   </div>   <%= f.submit "post", class: "btn btn-primary" %> <% end %> 

this "works" since, when create new calendar through form, show in rails console, when type calendar.all.

however, seems no new @administration being created , administration table not updated, nothing returns when type administration.all in console.

we thought administration table, join table between user table , calendar table, , respectively contains user_id , calendar_id columns, updated automatically when creating new calendar.

how can achieve this? need create specific administration#create action?

update: based on comments , answers, implemented following calendarscontroller:

class calendarscontroller < applicationcontroller    def create     @calendar = current_user.calendars.build(calendar_params)     if @calendar.save       current_user.administrations << @calendar       @calendar.administration.role = 'creator'       flash[:success] = "calendar created!"       redirect_to root_url     else       render 'static_pages/home'     end   end  ... 

however, returns following error:

activerecord::associationtypemismatch in calendarscontroller#create  unless record.is_a?(reflection.klass) || record.is_a?(reflection.class_name.constantize)             message = "#{reflection.class_name}(##{reflection.klass.object_id}) expected, got #{record.class}(##{record.class.object_id})"             raise activerecord::associationtypemismatch, message           end         end  app/controllers/calendars_controller.rb:6:in `create' 

are missing something?

if use current_user.calendars.build(calendar_params), new calendar, no administration.

if use current_user.calendars.create(calendar_params), both administration , calendar saved database.

if want check whether calendar saved first, use approach:

def create   @calendar = calendar.build(calendar_params)   if @calendar.save     current_user.administrations << @calendar     flash[:success] = "calendar created!"     redirect_to root_url   else     render 'static_pages/home'   end end 

updated:

there error associate calendar user. should correct one:

def create   @calendar = current_user.calendars.build(calendar_params)   if @calendar.save     current_user.calendars << @calendar     flash[:success] = "calendar created!"     redirect_to root_url   else     render 'static_pages/home'   end end