rails symetric association工作的一半

Question

i made a simple association - a rich joined table - feast to user through participation and user to feast through participation. but only on side works althogh it is totaly symeric:

user.rb:

class User < ActiveRecord::Base

  require 'digest/sha1'
  mount_uploader :image, ImageUploader

  has_many :participations
  has_many :feasts, :through => :participations

participation.rb:

class Participation < ActiveRecord::Base

  belongs_to :user
  belongs_to :feast

  has_many :obligations
  has_many :dishes, :through=> :obligations
  has_many :groceries, :as => :needed 

end

feast.rb:

class Feast < ActiveRecord::Base

  mount_uploader :image, ImageUploader

  has_many :participations
  has_many :users, :through => :participations

  has_many :courses
  has_many :dishes, :through=>:course

  has_many :groceries, :as => :needed  

  has_many :feast_invt, :as => :invitable

  validates_presence_of :feast_time
  validates_presence_of :feast_place


end

loading the relevant database:

irb(main):001:0> feast = Feast.find(1)

  ←[1m←[36mFeast Load (1.0ms)←[0m  ←[1mSELECT `feasts`.* FROM `feasts` WHERE `fe
asts`.`id` = ? LIMIT 1←[0m  [["id", 1]]

=> #<Feast id: 1, cost: nil, feast_place: "home", feast_time: "2014-03-14 00:00:
00", created_at: "2014-05-19 17:50:30", updated_at: "2014-05-19 17:50:30", image
: nil>

irb(main):002:0> user=User.find(3)

  ←[1m←[35mUser Load (1.0ms)←[0m  SELECT `users`.* FROM `users` WHERE `users`.`i
d` = ? LIMIT 1  [["id", 3]]

=> #<User id: 3, name: "elad bezalel", password: "", email: "
", hashed_password: "", creat
ed_at: "2014-05-14 18:30:46", updated_at: "2014-05-14 18:30:46", shop_cost: nil,
 salt: "", city: "", street_num
: "", entrance: "b", level: "3", apartment_num: "7", neighborhood: "
", kosher?: nil, image: "el4.jpg">
irb(main):003:0> par = Participation.find(1)

←[1m←[36mParticipation Load (1.0ms)←[0m ←[1mSELECT participations .* FROM p articipations WHERE participations . id = ? LIMIT 1←[0m [["id", 1]]

=> #<Participation id: 1, user_id: 3, feast_id: 1, created_at: "2014-05-19 17:54
:30", updated_at: "2014-05-19 17:54:30", user_costs: nil, meneger?: nil, accepte
d?: nil, coming???: nil>

irb(main):004:0>

the thing is that when i write:

users.feasts 

it works normally

but the opposite just doesn't work: (althogh it is totaly symetric!)

irb(main):002:0> feast.users


NoMethodError: undefined method `users' for #<ActiveRecord::Relation::ActiveReco
rd_Relation_Feast:0x548cfa0>


  from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activerecord-4
 .0.2/lib/active_record/relation/delegation.rb:121:in `method_missing'
    from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activerecord-4
 .0.2/lib/active_record/relation/delegation.rb:68:in `method_missing'
    from (irb):2
    from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.2
 /lib/rails/commands/console.rb:90:in `start'
    from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.2
 /lib/rails/commands/console.rb:9:in `start'
    from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.2
  /lib/rails/commands.rb:62:in `<top (required)>'
    from bin/rails:4:in `require'
    from bin/rails:4:in `<main>'

my relevant schema.rb:

create_table "feasts", force: true do |t|
    t.integer  "cost"
    t.string   "feast_place"
    t.datetime "feast_time"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.string   "image"
 end

create_table "participations", force: true do |t|
    t.integer  "user_id"
    t.integer  "feast_id"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.integer  "user_costs"
    t.boolean  "meneger?"
    t.boolean  "accepted?"
    t.string   "coming???"
  end

  add_index "participations", ["user_id", "feast_id"], name:          
             index_participations_on_user_id_and_feast_id", using: :btree

  create_table "users", force: true do |t|
     t.string   "name",            limit: 75
     t.string   "password",        limit: 40
     t.string   "email",                      default: "", null: false
     t.string   "hashed_password"
     t.datetime "created_at"
     t.datetime "updated_at"
     t.integer  "shop_cost"
     t.string   "salt"
     t.string   "city"
     t.string   "street_num"
     t.string   "entrance"
     t.string   "level"
     t.string   "apartment_num"
     t.string   "neighborhood"
     t.string   "kosher?"
     t.string   "image"
  end

end

i even tried to add another index

  "participations", ["feast_id", "user_id"]

so it will also be symetric but it did not work

what to do??

Answer 1

Your feast variable is actually an ActiveRecord::Relation, not a single instance of a Feast. You can only call users on an actual instance of a Feast.

How did you load the feast variable?

Answer 2

I think your problem is just that you're not defining variables properly.

This will work fine

user = User.find(1)
user.feasts
feast = Feast.find(1)
feast.users

You have the following:

users.feasts 

and rails complains that you haven't defined users . Which is true, you haven't.

Are you perhaps making the mistake of thinking that when you do

feast = Feast.first
feast.users

this has defined a local variable users ? Because it hasn't.

You could do

feast = Feast.first
users = feast.users
#=> a collection of users

or

feast = Feast.first
user = feast.users.first
user.feasts
#=> get a single user and call .feasts on it

Answer 3

althogh i wrote in my question above ==>

feast = feast.find(3)

that was not what i really wrote when the problem raised. what i really did is ==>

feast = Feast.all 

because i had only one feast record in the database, i did not think it is a problem(and so i did not even mention it in the question and wrote another line as an example).

that made feast to be an active relation object. so now the problem is fixed thanks for the quick answers.