rails系统关联工作半程

Question

我做了一个简单的联想--一个丰富的联合餐桌--通过参与向用户提供宴会，并通过参与为用户提供盛宴。但只有从侧面看，它才是完全合情合理的：

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

加载相关数据库：

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)

[1][1M][36 36mParticipation (1.0ms)←[0m←][1mSELECT participations.* FROM p articipations participations.id =？限制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>

问题是当我写到：

users.feasts 

正常工作

但相反的情况却不起作用：(尽管这完全是一种恭维！)

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>'

我的相关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

我甚至试图添加另一个索引

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

因此，这也将是系统的，但它不起作用。

该怎么办？？

Answer 1

您的feast变量实际上是ActiveRecord::Relation，而不是Feast的单个实例。您只能在Feast的实际实例上调用users。

如何加载feast变量？

Answer 2

我认为你的问题只是你没有正确地定义变量。

这会很好的

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

你有以下几点：

users.feasts 

rails抱怨您没有定义users。这是真的，你没有。

你是不是犯了一个错误？

feast = Feast.first
feast.users

这定义了一个局部变量users？因为它没有。

你可以

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

或

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

Answer 3

我在==>上面的问题中也写过

feast = feast.find(3)

当问题提出时，这并不是我真正写的。我真正做的是==>

feast = Feast.all 

因为我在数据库中只有一张盛宴记录，所以我不认为这是一个问题(所以我甚至没有在问题中提到它，并写了另一行作为示例)。

使宴会成为一个积极的关系对象。所以现在问题已经解决了，谢谢你的快速回答。