Rails 5：通过多态关系检索多个对象

Question

我需要通过多态关系检索多个对象，最好是单个查询。

在用户模式我有这样的：

class User < ApplicationRecord 
    has_many :companies, through: :accounts 
    has_many :permissions 
    has_many :medias, class_name: 'Media::Medias', through: :permissions, 
      source: :permitable, source_type: 'Media::Medias' 
end 

然后我权限模型看起来是这样的：

class Permission < ApplicationRecord 
    belongs_to :permitable, polymorphic: true 
    belongs_to :user, optional: true 
end 

媒体::媒体模式：

module Media 
    class Medias < ApplicationRecord 
    belongs_to :companies, optional: true, inverse_of: :medias 
    has_many :permissions, class_name: 'Permission', as: :permitable 
    has_many :users, through: :permissions 
    end 
end 

公司模式：

class Company < ApplicationRecord 
    has_many :accounts, dependent: :destroy 
    has_many :users, through: :accounts 
    has_many :medias, class_name: 'Media::Medias', inverse_of: :company 
end 

如何返回ActiveRecord::Relation object所有媒体的current_user和公司每个媒体？重要的是，我必须通过Permission模式使用关系，我不应该通过Accounts得到公司。到目前为止，我已经建立了模型，因此我可以使用Current.user.medias获取所有媒体的current_user。

谢谢！

更新

以下是我从几个版本的我试过了：

[4] pry(main)> user.medias.includes(:companies).map{|media| media.companies.id } 
    Media::Medias Load (1.4ms) SELECT "media_medias".* FROM "media_medias" INNER JOIN "permissions" ON "media_medias"."id" = "permissions"."permitable_id" WHERE "permissions"."user_id" = $1 AND "permissions"."permitable_type" = $2 [["user_id", 2], ["permitable_type", "Media::Medias"]] 
NameError: uninitialized constant Media::Medias::Companies 
from /home/ubuntu/.rvm/gems/ruby-2.3.3/gems/activerecord-5.1.0/lib/active_record/inheritance.rb:166:in `compute_type' 
[5] pry(main)> user.medias.preload(:companies).select(['medias.id', 'medias.company.id']) 
    Media::Medias Load (1.3ms) SELECT medias.id, medias.company.id FROM "media_medias" INNER JOIN "permissions" ON "media_medias"."id" = "permissions"."permitable_id" WHERE "permissions"."user_id" = $1 AND "permissions"."permitable_type" = $2 [["user_id", 2], ["permitable_type", "Media::Medias"]] 
=> #<Media::Medias::ActiveRecord_AssociationRelation:0x33dd094> 
[6] pry(main)> user.medias.select(['medias.id', 'medias.company_id']) 
    Media::Medias Load (1.1ms) SELECT medias.id, medias.company_id FROM "media_medias" INNER JOIN "permissions" ON "media_medias"."id" = "permissions"."permitable_id" WHERE "permissions"."user_id" = $1 AND "permissions"."permitable_type" = $2 [["user_id", 2], ["permitable_type", "Media::Medias"]] 
=> #<Media::Medias::ActiveRecord_AssociationRelation:0x3413234> 

更新2

[4] pry(main)> puts user.medias.preload(:companies).select(['medias.id', 'medias.company.id']) 
    Media::Medias Load (1.4ms) SELECT medias.id, medias.company.id FROM "media_medias" INNER JOIN "permissions" ON "media_medias"."id" = "permissions"."permitable_id" WHERE "permissions"."user_id" = $1 AND "permissions"."permitable_type" = $2 [["user_id", 2], ["permitable_type", "Media::Medias"]] 
ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR: missing FROM-clause entry for table "medias" 
LINE 1: SELECT medias.id, medias.company.id FROM "media_medias" INNE... 
      ^
: SELECT medias.id, medias.company.id FROM "media_medias" INNER JOIN "permissions" ON "media_medias"."id" = "permissions"."permitable_id" WHERE "permissions"."user_id" = $1 AND "permissions"."permitable_type" = $2 
from /home/ubuntu/.rvm/gems/ruby-2.3.3/gems/activerecord-5.1.0/lib/active_record/connection_adapters/postgresql_adapter.rb:620:in `async_exec' 
[5] pry(main)> puts user.medias.select(['medias.id', 'medias.company_id']) 
    Media::Medias Load (1.2ms) SELECT medias.id, medias.company_id FROM "media_medias" INNER JOIN "permissions" ON "media_medias"."id" = "permissions"."permitable_id" WHERE "permissions"."user_id" = $1 AND "permissions"."permitable_type" = $2 [["user_id", 2], ["permitable_type", "Media::Medias"]] 
ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR: missing FROM-clause entry for table "medias" 
LINE 1: SELECT medias.id, medias.company_id FROM "media_medias" INNE... 
      ^
: SELECT medias.id, medias.company_id FROM "media_medias" INNER JOIN "permissions" ON "media_medias"."id" = "permissions"."permitable_id" WHERE "permissions"."user_id" = $1 AND "permissions"."permitable_type" = $2 
from /home/ubuntu/.rvm/gems/ruby-2.3.3/gems/activerecord-5.1.0/lib/active_record/connection_adapters/postgresql_adapter.rb:620:in `async_exec' 

更新3

[1] pry(main)> User.find(2).medias.preload(:companies).select(['medias.id', 'medias.company.id']) 
    User Load (21.5ms) SELECT "users".* FROM "users" WHERE "users"."id" = $1 LIMIT $2 [["id", 2], ["LIMIT", 1]] 
    Media::Medias Load (1.7ms) SELECT medias.id, medias.company.id FROM "media_medias" INNER JOIN "permissions" ON "media_medias"."id" = "permissions"."permitable_id" WHERE "permissions"."user_id" = $1 AND "permissions"."permitable_type" = $2 [["user_id", 2], ["permitable_type", "Media::Medias"]] 
=> #<Media::Medias::ActiveRecord_AssociationRelation:0x17688f0> 
[2] pry(main)> User.find(2).medias.select(['medias.id', 'medias.company_id']) 
    User Load (1.7ms) SELECT "users".* FROM "users" WHERE "users"."id" = $1 LIMIT $2 [["id", 2], ["LIMIT", 1]] 
    Media::Medias Load (1.8ms) SELECT medias.id, medias.company_id FROM "media_medias" INNER JOIN "permissions" ON "media_medias"."id" = "permissions"."permitable_id" WHERE "permissions"."user_id" = $1 AND "permissions"."permitable_type" = $2 [["user_id", 2], ["permitable_type", "Media::Medias"]] 
=> #<Media::Medias::ActiveRecord_AssociationRelation:0x2155d90> 

Answer 1

为了解决这个问题，看起来像这个问题（或者至少是一个大问题）是模型名称和关联中复数/单数元素的混淆。一般情况下：

1. 型号名称是单数。在这种情况下，“中”是单数，“媒体”是复数。
2. 在模型中使用关联构造时，“has_many”通常会采用复数形式，而“belongs_to”将采用单数形式。所以，期待has_many :companies和belongs_to :user。
3. 基础表名是复数。所以，“中”模型是基于“媒体”表。

这样一来，我创建了一个简单的Rails应用程序，它是上述代码的最小工作示例。由于“帐户”模型没有出现，我从公司模型中删除了相应的元素。我还添加了反向关联。

class User < ApplicationRecord 
    has_many :permissions, inverse_of: :user 
    has_many :media, class_name: 'Medium::Medium', through: :permissions, source: :permitable, source_type: 'Medium::Medium' 
end 

class Company < ApplicationRecord 
    has_many :media, class_name: 'Medium::Medium', inverse_of: :company 
end 

class Medium::Medium < ApplicationRecord 
    belongs_to :company, optional: true, inverse_of: :media 
    has_many :permissions, class_name: 'Permission', as: :permitable, inverse_of: :permitable 
    has_many :users, through: :permissions 
end 

class Permission < ApplicationRecord 
    belongs_to :permitable, polymorphic: true, inverse_of: :permissions 
    belongs_to :user, inverse_of: :permissions 
end 

与测试数据样本控制台会话：

2.2.7 :001 > Company.create(name: 'IBM') 
    (0.1ms) begin transaction 
    SQL (0.4ms) INSERT INTO "companies" ("name", "created_at", "updated_at") VALUES (?, ?, ?) [["name", "IBM"], ["created_at", "2017-05-05 19:11:49.017155"], ["updated_at", "2017-05-05 19:11:49.017155"]] 
    (0.5ms) commit transaction 
=> #<Company id: 1, name: "IBM", created_at: "2017-05-05 19:11:49", updated_at: "2017-05-05 19:11:49"> 
2.2.7 :002 > User.create(name: 'Joe') 
    (0.0ms) begin transaction 
    SQL (0.8ms) INSERT INTO "users" ("name", "created_at", "updated_at") VALUES (?, ?, ?) [["name", "Joe"], ["created_at", "2017-05-05 19:11:59.401417"], ["updated_at", "2017-05-05 19:11:59.401417"]] 
    (2.3ms) commit transaction 
=> #<User id: 1, name: "Joe", created_at: "2017-05-05 19:11:59", updated_at: "2017-05-05 19:11:59"> 
2.2.7 :003 > Medium::Medium.create(name: 'TV') 
    (0.0ms) begin transaction 
    SQL (0.2ms) INSERT INTO "medium_media" ("name", "created_at", "updated_at") VALUES (?, ?, ?) [["name", "TV"], ["created_at", "2017-05-05 19:12:11.453440"], ["updated_at", "2017-05-05 19:12:11.453440"]] 
    (2.0ms) commit transaction 
=> #<Medium::Medium id: 1, company_id: nil, name: "TV", created_at: "2017-05-05 19:12:11", updated_at: "2017-05-05 19:12:11"> 
2.2.7 :004 > Medium::Medium.create(name: 'Newspaper') 
    (0.1ms) begin transaction 
    SQL (0.3ms) INSERT INTO "medium_media" ("name", "created_at", "updated_at") VALUES (?, ?, ?) [["name", "Newspaper"], ["created_at", "2017-05-05 19:12:18.433671"], ["updated_at", "2017-05-05 19:12:18.433671"]] 
    (2.0ms) commit transaction 
=> #<Medium::Medium id: 2, company_id: nil, name: "Newspaper", created_at: "2017-05-05 19:12:18", updated_at: "2017-05-05 19:12:18"> 
2.2.7 :005 > user = User.first 
    User Load (0.3ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT ? [["LIMIT", 1]] 
=> #<User id: 1, name: "Joe", created_at: "2017-05-05 19:11:59", updated_at: "2017-05-05 19:11:59"> 
2.2.7 :006 > user.permissions.create(permitable: Medium::Medium.first) 
    Medium::Medium Load (0.2ms) SELECT "medium_media".* FROM "medium_media" ORDER BY "medium_media"."id" ASC LIMIT ? [["LIMIT", 1]] 
    (0.0ms) begin transaction 
    SQL (0.2ms) INSERT INTO "permissions" ("permitable_type", "permitable_id", "user_id", "created_at", "updated_at") VALUES (?, ?, ?, ?, ?) [["permitable_type", "Medium::Medium"], ["permitable_id", 1], ["user_id", 1], ["created_at", "2017-05-05 19:12:50.694383"], ["updated_at", "2017-05-05 19:12:50.694383"]] 
    (0.5ms) commit transaction 
=> #<Permission id: 1, permitable_type: "Medium::Medium", permitable_id: 1, user_id: 1, created_at: "2017-05-05 19:12:50", updated_at: "2017-05-05 19:12:50"> 
2.2.7 :007 > user = User.first 
    User Load (0.2ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT ? [["LIMIT", 1]] 
=> #<User id: 1, name: "Joe", created_at: "2017-05-05 19:11:59", updated_at: "2017-05-05 19:11:59"> 
2.2.7 :008 > user.media 
    Medium::Medium Load (0.2ms) SELECT "medium_media".* FROM "medium_media" INNER JOIN "permissions" ON "medium_media"."id" = "permissions"."permitable_id" WHERE "permissions"."user_id" = ? AND "permissions"."permitable_type" = ? LIMIT ? [["user_id", 1], ["permitable_type", "Medium::Medium"], ["LIMIT", 11]] 
=> #<ActiveRecord::Associations::CollectionProxy [#<Medium::Medium id: 1, company_id: nil, name: "TV", created_at: "2017-05-05 19:12:11", updated_at: "2017-05-05 19:12:11">]> 
2.2.7 :009 > user.media.includes(:company) 
    Medium::Medium Load (0.2ms) SELECT "medium_media".* FROM "medium_media" INNER JOIN "permissions" ON "medium_media"."id" = "permissions"."permitable_id" WHERE "permissions"."user_id" = ? AND "permissions"."permitable_type" = ? LIMIT ? [["user_id", 1], ["permitable_type", "Medium::Medium"], ["LIMIT", 11]] 
=> #<ActiveRecord::AssociationRelation [#<Medium::Medium id: 1, company_id: nil, name: "TV", created_at: "2017-05-05 19:12:11", updated_at: "2017-05-05 19:12:11">]> 

只要确保让您的型号名称正确，它应该工作。示例代码可以在这里下载：

https://github.com/mdchaney/so_43765182

Answer 2

尝试在User类增加一个关联关系：

class User < ApplicationRecord 
    has_many :companies, through: :accounts 
    has_many :permissions 
    has_many :medias, class_name: 'Media::Medias', through: :permissions, 
     source: :permitable, source_type: 'Media::Medias' 
    has_many :media_companies, through: :medias, source: :companies 
end 

那么你应该能够做到： User.find(2).media_companies

既然你已经从媒体到公司belongs_to关联，那么你应该考虑使用在您的Media::Medias类中单数belongs_to :company。

如果你这样做，那么你将修改在User类的关联是：

has_many :media_companies, through: :medias, source: :company 

如果你想保持它的复数，那么你将需要添加一个关联选项得到它工作（避免NameError: uninitialized constant Media::Medias::Companies错误）：

module Media 
    class Medias < ApplicationRecord 
    belongs_to :companies, class_name: :Company, optional: true, inverse_of: :medias 
    ... 
    end 
end 

这将是更传统的，只是它切换到单数，但：

belongs_to :company, optional: true, inverse_of: :medias