Question

我正在开发的应用程序有3个主要模型和许多单表继承模型：

问题
用户
1. 专业
2. Representant
分类
1. 分类
2. 主题
3. 行业
4. 局部性
5. 区域
6. 国家

有多种用户（User，Professional < User，Representant < User），这些用户都继承自具有单表继承的User类。

有多种分类法（Category < Taxonomy，Topic < Taxonomy，Profession < Taxonomy，Locality < Taxonomy，Region < Taxonomy，Country < Taxonomy）都是从具有单表继承的Taxonomy类。

问题，以及专业人士也通过多对多的关系进行分类（他们可以有很多主题，许多专业，许多类别等......）

现在，我正在寻找一种方法来建立这些多态对象之间的多对多关系。我已经尝试了has_many :through解决方案并创建了一个Classification类。

迁移文件：

class CreateClassifications < ActiveRecord::Migration
  def change
    create_table :classifications, :id => false do |t|
      t.references :classifiable, :null => false, :default => 0, :polymorphic => true
      t.references :taxonomy,     :null => false, :default => 0, :polymorphic => true
    end

    add_index :classifications, [:classifiable_id, :taxonomy_id]
    add_index :classifications, [:taxonomy_id, :classifiable_id]
  end
end

模型文件：

class Classification < ActiveRecord::Base

  attr_accessible :classifiable, :classifiable_id, :classifiable_type,
                  :taxonomy, :taxonomy_id, :taxonomy_type

  belongs_to :classifiable, :polymorphic => true
  belongs_to :taxonomy,     :polymorphic => true

end

然后，我为问题，专业人士和分类法添加了has_many :through个关联。

Taxonomy.rb

has_many :classifications, :as => :taxonomy, :foreign_key => :taxonomy_id
has_many :classifiables, :through => :classifications, :source => :classifiable
has_many :users,         :through => :classifications, :source => :classifiable, :source_type => "User"
has_many :professionals, :through => :classifications, :source => :classifiable, :source_type => "Professional"
has_many :representants, :through => :classifications, :source => :classifiable, :source_type => "Representant"
has_many :questions,     :through => :classifications, :source => :classifiable, :source_type => "Question"
has_many :guides,        :through => :classifications, :source => :classifiable, :source_type => "Guide"

Question.rb

has_many :classifications, :as => :classifiable, :foreign_key => :classifiable_id, :dependent => :destroy
has_many :taxonomies, :through => :classifications, :source => :taxonomy
has_many :topics,     :through => :classifications, :source => :taxonomy, :source_type => "Topic"

Professional.rb

has_many :classifications, :as => :classifiable, :foreign_key => :classifiable_id, :dependent => :destroy
has_many :taxonomies,  :through => :classifications, :source => :taxonomy
has_many :topics,      :through => :classifications, :source => :taxonomy, :source_type => "Topic"
has_many :professions, :through => :classifications, :source => :taxonomy, :source_type => "Profession"

现在，在完成所有这些之后，事情不能很好地运作......

我似乎无法将分类标准分配给专业人员或问题（即Question.create(:title => "Lorem Ipsum Dolor Sit Amet", :author => current_user, :topics => [list of topics,...])除了未保存的主题外，效果很好。）
where子句无法正常工作（例如Question.joins(:topics).where(:conditions => {:topics => {:id => [list of topics,...]}})因no such column: "Topics"."id"错误而失败。

有任何帮助吗？谢谢！

更新

我已按照指示安装了gem'store_base_sti_class'。它对分类模型产生了预期的效果。

#<Classification classifiable_id: 1, classifiable_type: "Professional", taxonomy_id: 17, taxonomy_type: "Topic">

但是，当我查询主题（Professional.find(1).topics）时，ActiveRecord仍然在寻找“User”类而不是“Professional”...

SELECT "taxonomies".* FROM "taxonomies" INNER JOIN "classifications" ON "taxonomies"."id" = "classifications"."taxonomy_id" WHERE "taxonomies"."type" IN ('Topic') AND "classifications"."classifiable_id" = 1 AND "classifications"."classifiable_type" = 'User' AND "classifications"."taxonomy_type" = 'Topic'

知道如何解决这两个问题吗？

Answer 1

对于问题＃2，where子句中的键应映射到表名，而不是关联名。所以我想你会想要：

Question.joins(:topics).where(Topic.table_name => {:id => [...]})

对于问题＃1，当你设置question.topics = [...]时，似乎Rails创建的Classification对象被设置为taxonomy_type为“Taxonomy”（而不是“Topic”）。这似乎是由于Rails的through_association.rb：51，它将存储模型的base_class，而不仅仅是实际的类名。

我能够通过Classification模型上的before_validation回调解决这个问题。在我看来，替代方案是实际Rails关联代码的补丁，以使此行为可配置。

class Classification < ActiveRecord::Base
  attr_accessible :classifiable, :classifiable_id, :classifiable_type,
                  :taxonomy, :taxonomy_id, :taxonomy_type

  belongs_to :classifiable, polymorphic: true
  belongs_to :taxonomy, polymorphic: true
  before_validation :set_valid_types_on_polymorphic_associations

  protected

  def set_valid_types_on_polymorphic_associations
    self.classifiable_type = classifiable.class.model_name if classifiable
    self.taxonomy_type = taxonomy.class.model_name if taxonomy
  end
end

<强>更新

在设置关联范围时，似乎有另一个Rails决定（在preloader/association.rb:113中）使用model.base_class.sti_name而不是model.sti_name。

宝石应该为你照顾这个。请参阅store_base_sti_class_for_3_1_and_above.rb:135了解它如何包装has_many :as选项。在我的本地环境中，这可以按预期工作：

$ bundle exec rails console
irb(main):001:0> topics = 3.times.map { Topic.create }
irb(main):002:0> p = Professional.new
irb(main):003:0> p.topics = topics
irb(main):004:0> p.save!
irb(main):005:0> exit

$ bundle exec rails console
irb(main):001:0> puts Professional.find(1).topics.to_sql
SELECT "taxonomies".* FROM "taxonomies" INNER JOIN "classifications" ON "taxonomies"."id" = "classifications"."taxonomy_id" WHERE "taxonomies"."type" IN ('Topic') AND "classifications"."classifiable_id" = 2 AND "classifications"."classifiable_type" = 'Professional' AND "classifications"."taxonomy_type" IN ('Topic')
irb(main):002:0> Professional.find(1).topics.count
=> 3

Rails：类继承和复杂的多态has_many：通过关联

1 个答案: