Rails ActiveRecord關係，STI和繼承

Question

好的，所以我寫了任何ruby代碼已經有好幾年了，而且我的設計可能不正確。考慮到這一點，我正在編寫一個小工具來通過REST克隆TargetProcess中的項目實體。目標進程的數據模型，允許多種類型的父：子關係：

project:epic:feature:user_story 
project:feature:user_story 
project:user_story 

然而，所有的實體是從數據結構的角度幾乎相同，因此它似乎是有道理的使用STI和使用模式定義關係和繼承。我創建了一個新的Rails應用程序只用這些模型來驗證我得到的錯誤，當我嘗試史詩與功能相關聯：

ActiveModel::MissingAttributeError: can't write unknown attribute `epic_id` 

下面是型號：

class TargetProcessEntity < ActiveRecord::Base 
end 

class Project < TargetProcessEntity 
    has_many :epics 
    has_many :features 
    has_many :user_stories 
end 

class Project < TargetProcessEntity 
    has_many :epics 
    has_many :features 
end 

class Epic < TargetProcessEntity 
    belongs_to :project 
    has_many :features 
end 

class Feature < TargetProcessEntity 
    belongs_to :project 
    belongs_to :epic 
    has_many :user_stories 
end 

class UserStory < TargetProcessEntity 
    belongs_to :feature 
    belongs_to :project 
end 

下面是模式：

ActiveRecord::Schema.define(version: 20150929122254) do 

    create_table "epics", force: :cascade do |t| 
    t.datetime "created_at",    null: false 
    t.datetime "updated_at",    null: false 
    t.integer "target_process_entity_id" 
    t.integer "project_id" 
    end 

    add_index "epics", ["project_id"], name: "index_epics_on_project_id" 
    add_index "epics", ["target_process_entity_id"], name: "index_epics_on_target_process_entity_id" 

    create_table "features", force: :cascade do |t| 
    t.integer "project_id" 
    t.integer "epic_id" 
    t.integer "target_process_entity_id" 
    end 

    add_index "features", ["epic_id"], name: "index_features_on_epic_id" 
    add_index "features", ["project_id"], name: "index_features_on_project_id" 
    add_index "features", ["target_process_entity_id"], name: "index_features_on_target_process_entity_id" 

    create_table "projects", force: :cascade do |t| 
    t.datetime "created_at",    null: false 
    t.datetime "updated_at",    null: false 
    t.integer "target_process_entity_id" 
    end 

    add_index "projects", ["id"], name: "index_projects_on_id" 
    add_index "projects", ["target_process_entity_id"], name: "index_projects_on_target_process_entity_id" 

    create_table "target_process_entities", force: :cascade do |t| 
    t.string "type",    null: false 
    t.string "name" 
    t.text  "description" 
    t.integer "source_remote_id" 
    t.float "numeric_priority" 
    t.integer "owner" 
    t.datetime "created_at",  null: false 
    t.datetime "updated_at",  null: false 
    t.integer "cloned_remote_id" 
    t.string "resource_type" 
    t.integer "project_id" 
    end 

    create_table "user_stories", force: :cascade do |t| 
    t.integer "project_id" 
    t.integer "feature_id" 
    t.datetime "created_at",    null: false 
    t.datetime "updated_at",    null: false 
    t.integer "target_process_entity_id" 
    end 

    add_index "user_stories", ["feature_id"], name: "index_user_stories_on_feature_id" 
    add_index "user_stories", ["project_id"], name: "index_user_stories_on_project_id" 
    add_index "user_stories", ["target_process_entity_id"], name: "index_user_stories_on_target_process_entity_id" 

end 

雖然史詩和特點都有一個PROJECT_ID，功能的實​​例不具有epic_id屬性;嘗試分配史詩爲特色炸燬：

[20] pry(main)> epic = Epic.new 
=> #<Epic:0x007fcab6c80590 
id: nil, 
type: "Epic", 
name: nil, 
description: nil, 
source_remote_id: nil, 
numeric_priority: nil, 
owner: nil, 
created_at: nil, 
updated_at: nil, 
cloned_remote_id: nil, 
resource_type: "Epic", 
project_id: nil> 
[21] pry(main)> feature = Feature.new 
=> #<Feature:0x007fcab6d3ba48 
id: nil, 
type: "Feature", 
name: nil, 
description: nil, 
source_remote_id: nil, 
numeric_priority: nil, 
owner: nil, 
created_at: nil, 
updated_at: nil, 
cloned_remote_id: nil, 
resource_type: "Feature", 
project_id: nil> 
[22] pry(main)> epic.save 
    (0.1ms) begin transaction 
    SQL (0.3ms) INSERT INTO "target_process_entities" ("type", "resource_type", "created_at", "updated_at") VALUES (?, ?, ?, ?) [["type", "Epic"], ["resource_type", "Epic"], ["created_at", "2015-10-02 15:18:13.351578"], ["updated_at", "2015-10-02 15:18:13.351578"]] 
    (4.6ms) commit transaction 
=> true 
[23] pry(main)> feature.epic = epic 
ActiveModel::MissingAttributeError: can't write unknown attribute `epic_id` 
from /Users/kcallahan/.rbenv/versions/2.0.0-p647/lib/ruby/gems/2.0.0/gems/activerecord-4.2.4/lib/active_record/attribute.rb:138:in `with_value_from_database' 
[24] pry(main)> 

我意識到這是極有可能，我要麼做錯事或已經做出了糟糕的設計決定;任何輸入都非常感謝，因爲我一直無法找到任何東西，並且幾天來一直在抨擊我的頭！

Answer 1

好吧，我幾乎是錯誤地工作了！我將xxx_id列添加到了target_process_entities表。我認爲STI表格能夠對關係定義做出反應，儘管我對STI和關係的內部工作原理的理解充其量是生鏽的和不完整的...

Answer 2

我可能是錯的，但它看起來像您的功能表是Project和Epic之間多對多關係的連接表。

如果是這樣的話，你的模型可能看起來像這樣

class Project < TargetProcessEntity 
    has_many :features 
    has_many :epics, through: :features 
end 

class Epic < TargetProcessEntity 
    has_many :features 
    has_many :projects, through: :features 
end 

class Feature < TargetProcessEntity 
    belongs_to :project 
    belongs_to :epic 
    has_many :user_stories 
end 

如果使用相同的名稱

http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html