ruby-on-rails - Rails STI 和 has_many 通过关联不起作用，SQLException : no such table

Question

我有以下模型:

class Test < ApplicationRecord
end

class Exam < Test
end

class Practice < Test
  has_many :relations
  has_many :questions, through: :relations
end

class Relation < ApplicationRecord
  belongs_to :practice
  belongs_to :question
end

class Question < ApplicationRecord
  has_many :relations
  has_many :practices, through: :relations
end

这是我的模式:

 create_table "questions", force: :cascade do |t|
    t.string "title"
    t.text "text"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

  create_table "relations", force: :cascade do |t|
    t.integer "practice_id"
    t.integer "question_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["practice_id"], name: "index_relations_on_practice_id"
    t.index ["question_id"], name: "index_relations_on_question_id"
  end

  create_table "tests", force: :cascade do |t|
    t.string "name"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

当我在 Rails 控制台中尝试时:

@p = Practice.new
@p.save
@q = Question.new 
@q.save

Practice.last.questions << Question.last

我收到这个错误:

Question Load (0.2ms)  SELECT  "questions".* FROM "questions" ORDER BY "questions"."id" DESC LIMIT ?  [["LIMIT", 1]]
   (0.1ms)  begin transaction
  SQL (0.4ms)  INSERT INTO "relations" ("practice_id", "question_id", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["practice_id", 2], ["question_id", 1], ["created_at", "2017-10-26 06:09:42.581082"], ["updated_at", "2017-10-26 06:09:42.581082"]]
   (0.1ms)  rollback transaction
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such table: main.practices: INSERT INTO "relations" ("practice_id", "question_id", "created_at", "updated_at") VALUES (?, ?, ?, ?)

错误很明显，它没有找到表格 practices 但我该如何解决这个问题？我不明白如何指定使用表测试，而不是实践。感谢任何帮助

Answer 1

不应该有 practices 表，因为 Practice 继承 Test 并且您想使用 STI 模式。我已经在我的机器上重复了您的模型和模式，它按预期工作。所以要么你在使用 SQLite 或使用 spring 之类的东西时遇到了一些问题。

使用 spring stop 使 spring 平静下来，然后尝试使用 rails db:reset 重新创建数据库并确保没有错误。

此外，我希望这只是示例代码，在现实生活中你不会将 sql 关系命名为 relations =)