Has_one 关联不起作用

Question

我不知道这个关系的错误在哪里：

class Education < ActiveRecord::Base
  attr_accessible :description, :graduation, :student_id, :faculty_id, :department_id

  has_one :faculty
  belongs_to :student
end
#  id          :integer          not null, primary key
#  student_id  :integer
#  faculty_id  :integer
#  description :text
#  graduation  :string(255)

class Faculty < ActiveRecord::Base
  attr_accessible :department_id, :name

  belongs_to :education
  belongs_to :department
end

# == Schema Information
#
# Table name: faculties
#
#  id            :integer          not null, primary key
#  name          :string(255)
#  department_id :integer

为什么我必须将education_id 添加到faculties 表中？ 每个教育只有一个教员，教员属于多个教育。

>> Education.last.faculty
  Education Load (0.3ms)  SELECT "educations".* FROM "educations" ORDER BY "educations"."id" DESC LIMIT 1
  Faculty Load (0.2ms)  SELECT "faculties".* FROM "faculties" WHERE "faculties"."education_id" = 1 LIMIT 1
SQLite3::SQLException: no such column: faculties.education_id: SELECT  "faculties".* FROM "faculties"  WHERE "faculties"."education_id" = 1 LIMIT 1
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: faculties.education_id: SELECT  "faculties".* FROM "faculties"  WHERE "faculties"."education_id" = 1 LIMIT 1
from /Users/rege/.rvm/gems/ruby-1.9.3-p194@ckdatabase/gems/sqlite3-1.3.6/lib/sqlite3/database.rb:91:in `initialize'

Answer 1

无论你在哪一边放置一个 'belongs_to' 都会有一个相关对象的 id - 它是根据定义来的。如果你属于某个东西，你就不属于另一个实例。

如果您希望每个教育只有一个教员，有两种选择：

• 使用一对一：当您还希望教师只有一种教育时
• 将 belongs_to 与一对多结合使用：当您希望每个教员拥有多个教育时

所以你可以试试这个：

class Education < ActiveRecord::Base
  attr_accessible :description, :graduation, :student_id, :faculty_id, :department_id

  belongs_to :faculty
  belongs_to :student
end

class Faculty < ActiveRecord::Base
  attr_accessible :department_id, :name

  has_many :education
  belongs_to :department
end

Answer 2

我认为你们的关系有些混乱 - official docs 可能会有所帮助。

如果我理解你想要做什么，你需要这样的东西（关于你的教师/教育关系）：

class Education < ActiveRecord::Base
  attr_accessible :description, :graduation, :student_id, :faculty_id, :department_id

  belongs_to :faculty # foreign key - faculty_id
  belongs_to :student
end
#  id          :integer          not null, primary key
#  student_id  :integer
#  faculty_id  :integer
#  description :text
#  graduation  :string(255)

class Faculty < ActiveRecord::Base
  attr_accessible :department_id, :name

  has_many :educations
  belongs_to :department
end