Question

我在SO question中提出了完全相同的问题。

我的答案实现如下：

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  ##### The next two lines are the important part ######
  has_many   :notes, class_name: LessonNotes::Engine::Note, foreign_key: "teacher_id"
  has_many   :notes, class_name: LessonNotes::Engine::Note, foreign_key: "student_id"

  has_many   :students, class_name:  "User",
                        foreign_key: "teacher_id"
  belongs_to :teacher,  class_name:  "User"
end

但是，我收到此错误：uninitialized constant LessonNotes::Engine::Note

如果我删除引擎上的has_many个关联之一并离开另一个，那么一切正常......但

更新

通过更改相关的两行来消除uninitialized constant错误：

has_many   :notes, class_name: "::LessonNotes::Engine::Note", foreign_key: "student_id"
has_many   :notes, class_name: "::LessonNotes::Engine::Note", foreign_key: "teacher_id"

但是现在似乎第二个协会会覆盖第一个协会。 ActiveRecord只查找第二个外键 - 在本例中为“teacher_id” - 并忽略第一个外键。这是预期的行为吗？

Answer 1

是的，这是预期的行为。您正在定义相同的关联（按名称：注释）两次，因此第二个声明将覆盖第一个。

您必须重命名关联。

has_many   :student_notes, class_name: "::LessonNotes::Engine::Note", foreign_key: "student_id"
has_many   :teacher_notes, class_name: "::LessonNotes::Engine::Note", foreign_key: "teacher_id"

如果你想同时访问这两个，你可以定义类似这样的东西

def notes
  student_notes + teacher_notes
end

与引用引擎的多个外键关联

1 个答案: