RAILS 6 has_and_belongs_to_many >> join_table << 不起作用

Question

我想在两个多对多关系之间使用 join_table。

学生 -> join_table <- 老师

模型定义：

class Student < ApplicationRecord
    has_and_belongs_to_many :teachers, join_table: map_student_teacher
end

class Teacher < ApplicationRecord
    has_and_belongs_to_many :students, join_table: map_student_teacher
end

迁移定义：

class CreateStudents < ActiveRecord::Migration[6.0]
  def change
    create_table :students do |t|
      t.string : student_name
    end
  end
end

class CreateTeachers < ActiveRecord::Migration[6.0]
  def change
     create_table :teachers do |t|
       t.string : teacher_name
     end
  end
end


class CreateStudentsTeachersJoinTable < ActiveRecord::Migration[6.0]
  def change
     create_table :map_student_teacher, id: false do |t|
       t.belongs_to :student, index: true
       t.belongs_to :teacher, index: true
    end
  end
end

现在我有一个 seeds.rb 文件来初始化学生的名字。

students_defaults = ["hans","otto","paul","elsa"]

students_defaults.each do |name|
  Student.create(student_name: name) 
end

当我通过 rails db:seed 加载种子时我收到此错误消息：

rails aborted!
NameError: undefined local variable or method `map_student_teacher' for Student (call 'Student.connection' to establish a connection):Class
/home/sven/.rvm/gems/ruby-2.5.3/gems/activerecord-6.0.2.2/lib/active_record/dynamic_matchers.rb:22:in `method_missing'

出了什么问题？

Answer 1

在您的模型类中，它应该是 join_table: :map_student_teacher。注意额外的冒号使 map_student_teacher 成为一个符号。没有那个 Ruby 试图查看一个名为 map_student_teacher 的局部变量，它是未定义的。

class Student < ApplicationRecord
    has_and_belongs_to_many :teachers, join_table: :map_student_teacher
end

class Teacher < ApplicationRecord
    has_and_belongs_to_many :students, join_table: :map_student_teacher
end

如果这对你来说很难看，你也可以使用旧的 :join_table => :map_student_teacher 语法。

RAILS 6 has_and_belongs_to_many >> join_table << 不起作用

RAILS 6 has_and_belongs_to_many >> join_table << does not work

ruby-on-rails

ruby-on-rails-6